RU2436859C2 - Semi-conducting ferrimagnetic material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: semi-conducting ferrimagnetic material is distinguished with constant value of saturation magnetisation at change of induction of magnetic field and contains iron, gallium and magnesium. It corresponds to homogenous solution of iron, gallium and magnesium oxides and has a formula: Mg(Fe_1-xGa_x)₂O₄, where x=0.05÷0.25. Homogeneity of solution is achieved with a method of self-propagating high temperature synthesis, while successive annealing of produced fine-dispersed amorphous material at temperature 1223÷1273 K and its cooling results in production of homogenous material with spinel structure.

EFFECT: production of semi-conducting ferrimagnetic material possessing constant value of saturation magnetisation at change of induction of magnetic field.

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Description

The invention relates to materials based on metal oxides, specifically to homogeneous polycrystalline materials based on complex metal oxides, specifically to a class of diluted spin-oriented magnets having semiconductor and ferrimagnetic properties, as well as high thermal stability of the product.

The invention can be used in spintronics, in which the leading role belongs not only to the electrical characteristic, but also to a quantum-mechanical one, such as the electron spin.

The development of spintronics is largely constrained by the lack of suitable materials that satisfy the following basic criteria:

- a constant magnitude of magnetization, a rectangular hysteresis loop and a small coercive force when changing the magnetic field induction;

- conservation of saturation magnetization at temperatures above 293 K;

- simplicity and reliability of methods for the synthesis of materials, the possibility of their structural inclusion in standard semiconductor circuits.

Magnetic semiconductor materials are usually divided into the following classes: Concentrated magnetic semiconductors (CMC); Semi-magnetic semiconductors (PMF); Inhomogeneous magnetic materials (NMM); Diluted magnetic semiconductors (RMP) and High-temperature ferromagnetic semiconductors (VTFP) [V.A. Ivanov et al. Spintronics and spintron materials. Russian Academy of Sciences, Chemical Series, 2004, No. 11, 2255-2303].

CMPs, which include EuO, Cr-chalcogenide spinels MeCr ₂ Xal ₄ , complex oxides BiMnO ₃ , CeCuO ₃ , YTiO ₃ , and pnictides Mn (Cr) As (Sb) have not received practical application due to low Curie temperatures and technological purity requirements for electronic materials. The same reasons, plus instability, impede the practical use of the PMF obtained on the basis of the matrices A ^II B ^VI and A ^IV B ^VI (A ^II - Zn, Cd, Hg; A ^IV - Pb, Sn; B ^VI - S, Se, Te), CdMnSe, PbSnMnTe, in which transition metal ions Fe ²⁺ , Mn ^2+, or Co ²⁺ randomly replace A-elements at the sites of the crystal lattice.

RMPs are materials in which III-V (III - Al, Ga, In; V - P, As, Sb) or II-IV (II - Zn, Cd; IV - Si, Ge, Pb semiconductors are used as matrices , Sn), in which the atoms of metals of groups II, III, and IV are statistically replaced by transition metal atoms with unfilled 3d-electron shells. Among the most studied RMPs are Ga _1-x Mn _x As material with x≤9-10 wt.% [AMNazmul, S. Sugahara and M. Tanaka, Phys. Rev., B, 2003, p. 67]. The disadvantage of these RMPs is the insufficiently high Curie temperatures (up to 172 K). The second drawback is the increase in the electrical resistance of the material with an increase in the manganese content, as well as high values of the coercive force and the absence of magnetic saturation and a rectangular hysteresis loop. Known RMP composition (ZnGa ₂ O ₄ ) _0.85 (Fe ₃ O ₄ ) _0.15 [ASRisbud et. al. Dilute ferromagnetic semiconductors in Fe-substituted spinel ZnGa ₂ O ₄ . J. Phys. Condens. Matter, 2005, v.17, p.1003-1010], the disadvantage of which is the insufficiently high Curie temperature (T _K is close to 200 K) and the large band gap (4.1 eV). The second disadvantage is the inhomogeneity of the material, which limits its use.

HTFs are CdGeP ₂ : Mn ₂ , ZnGeP ₂ : Mn, CdGeAs ₂ : Mn, ZnSiGeN ₂ : Mn materials with an averaged Mn / Cd or Zn≤20% ratio and paramagnetic transition temperatures of 300 ÷ 350 K. The disadvantage of such materials is the mismatch of the physicochemical characteristics of the WTPP with the initial semiconductor matrices and insufficiently high Curie temperatures. The second drawback of materials of this class is the dependence of the saturation magnetization on the magnitude of the applied external magnetic field and the high values of the coercive force, which imposes a limitation on the use of these materials in spintronics [A.S. Borukhovich. Physics of materials and structures of superconducting and semiconductor spin electronics // Ekaterinburg, Publishing House of the Ural Branch of the Russian Academy of Sciences, 2004, 175 pp.].

HMMs are composite materials containing as a matrix semiconductor oxides and particles of insoluble magnetic metals or oxides of Fe, Co and Ni. The disadvantage of such mixtures is their heterophase and irreproducibility of magnetic characteristics. The heterogeneity of the NMM is shown by the example of composites based on zinc and cobalt oxides Zn _1-X Co ²⁺ _X O, for which ferromagnetism is due to the presence of cobalt clusters [Jae Hyun Kim et al. Magnetic properties of epitaxially grown semiconducting Zn _1-X Co _X O thin films by pulsed laser deposition. J. Appl. Phys., 2002, v. 92, No. 10, p.6066-6071], [R. Rode et al. Magnetic semiconductors based on cobalt substituted ZnO. J. Appl. Phys., 2003, v. 93, No. 10, p. 7676-7678].

The above classes do not cover such an important property of magnetic semiconductor materials as the constancy of the saturation magnetization with a change in the magnetic field induction.

Closest to the claimed material is a composite material of the composition Mg (Fe _1-X Ga _X ) ₂ O ₄ class NMM [Pokrovsky B.I., Gapeev A.K., Goryaga A.N., Komissarova L.N. Crystal chemistry and magnetism of mixed gallium and indium-containing ferrites with spinel structure Ferrimagnetism // Moscow University Press, 1975, 208 pp.] (Prototype).

The disadvantages of the prototype is the heterogeneity of the material, which is confirmed by the dependence of the parameter of the crystal lattice on the composition.

The second disadvantage of the material is the pronounced dependence of the saturation magnetization on the value of the magnetic field induction.

The third disadvantage of Mg (Fe _1-X Ga _X ) ₂ O _{4 is} also the extremely high synthesis temperature of 1573 K, which imposes a restriction on the use of the material in the form of films on standard semiconductor substrates [S.M. ZI Physics of Semiconductor Devices. Translation from English edited by A.F. Trutko // M .: Energy, 1973, 656 p.].

The technical task is to find materials for which the saturation magnetization is constant with an accuracy of 10% in the operating temperature range of microelectronics from -60 to 175 ° C, which are also characterized by a high Curie temperature. This ensures the reliability of technological processes for the manufacture of electronic devices.

The invention is directed to the creation of a new class of magnetic semiconductor material - a class of diluted semiconductor spin-oriented ferrimagnets (RPSF) with constant saturation magnetization with a change in the magnetic field induction.

The technical result is achieved by the fact that a semiconductor ferrimagnetic material is proposed, characterized by a constant saturation magnetization with a change in the magnetