[go: up one dir, main page]
More Web Proxy on the site http://driver.im/
Next Issue
Volume 2, September
Previous Issue
Volume 2, March
You seem to have javascript disabled. Please note that many of the page functionalities won't work as expected without javascript enabled.
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
3.9
2.6
Journals
Magnetochemistry
Volume 2
Issue 2
share announcement

Magnetochemistry, Volume 2, Issue 2 (June 2016) – 9 articles

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Reader to open them.
Order results
Result details
Section
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
1369 KiB  
Article
Multiple Magnetization Reversal Channels Observed in a 3d-4f Single Molecule Magnet
by Asma Amjad, Albert Figuerola, Andrea Caneschi and Lorenzo Sorace
Magnetochemistry 2016, 2(2), 27; https://doi.org/10.3390/magnetochemistry2020027 - 14 Jun 2016
Cited by 14 | Viewed by 5069
Abstract
The present study discusses the magnetic dynamics of a previously reported cyanide bridged 3d-4f dinuclear DyIIICoIII complex. Following the axial anisotropy suggested by previous Electron Paramagnetic Resonance spectroscopy (EPR) analysis, the complex turned out to show slow relaxation of the [...] Read more.
The present study discusses the magnetic dynamics of a previously reported cyanide bridged 3d-4f dinuclear DyIIICoIII complex. Following the axial anisotropy suggested by previous Electron Paramagnetic Resonance spectroscopy (EPR) analysis, the complex turned out to show slow relaxation of the magnetization at cryogenic temperature, and this was studied in different temperature and field regimes. The existence of multichannel relaxation pathways that reverse the magnetization was clearly disclosed: a tentative analysis suggested that these channels can be triggered and controlled as a function of applied static magnetic field and temperature. Persistent evidence of a temperature independent process even at higher fields, attributable to quantum tunneling, is discussed, while the temperature dependent dynamics is apparently governed by an Orbach process. The broad distribution of relaxation rates evidenced by the ac susceptibility measurements suggest a relevant role of the intermolecular interactions in this system. Full article
(This article belongs to the Special Issue Magnetic Anisotropy)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>View of the core of <b>DyCo</b> [<a href="#B17-magnetochemistry-02-00027" class="html-bibr">17</a>]. Color code: <b>blue</b>: Co<sup>III</sup>; <b>grey</b>: C; <b>cyan</b>: N; <b>red</b>: O; <b>green</b>: Dy<sup>III</sup>.</p> Full article ">Figure 2
<p>(<b>a</b>) Frequency dependence of the out-of-phase χ′′ component of the molar AC susceptibility of <b>DyCo</b> measured at 2 K at variable external static magnetic field (<b>red</b> 0 Oe to <b>blue</b> 5 KOe). The solid lines are Debye fits at respective fields; (<b>b</b>) Field dependent behavior of the relaxation time observed at 2 K; the solid line is a semi-quantitative fit to the data obtained with parameters reported in the text.</p> Full article ">Figure 3
<p>Arrhenius plot of the temperature dependence of the magnetic relaxation time <span class="html-italic">τ</span> of <b>DyCo</b>, in the presence of a dc magnetic field 300 Oe. The solid line is a fit corresponding to Equation (3) with the best fit parameters reported in the text.</p> Full article ">Figure 4
<p>(<b>a</b>) Observation of two identifiable temperature dependent relaxation phenomena in <b>DyCo</b>, in the presence of a static magnetic field of 2 KOe; (<b>b</b>) Temperature behavior of the relaxation rates extracted for the two relaxation phenomena from the Debye fit of the ac data at 2 KOe. The solid lines are the best fit to Equation (3) with the parameters explained in the text. Black squares are the relaxation rate observed at 300 Oe, reported here for comparison’s sake.</p> Full article ">Figure 5
<p>(<b>a</b>) Frequency dependence of the out-of-phase χ′′ component of the susceptibility measured at 4 K at variable external static magnetic field. The solid lines are guide for eyes; (<b>b</b>) Field dependent behavior of the relaxation time observed at 4 K, extracted from the Debye fit of the AC data, the solid lines represent the best attainable fit.</p> Full article ">
3792 KiB  
Communication
Slow Magnetic Relaxation in Unprecedented Mono-Dimensional Coordination Polymer of Ytterbium Involving Tetrathiafulvalene-Dicarboxylate Linker
by Anjara Belio Castro, Julie Jung, Stéphane Golhen, Boris Le Guennic, Lahcène Ouahab, Olivier Cador and Fabrice Pointillart
Magnetochemistry 2016, 2(2), 26; https://doi.org/10.3390/magnetochemistry2020026 - 11 May 2016
Cited by 17 | Viewed by 5369
Abstract
A one-dimensional compound has been constructed through a YbIII ion and bridging redox-active deprotonated 4,5-bis(carboxylic)-4′,5′-methyldithiotetrathiafulvene. This polymer displays slow magnetic relaxation due to the planar magnetic anisotropy of the YbIII, which has been experimentally determined. Full article
(This article belongs to the Special Issue Magnetic Anisotropy)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Ortep view of the asymmetric unit of <b>Yb</b>. Thermal ellipsoids are drawn at 30% probability. Hydrogen atoms and water molecules of crystallization are omitted for clarity; and (<b>b</b>) representation of the one-dimensional structure running along the <span class="html-italic">b</span> axis.</p> Full article ">Figure 2
<p>Packing along the <span class="html-italic">a</span> direction of the TTF moieties. The van der Waals surface of the TTF cores of the coordinated and non-coordinated TTFs are represented while coordination polyhedra of Yb<sup>III</sup> are also shown (in green).</p> Full article ">Figure 3
<p>Angular dependence of χ<sub>M</sub>T of a single crystal rotated in three perpendicular planes with <span class="html-italic">H</span> = 10 kOe at 2 K. Best fitted curves are in full lines.</p> Full article ">Figure 4
<p>Principal magnetic axes (<span class="html-italic">g</span><sub>x</sub>: blue, <span class="html-italic">g</span><sub>y</sub>: green, <span class="html-italic">g</span><sub>z</sub>: red) of <b>Yb</b>.</p> Full article ">Figure 5
<p>Frequency dependences of the in-phase (χ<sub>M</sub>′) and out-of-phase (χ<sub>M</sub>ʺ) components of the ac susceptibility measured between 1.8 and 6 K in an external DC field of 1 kOe. Insert: temperature dependence of the relaxation time with the best-fitted curve (see text).</p> Full article ">
1338 KiB  
Article
Torque-Detected Electron Spin Resonance as a Tool to Investigate Magnetic Anisotropy in Molecular Nanomagnets
by María Dörfel, Michal Kern, Heiko Bamberger, Petr Neugebauer, Katharina Bader, Raphael Marx, Andrea Cornia, Tamoghna Mitra, Achim Müller, Martin Dressel, Lapo Bogani and Joris Van Slageren
Magnetochemistry 2016, 2(2), 25; https://doi.org/10.3390/magnetochemistry2020025 - 6 May 2016
Cited by 5 | Viewed by 5775
Abstract
The method of choice for in-depth investigation of the magnetic anisotropy in molecular nanomagnets is high-frequency electron spin resonance (HFESR) spectroscopy. It has the benefits of high resolution and facile access to large energy splittings. However, the sensitivity is limited to about 10 [...] Read more.
The method of choice for in-depth investigation of the magnetic anisotropy in molecular nanomagnets is high-frequency electron spin resonance (HFESR) spectroscopy. It has the benefits of high resolution and facile access to large energy splittings. However, the sensitivity is limited to about 107 spins for a reasonable data acquisition time. In contrast, methods based on the measurement of the deflection of a cantilever were shown to enable single spin magnetic resonance sensitivity. In the area of molecular nanomagnets, the technique of torque detected electron spin resonance (TDESR) has been used sporadically. Here, we explore the applicability of that technique by investigating molecular nanomagnets with different types of magnetic anisotropy. We also assess different methods for the detection of the magnetic torque. We find that all types of samples are amenable to these studies, but that sensitivities do not yet rival those of HFESR. Full article
(This article belongs to the Special Issue Magnetic Anisotropy)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) schematic drawing of the bottom part of the sample rod, showing the sliding sample holder. This allows switching between an aperture for alignment purposes, and the cantilever (dark brown, with yellow bottom plate); (<b>b</b>) setup for optical detection of the cantilever deflection by means of a laser and position-sensitive detector (PSD); (<b>c</b>) field-domain torque-detected electron spin resonance (TDESR) measurements on a single crystal of Fe<sub>4</sub> with the crystal <span class="html-italic">c</span>-axis at 32° from the easy axis and different temperatures as indicated, with raw curves on top and the baseline-corrected spectra on the bottom.</p> Full article ">Figure 2
<p>(<b>a</b>) capacitively detected frequency-domain TDESR spectra recorded on a single crystal of Mn<sub>12</sub>Ac with the applied field 4° from the easy axis (<span class="html-italic">c</span>), at 7 K and different fields as indicated; (<b>b</b>) optically detected frequency-domain TDESR spectra recorded on a single crystal of Mn<sub>12</sub>Ac with the crystal <span class="html-italic">c</span>-axis 45° from the field, at 7 K and different fields as indicated. In both panels, solid lines are experimental data and dashed lines represent the simulations.</p> Full article ">Figure 3
<p>(<b>a</b>) capacitance as a function of angle for a single crystal of V<sub>15</sub> at 7 K and different fields as indicated. Symbols represent experimental data while solid lines are calculated data; (<b>b</b>) frequency-domain CD-TDESR spectra recorded on a single crystal of V<sub>15</sub> with the field 2° from the unique crystal [1 1 1]-axis, at 2 K and different fields as indicated. The solid and dashed lines are the measured and simulated spectra, respectively.</p> Full article ">Figure 4
<p>(<b>a</b>) capacitance as a function of angle for a single crystal of Cu-mnt at 7 K and different fields as indicated. The upper panel displays the individual contributions of the two molecules in the monoclinic unit cell; (<b>b</b>) capacitively detected frequency-domain TDESR spectra recorded on a single crystal of Cu-mnt at 2 K at different fields as indicated. Spectra are reported for different angles arising from different angles θ = 20° (light grey, light green, orange), 30° (grey, green, red), and 40° (dark grey, olive, dark red). The upper graph shows the simulated electron spin resonance (ESR) absorption spectra with parameters given in the text.</p> Full article ">
1605 KiB  
Article
Surface Effects Leading to Unusual Size Dependence of the Thermal Hysteresis Behavior in Spin-Crossover Nanoparticles
by Jorge Linares, Catalin Maricel Jureschi and Kamel Boukheddaden
Magnetochemistry 2016, 2(2), 24; https://doi.org/10.3390/magnetochemistry2020024 - 3 May 2016
Cited by 30 | Viewed by 5912
Abstract
We analyze the size effect on spin-crossover transition nanoparticles in a 2D Ising-like model subject to a specific ligand-field at the surface. By anisotropic sampling method applied to the finite 2D square Ising lattices with various sizes, we determined the density of macro [...] Read more.
We analyze the size effect on spin-crossover transition nanoparticles in a 2D Ising-like model subject to a specific ligand-field at the surface. By anisotropic sampling method applied to the finite 2D square Ising lattices with various sizes, we determined the density of macro states by scanning the spin configurations. This information, which is independent on the system parameters, is used to exactly calculate the thermal behavior of spin-crossover nanoparticles whose ligand-field of the atoms at the surface is lower than those of the bulk. We found that decreasing the size of the nanoparticles leads to a global increase of the effective interaction, which has the consequence to enhance the width of the thermal hysteresis. This unusual behavior opens a new avenue in controlling the bistability characteristics at small scale, one of the important conditions of applicability of these materials at the nanometric scale. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) The simulated thermal behavior of the total high-spin (HS) fraction, <span class="html-italic">n<sub>HS</sub></span>(<span class="html-italic">T</span>), for different system sizes, showing an increase of the thermal hysteresis width for smaller nanoparticle sizes; (<b>b</b>) Enlarged view of the simulated thermal behavior of the total HS fraction, <span class="html-italic">n<sub>HS</sub></span>(<span class="html-italic">T</span>), for <span class="html-italic">N<sub>t</sub></span> = 16(4 × 4) molecules, showing the stable (red square), metastable: <span class="html-italic">m</span> (black and green stars) and unstable (blue dots) regions: only the stable and metastable states are observed at thermal equilibrium. The computational parameters are: Δ/<span class="html-italic">k<sub>B</sub></span> = 1300 K, <span class="html-italic">G</span>/<span class="html-italic">k<sub>B</sub></span> = 172.7 K, <span class="html-italic">J</span>/<span class="html-italic">k<sub>B</sub></span> = 15 K, <span class="html-italic">L</span>/<span class="html-italic">k<sub>B</sub></span> = 120 K, ln(<span class="html-italic">g</span>) = 6.01.</p> Full article ">Figure 2
<p>The thermal behavior for the edge, inner and total molecules of the system for the cases: (<b>a</b>) <span class="html-italic">N<sub>t</sub></span> = 16 (4 × 4) and (<b>b</b>) <span class="html-italic">N<sub>t</sub></span> = 144 (12 × 12). The model parameters are the same as those of <a href="#magnetochemistry-02-00024-f001" class="html-fig">Figure 1</a>.</p> Full article ">Figure 3
<p>The size-dependence of <math display="inline"> <semantics> <mrow> <msubsup> <mi>N</mi> <mi>x</mi> <mn>2</mn> </msubsup> <msub> <mi>T</mi> <mrow> <mi>e</mi> <mi>q</mi> </mrow> </msub> </mrow> </semantics> </math> showing a parabolic behavior for the bulk contribution and a quasi-linear trend for that of the surface, in qualitative good agreement with analytical predictions of Equation (20).</p> Full article ">Figure 4
<p>Size dependence of the global transition temperature showing an excellent agreement between MC (Monte Carlo) simulations (blue circles) and analytical predictions (red squares) of Equation (19). The computational parameters were: Δ/<span class="html-italic">k<sub>B</sub></span> = 1300 K, <span class="html-italic">G</span>/<span class="html-italic">k<sub>B</sub></span> = 172.7 K, <span class="html-italic">J</span>/<span class="html-italic">k<sub>B</sub></span> = 15 K, <span class="html-italic">L</span>/<span class="html-italic">k<sub>B</sub></span> = 120 K, ln(<span class="html-italic">g</span>) = 6.01.</p> Full article ">Figure 5
<p>(<b>a</b>) The order-disorder temperature, <span class="html-italic">T<sub>O.D.</sub></span>, calculated for different system sizes; (<b>b</b>) zoom around the critical temperatures, showing the increase of <span class="html-italic">T<sub>O.D.</sub></span> with size; and (<b>c</b>) <span class="html-italic">T<sub>OD</sub> versus</span> <math display="inline"> <semantics> <mrow> <msqrt> <mrow> <msub> <mi>N</mi> <mi>x</mi> </msub> <mo>−</mo> <mn>4</mn> </mrow> </msqrt> </mrow> </semantics> </math> showing a linear behavior. The red dashed line is the best linear fit. The computational parameters are: <span class="html-italic">Δ</span>/<span class="html-italic">k<sub>B</sub></span> = 0 K, <span class="html-italic">G</span>/<span class="html-italic">k<sub>B</sub></span> = 172.7 K, <span class="html-italic">J</span>/<span class="html-italic">k<sub>B</sub></span> = 15 K, <span class="html-italic">L</span>/<span class="html-italic">k<sub>B</sub></span> = 0 K, ln(<span class="html-italic">g</span>) = 0.</p> Full article ">Figure 6
<p>Size dependence of the thermal hysteresis width showing a drop of the bistability for nanoparticle larger than 6 × 6. The model parameters are the same as those of <a href="#magnetochemistry-02-00024-f001" class="html-fig">Figure 1</a>.</p> Full article ">
7199 KiB  
Article
Evidence of Slow Magnetic Relaxation in Co(AcO)2(py)2(H2O)2
by James P. S. Walsh, Graeme Bowling, Ana-Maria Ariciu, Nur F. M. Jailani, Nicholas F. Chilton, Paul G. Waddell, David Collison, Floriana Tuna and Lee J. Higham
Magnetochemistry 2016, 2(2), 23; https://doi.org/10.3390/magnetochemistry2020023 - 20 Apr 2016
Cited by 35 | Viewed by 7150
Abstract
The monometallic pseudo-octahedral complex, [Co(H2O)2(CH3COO)2(C5H5N)2], is shown to exhibit slow magnetic relaxation under an applied field of 1500 Oe. The compound is examined by a combination of experimental and [...] Read more.
The monometallic pseudo-octahedral complex, [Co(H2O)2(CH3COO)2(C5H5N)2], is shown to exhibit slow magnetic relaxation under an applied field of 1500 Oe. The compound is examined by a combination of experimental and computational techniques in order to elucidate the nature of its electronic structure and slow magnetic relaxation. We demonstrate that any sensible model of the electronic structure must include a proper treatment of the first-order orbital angular momentum, and we find that the slow magnetic relaxation can be well described by a two-phonon Raman process dominating at high temperature, with a temperature independent quantum tunnelling pathway being most efficient at low temperature. Full article
(This article belongs to the Special Issue Magnetic Anisotropy)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Crystal structure of compound <b>1</b> and a packing diagram viewing almost along the <span class="html-italic">b</span>-axis.</p> Full article ">Figure 2
<p>Plots of <span class="html-italic">χ<sub>M</sub>T</span>(<span class="html-italic">T</span>) measured under a static field of 0.1 T (main) and field-dependent magnetisation at 2 and 4 K (inset) for compound <b>1</b>. Red traces are simulations using the T, P isomorphism model described in the main text.</p> Full article ">Figure 3
<p>Orientation of the principal axes for the <math display="inline"> <semantics> <mrow> <mover accent="true"> <mi>S</mi> <mo>˜</mo> </mover> <mo>=</mo> <mn>1</mn> <mo>/</mo> <mn>2</mn> </mrow> </semantics> </math> effective <span class="html-italic">g</span>-values of the ground Kramers doublet for <b>1</b>. Red = hard axis, <span class="html-italic">g<sub>x</sub></span>; green = intermediate axis, <span class="html-italic">g<sub>y</sub></span>; blue = easy axis, <span class="html-italic">g<sub>z</sub></span>.</p> Full article ">Figure 4
<p>(<b>a</b>) Frequency dependence of the imaginary ac susceptibility of <b>1</b> measured at 1.8 K and under several applied fields. The lines are guides for the eye; (<b>b</b>) Field dependence of the relaxation time at 1.8 K.</p> Full article ">Figure 5
<p>Frequency dependence of the (<b>a</b>) real and (<b>b</b>) imaginary ac susceptibilities of <b>1</b> measured under a static field of 1500 Oe and temperatures 1.8–10 K. Solid lines are guides for the eye.</p> Full article ">Figure 6
<p>Temperature dependence of (<b>a</b>) <span class="html-italic">χ′<sub>M</sub>T</span> and (<b>b</b>) <span class="html-italic">χ</span>″<sub>M</sub> for <b>1</b> measured under a static field of 1500 Oe and an ac field of 1.55 Oe oscillating at frequencies from 1 to 1400 Hz.</p> Full article ">Figure 7
<p>Cole-Cole plot of the measured ac susceptibility data for <b>1</b> showing fits obtained using the generalised Debye model (red traces). Inset graph shows the plot of ln(τ) against 1/<span class="html-italic">T</span>, and a fit to Equation (4) with the parameters given in the text (red line).</p> Full article ">
4636 KiB  
Review
Ferromagnetic Multilayers: Magnetoresistance, Magnetic Anisotropy, and Beyond
by Conrad Rizal, Belaid Moa and Boris B. Niraula
Magnetochemistry 2016, 2(2), 22; https://doi.org/10.3390/magnetochemistry2020022 - 16 Apr 2016
Cited by 34 | Viewed by 13228
Abstract
Obtaining highly sensitive ferromagnetic, FM, and nonmagnetic, NM, multilayers with a large room-temperature magnetoresistance, MR, and strong magnetic anisotropy, MA, under a small externally applied magnetic field, H, remains a subject of scientific and technical interest. Recent advances in nanofabrication and characterization techniques [...] Read more.
Obtaining highly sensitive ferromagnetic, FM, and nonmagnetic, NM, multilayers with a large room-temperature magnetoresistance, MR, and strong magnetic anisotropy, MA, under a small externally applied magnetic field, H, remains a subject of scientific and technical interest. Recent advances in nanofabrication and characterization techniques have further opened up several new ways through which MR, sensitivity to H, and MA of the FM/NM multilayers could be dramatically improved in miniature devices such as smart spin-valves based biosensors, non-volatile magnetic random access memory, and spin transfer torque nano-oscillators. This review presents in detail the fabrication and characterization of a few representative FM/NM multilayered films—including the nature and origin of MR, mechanism associated with spin-dependent conductivity and artificial generation of MA. In particular, a special attention is given to the Pulsed-current deposition technique and on the potential industrial applications and future prospects. FM multilayers presented in this review are already used in real-life applications such as magnetic sensors in automobile and computer industries. These material are extremely important as they have the capability to efficiently replace presently used magnetic sensors in automobile, electronics, biophysics, and medicine, among many others. Full article
(This article belongs to the Special Issue Magnetic Anisotropy)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a-i</b>) Crystallographic orientation of hcp-Co and (<b>a-ii</b>) corresponding magnetization curves. The magnetization prefers to align with a specific crystallographic direction (e.g., the hexagonal axis in Co). The anisotropy constant for pure Co, <math display="inline"> <semantics> <msub> <mi>K</mi> <mrow> <mi>u</mi> <mn>1</mn> </mrow> </msub> </semantics> </math> = 5 × 10<math display="inline"> <semantics> <msup> <mrow/> <mn>6</mn> </msup> </semantics> </math> erg/cc (20 <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math> eV/atom) [<a href="#B39-magnetochemistry-02-00022" class="html-bibr">39</a>]. (<b>b</b>) structure showing magnetic alignment from antiparallel to parallel due to H field; (<b>c</b>) Schematic of inducing strain, <span class="html-italic">ϵ</span> in the sample: In (<b>c-i</b>), position of the multilayer films, the direction of the applied mechanical force, and the position of the electromagnets; and (<b>c-ii</b>), directions of the applied mechanical and magnetic forces, and the direction of correspondingly the induced magnetic easy axis, Adapted from [<a href="#B40-magnetochemistry-02-00022" class="html-bibr">40</a>], Copyright AIP Publishing LLC, 2012; (<b>d</b>) The peak of the GMR corresponding to <math display="inline"> <semantics> <msub> <mi>H</mi> <mi>c</mi> </msub> </semantics> </math>; (<b>e</b>) FM Multilayers for <math display="inline"> <semantics> <mi mathvariant="sans-serif">ϵ</mi> </semantics> </math> = 0 and <math display="inline"> <semantics> <mi mathvariant="sans-serif">ϵ</mi> </semantics> </math> ≠ 0 case; (<b>f</b>) A relationship between the magnetic anisotropy constant, <math display="inline"> <semantics> <msub> <mi>K</mi> <mi>u</mi> </msub> </semantics> </math>, and the induced <math display="inline"> <semantics> <mi mathvariant="sans-serif">ϵ</mi> </semantics> </math>. The inset shows M-H curves when the <math display="inline"> <semantics> <mi mathvariant="sans-serif">ϵ</mi> </semantics> </math> is changed in the range of 1.5%. Adapted from [<a href="#B40-magnetochemistry-02-00022" class="html-bibr">40</a>], Copyright AIP Publishing LLC, 2012.</p> Full article ">Figure 2
<p>Schematic showing various functional effects in ferromagnetic (FM), multilayered films (<b>a</b>) Giant magnetoresistance (GMR), effect in Fe/Cr multilayers. Adapted from [<a href="#B1-magnetochemistry-02-00022" class="html-bibr">1</a>]. (<b>b-i</b>) GMR effect in Fe/Cr multilayers; (<b>b-ii</b>) GMR effect, function as a Cr layer thickness, <math display="inline"> <semantics> <msub> <mi>t</mi> <mrow> <mi>C</mi> <mi>r</mi> </mrow> </msub> </semantics> </math>, measured at room temperature and at 4 K. The GMR effect is periodic in nature and it varies with <math display="inline"> <semantics> <msub> <mi>t</mi> <mrow> <mi>C</mi> <mi>r</mi> </mrow> </msub> </semantics> </math>; (<b>b-iii</b>) shows the MR measurement arrangement; (<b>c-i, ii</b>) observed magnetic anisotropy. Reproduced with permission from [<a href="#B3-magnetochemistry-02-00022" class="html-bibr">3</a>], Copyright AIP Publishing LLC, 1993. And (<b>d</b>) new devices using spin functionalities.</p> Full article ">Figure 3
<p>(<b>a</b>) A Schematic of a Co/Cu multilayer; (<b>b</b>), Magnetoresistance (MR), for the Co/Cu multilayers at room temperature and 4 K (the subscript 30 in the inset indicates the number of bilayers). The MR is oscillatory in nature and it varies with the Cu layer thickness. The peak of the MR curves corresponds to the antiferromagnetic alignment of magnetic moments in the adjacent Co layers as denoted by AFM in the diagram. Reproduced with permission from [<a href="#B46-magnetochemistry-02-00022" class="html-bibr">46</a>], Copyright Elsevier, 1994.</p> Full article ">Figure 4
<p>Commonly used fabrication processes: physical vapor deposition and chemical deposition.</p> Full article ">Figure 5
<p>(<b>a</b>) The normalized electrical resistance versus normalized temperature. Note the electronic configuration, and 3-d and 4-d states of Ni and Pd, respectively, and the order-disorder transition for Ni at <math display="inline"> <semantics> <msub> <mi>T</mi> <mi>c</mi> </msub> </semantics> </math>. Both Ni and Pd follow the same path above <math display="inline"> <semantics> <msub> <mi>T</mi> <mi>c</mi> </msub> </semantics> </math>. Adapted from [<a href="#B42-magnetochemistry-02-00022" class="html-bibr">42</a>]; (<b>b</b>) Schematic representation of the density of electronic states, N(E), of the 3-d transition FM metals. Note the N(E) is room temperature density of states of s and d states at the Fermi energy, <math display="inline"> <semantics> <msub> <mi>F</mi> <mi>E</mi> </msub> </semantics> </math>, level. At <math display="inline"> <semantics> <msub> <mi>F</mi> <mi>E</mi> </msub> </semantics> </math>, the majority spin states (<span class="html-italic">i.e.</span>, spin-ups, ↑) are completely filled while the minority spin states (<span class="html-italic">i.e.</span>, spin-downs, ↓ ) are partially filled, and the unequal filling of bands is the main source of net magnetic moment in 3-d transition FM metals [<a href="#B98-magnetochemistry-02-00022" class="html-bibr">98</a>]; (<b>c</b>) Schematic illustrating two-current model of Mott as applied to 3-d FM metals. The resistivity, <math display="inline"> <semantics> <mi mathvariant="sans-serif">ρ</mi> </semantics> </math> arising from the scattering of the 4-s electrons and 3-d electrons are denoted by <math display="inline"> <semantics> <msub> <mi mathvariant="sans-serif">ρ</mi> <mrow> <mi>s</mi> <mi>s</mi> </mrow> </msub> </semantics> </math> and <math display="inline"> <semantics> <msub> <mi mathvariant="sans-serif">ρ</mi> <mrow> <mi>s</mi> <mi>d</mi> </mrow> </msub> </semantics> </math>, respectively. The plus and minus signs indicate spin-up and spin-down, respectively [<a href="#B98-magnetochemistry-02-00022" class="html-bibr">98</a>].</p> Full article ">Figure 6
<p>(<b>a</b>) Cross-sectional view of a FM/NM multilayer and the scattering of the 4-s conduction electrons (small black arrows crossing the yellow circles) by the local 3-d magnetic moments (big red arrows) (<b>a-i</b>) H = 0; (<b>a-ii</b>) H ≠ 0. The black diagonal arrows represent scattering paths of the 4-s conduction electrons. (<b>b</b>) Mott’s two-current model applied to multilayers: (<b>b-i</b>) H = 0; and (<b>b-ii</b>) H ≠ 0. Black arrows in (<b>b-i, ii</b>) represent current channels [<a href="#B98-magnetochemistry-02-00022" class="html-bibr">98</a>].</p> Full article ">Figure 7
<p>(<b>a</b>) Randomly-oriented multi-domains ferromagnetic (FM) multilayers, consisting of isotropic domain of Co; and (<b>b</b>) uniaxially oriented single domain FM multilayers [<a href="#B98-magnetochemistry-02-00022" class="html-bibr">98</a>].</p> Full article ">Figure 8
<p>(<b>a</b>) Schematics of biosensing scheme. It consists of giant magnetoresistance (GMR) sensor, which is developed underneath the substrate, bio-conjugated nano-magnetic particles embedded in the cell, antibody, and receptor. The dotted line shows the direction of stray magnetic fields induced by magnetically labeled bio-material (<b>b</b>) Microgram of the post-processed die and scanning electron microscopy images of the spin-valve biosensor array. Adapted from [<a href="#B154-magnetochemistry-02-00022" class="html-bibr">154</a>].</p> Full article ">Figure 9
<p>An Everspin spin-transfer-torque based magnetic random access memory chip for caching application. Reproduced with permission from [<a href="#B80-magnetochemistry-02-00022" class="html-bibr">80</a>], Copyright IEEE, 2014.</p> Full article ">Figure 10
<p>(<b>a</b>) Measurement configuration of magnetic tunnel junction, MTJ, and spin-transfer torque, STT, nanopillars-based Nano-oscillator, and magnetic, H field and current, I sign conventions; (<b>b</b>) differential magnetoresistance plotted against the H field; Inset shows the enlarged view at the low H field range. Reproduced with permission from [<a href="#B169-magnetochemistry-02-00022" class="html-bibr">169</a>], Copyright Nature Publishing Group, 2009; (<b>c</b>) Flow chart showing various features of a STT Nano-oscillator.</p> Full article ">Figure 11
<p>(<b>a-i</b>) Surface plasmon resonance (SPR) and (<b>a-ii</b>) magneto-optic SPR (MO-SPR) effects. Both the SPR and MO-SPR peaks shift towards higher incident angle, <math display="inline"> <semantics> <mi mathvariant="sans-serif">θ</mi> </semantics> </math>, with refractive index, <math display="inline"> <semantics> <msub> <mi>n</mi> <mi>d</mi> </msub> </semantics> </math>, of a sample. The sensing response of the MO-SPR configuration is much larger as compared to the sensing response of the SPR configuration for the same shift of refractive index, <math display="inline"> <semantics> <mrow> <mi mathvariant="sans-serif">δ</mi> <mi>n</mi> </mrow> </semantics> </math>. Adapted from [<a href="#B11-magnetochemistry-02-00022" class="html-bibr">11</a>]; (<b>b</b>) The MO-SPR versus <math display="inline"> <semantics> <mi mathvariant="sans-serif">θ</mi> </semantics> </math> for four types of samples: The <span class="html-italic">n</span> of the sample is increased from <math display="inline"> <semantics> <msub> <mi>n</mi> <mn>1</mn> </msub> </semantics> </math> = 1.7 to <math display="inline"> <semantics> <msub> <mi>n</mi> <mn>4</mn> </msub> </semantics> </math> = 2.0, in the increment of 0.1. The figure in the inset shows the MO-SPR sensitivity [<a href="#B177-magnetochemistry-02-00022" class="html-bibr">177</a>,<a href="#B178-magnetochemistry-02-00022" class="html-bibr">178</a>].</p> Full article ">
2772 KiB  
Article
1D Chains of Lanthanoid Ions and a Dithienylethene Ligand Showing Slow Relaxation of the Magnetization
by Mudasir Ahmad Yatoo, Goulven Cosquer, Masakazu Morimoto, Masahiro Irie, Brian K. Breedlove and Masahiro Yamashita
Magnetochemistry 2016, 2(2), 21; https://doi.org/10.3390/magnetochemistry2020021 - 31 Mar 2016
Cited by 14 | Viewed by 5118
Abstract
Three isostructural 1D lanthanoid complexes with the general formula {[Ln2(DTE)(H-DTE)(MeOH)2]·2H2O}n (Ln = Tb, Dy, and Yb; DTE = 1,2-bis(5-carboxyl-2-methyl-3-thienyl) perfluorocyclopentene) were synthesized. In the 1D chain structure of each complex, lanthanide ions are seven coordinate with [...] Read more.
Three isostructural 1D lanthanoid complexes with the general formula {[Ln2(DTE)(H-DTE)(MeOH)2]·2H2O}n (Ln = Tb, Dy, and Yb; DTE = 1,2-bis(5-carboxyl-2-methyl-3-thienyl) perfluorocyclopentene) were synthesized. In the 1D chain structure of each complex, lanthanide ions are seven coordinate with a capped trigonal prism geometry. The 1,2-bis(5-carboxyl-2-methyl-3-thienyl) perfluorocyclopentene (DTE) ligand adopts a parallel configuration in these complexes, which results in the loss of the photo-isomerization ability of the ligand. From magnetic measurements, each complex undergoes slow relaxation of the magnetization via multiple processes in a dc field. Full article
(This article belongs to the Special Issue Magnetic Anisotropy)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Photochromic 1,2-bis(5-carboxyl-2-methyl-3-thienyl) perfluorocyclopentene (DTE) ligand with two carboxylic groups in the open and closed form. Asymmetric carbon atoms are noted with a * mark.</p> Full article ">Figure 2
<p>(<b>a</b>) <span class="html-italic">Oak Ridge Thermal Ellipsoid Plot</span> (ORTEP) view of the asymmetric unit of 1 with thermal ellipsoids drawn at 30% probability. H atoms are omitted for clarity. Tb, MeOH and H<sub>2</sub>O have an occupancy of ½. (<b>b</b>) View of the 1D chain.</p> Full article ">Figure 3
<p>Temperature dependence of χ<span class="html-italic">T</span> for poly-crystalline samples of complexes 1, 2 and 3.</p> Full article ">Figure 4
<p>Normalized Argand plot for (<b>a</b>) 1 in a dc field of 5000 Oe; (<b>b</b>) 2 in a dc field of 2500 Oe and (<b>c</b>) 3 in a dc field of 2000 Oe. Point represent experimental data, and the lines were fitted to the data.</p> Full article ">Figure 5
<p>Relaxation time (τ) <span class="html-italic">vs. T</span> for the three complexes. The lines represent the best fits obtained by using Equation S5.</p> Full article ">
2269 KiB  
Article
Spin Transition Kinetics in the Salt [H2N(CH3)2]6[Fe3(L)6(H2O)6] (L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate)
by Cristina Sáenz de Pipaón, Pilar Maldonado-Illescas, Verónica Gómez and José Ramón Galán-Mascarós
Magnetochemistry 2016, 2(2), 20; https://doi.org/10.3390/magnetochemistry2020020 - 28 Mar 2016
Cited by 9 | Viewed by 5511
Abstract
The dimethylammonium salt of the FeII polyanionic trimer [Fe3(μ-L)6(H2O)6]6− (L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate) exhibits a thermally induced spin transition above room temperature with one of the widest hysteresis cycles observed in a spin crossover [...] Read more.
The dimethylammonium salt of the FeII polyanionic trimer [Fe3(μ-L)6(H2O)6]6− (L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate) exhibits a thermally induced spin transition above room temperature with one of the widest hysteresis cycles observed in a spin crossover compound (>85 K). Furthermore, the metastable high-spin (HS) state can be thermally trapped via relatively slow cooling, remaining metastable near room temperature, with a characteristic TTIESST = 250 K (TIESST = temperature-induced excited spin-state trapping). The origin for this unique behavior is still uncertain. In this manuscript, we report detailed studies on the relaxation kinetics of this system in order to disclose the mechanism and cooperativity controlling this process. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) Molecular structure of [Fe<sub>3</sub>(μ-L)<sub>6</sub>(H<sub>2</sub>O)<sub>6</sub>]<sup>6−</sup> (only the triazole group from the ligands is represented for clarity); (<b>b</b>) hydrogen bonding connectivity between multiple trimers in 1; (<b>c</b>) X-ray diffraction powder pattern for 1 at room temperature as powder (green), single crystals (black), and after magnetic measurements in the 2–400 K; (<b>d</b>) temperature dependence of the X-ray diffraction powder pattern for 1 in the 300–420 K range at a scan rate of 1 K min<sup>−1</sup>.</p> Full article ">Figure 2
<p>(<b>a</b>) χ<span class="html-italic">T vs. T</span> plots for 1 at different heating/cooling rates; (<b>b</b>) relaxation of the trapped high spin (HS) HS-HS-HS fraction at different temperatures in the 265–235 K range; after cooling down, the sample at 10 K/min from saturation value at 400 K.</p> Full article ">Figure 3
<p>Fitting of the relaxation curves for the trapped HS-HS-HS fraction of 1 at different temperatures to exponential or sigmoidal expressions: (<b>a</b>) 265 K, (<b>b</b>) 260 K, (<b>c</b>) 255 K, (<b>d</b>) 250 K, (<b>e</b>) 245 K, (<b>f</b>) 240 K and (<b>g</b>) 235 K; (<b>h</b>) variation of <span class="html-italic">k</span><sub>HL</sub> as a function of <span class="html-italic">T</span><sup>−1</sup>.</p> Full article ">Figure 4
<p>Fitting of the Low spin (HS-LS-HS) to High Spin (HS-HS-HS) transition for 1 at different temperatures to exponential expression.</p> Full article ">
3679 KiB  
Article
Vibrational Coupling of Nearest Neighbors in 1-D Spin Crossover Polymers of Rigid Bridging Ligands. A Nuclear Inelastic Scattering and DFT Study
by Juliusz A. Wolny, Isabelle Faus, Jennifer Marx, Rudolf Rüffer, Aleksandr I. Chumakov, Kai Schlage, Hans-Christian Wille and Volker Schünemann
Magnetochemistry 2016, 2(2), 19; https://doi.org/10.3390/magnetochemistry2020019 - 25 Mar 2016
Cited by 13 | Viewed by 6171
Abstract
The nuclear inelastic scattering signatures of the low-spin centers of the methanosulphonate, tosylate, and perchlorate salts of the spin crossover polymer ([Fe(II)(4-amino-1,2,4-triazole)3]2+)n have been compared for the low-spin phase, for the mixed high-spin and low-spin phases, as well [...] Read more.
The nuclear inelastic scattering signatures of the low-spin centers of the methanosulphonate, tosylate, and perchlorate salts of the spin crossover polymer ([Fe(II)(4-amino-1,2,4-triazole)3]2+)n have been compared for the low-spin phase, for the mixed high-spin and low-spin phases, as well as for Zn(II) diluted samples. Within this series a change in the vibrational pattern in the 320–500 cm−1 region is observed. Significant shifts and decreasing intensity of bands at ~320 cm−1 and bands over 400 cm−1 are observed as the molar fraction of the low-spin (LS) centers decrease. Density functional theory calculations using Gaussian09 (B3LYP/CEP-31G) for pentameric, heptameric, and nonameric model molecules yielded the normal modes of several spin isomers: these include the all high-spin (HS) and the all low-spin (LS) configuration but also mixtures of LS and HS centers, with a special focus on those with LS centers in a HS matrix and vice versa. The calculations reproduce the observed spectral changes and show that they are caused by strain extorted on a LS Fe(II) center by its HS neighbors due to the rigid character of the bridging aminotriazole ligand. Additionally, the normal mode analysis of several spin isomers points towards a coupling of the vibrations of the iron centers of the same spin: the metal-ligand stretching modes of the all LS and the all HS spin isomers reveal a collective character: all centers of the same spin are involved in characteristic normal modes. For the isomers containing both LS and HS centers, the vibrational behavior corresponds to two different subsets (sublattices) the vibrational modes of which are not coupled. Finally, the calculation of nuclear inelastic scattering data of spin isomers containing a ca. 1:1 mixture of HS and LS Fe(II) points towards the formation of blocks of the same spin during the spin transition, rather than to alternate structures with a HS-LS-HS-LS-HS motif. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Experimental pDOS of (<b>1</b>) obtained at 80 K (<b>a</b>); of (<b>2</b>) at 273 K (<b>b</b>); and of (<b>3</b>) at 80 K (<b>c</b>). Reprinted from [<a href="#B32-magnetochemistry-02-00019" class="html-bibr">32</a>].</p> Full article ">Figure 2
<p>Left: Experimental pDOS of (<b>1</b>) (pure LS phase) (<b>a</b>) and calculated pDOS involving modes of all LS centers for the pentameric (<b>b</b>); heptameric (<b>c</b>); and nonameric (<b>d</b>) model molecules displayed in <a href="#magnetochemistry-02-00019-f006" class="html-scheme">Scheme 1</a>. Right: Simulated pDOS of only the central LS Fe(1) (red) calculated with the pentameric (<b>e</b>); heptameric (<b>f</b>) and nonameric (<b>g</b>) model molecules. The bars denote the calculated vibrational modes scaled to 1/5 of their calculated intensity. The iron centers for which the pDOS has been calculated are marked in bold.</p> Full article ">Figure 3
<p>Left: Experimental pDOS of (<b>3</b>) (<span class="html-italic">ca.</span> 1:1 mixture of LS and HS Fe(II) centers, diluted in Zn(II) matrix) (<b>a</b>) and DFT simulations involving modes of all but the terminal centers for pentameric (<b>b</b>); heptameric (<b>c</b>); and nonameric (<b>d</b>) model molecules with LS Fe(II) in center and all HS neighbors. Right: Simulated pDOS of only the central LS Fe(1) (red) calculated with the pentameric (<b>e</b>); heptameric (<b>f</b>); and nonameric (<b>g</b>) model molecules. The centers taken for a given calculations of pDOS are marked in bold. The bars denote the calculated vibrational iron modes scaled to 1/5 of their calculated intensity. The most intensive iron vibration of the heptameric and nonameric model are truncated for clarity reasons. The calculations shown left involved all HS Fe(II) neighbors, although the spectrum was taken for the Zn(II) diluted sample; therefore, the intensity of the bands at 200–300 cm<sup>−1</sup> due to the HS vibrations is overestimated.</p> Full article ">Figure 4
<p>Comparison of the experimental pDOS of (<b>2</b>) at 273 K (<b>a</b>) with the calculated pDOS of the chessboard (<b>b</b>,<b>c</b>) and block models (<b>d</b>–<b>f</b>). The bars denote the calculated vibrational iron modes scaled to 1/5 of their calculated intensity. Note that the applied models have a LS:HS ratio of 3:2, 2:3, and 4:3, rather than an exact 1:1 ratio.</p> Full article ">Figure 5
<p>Calculated pDOS for HS Fe(1) (bold, highlighted blue) in HS (<b>top</b>) and LS (<b>bottom</b>) matrix for pentameric (<b>left</b>), heptameric (<b>middle</b>), and nonameric (<b>right</b>) models. The bars denote the calculated vibrational iron modes scaled to 1/5 of their calculated intensity.</p> Full article ">Figure 6
<p>Trimeric Fe<sub>3</sub>(atrz)<sub>6</sub>(H<sub>2</sub>O)<sub>6</sub>Cl<sub>6</sub> (<b>a</b>); pentameric Fe<sub>5</sub>(atrz)<sub>12</sub>(H<sub>2</sub>O)<sub>6</sub>Cl<sub>6</sub> (<b>b</b>); heptameric Fe<sub>7</sub>(atrz)<sub>18</sub>(H<sub>2</sub>O)<sub>6</sub>Cl<sub>6</sub> (<b>c</b>); and nonameric Fe<sub>9</sub>(atrz)<sub>24</sub>(H<sub>2</sub>O)<sub>6</sub>Cl<sub>6</sub> (<b>d</b>) model molecules used in calculations in [<a href="#B28-magnetochemistry-02-00019" class="html-bibr">28</a>] (trimeric and pentameric) and in this study (heptameric and nonameric). In each case, the two terminal iron centers, with three coordinated waters are assumed to be in the high-spin state. All other centers may be either low-spin (denoted as L) or high-spin (denoted as H). Thus, for example, for the pentameric model five spin isomers are possible, denoted as HHHHH, HLLLH, HHLHH, HLHLH and HHLLH (identical with HLLHH). The iron in the inversion center is denoted as Fe(1), the next centrosymmetrically related ones are denoted as Fe(2)/Fe(2’), Fe(3)/Fe(3’), <span class="html-italic">etc.</span></p> Full article ">
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
 
Displaying articles 1-9
Previous Issue
Next Issue
Back to TopTop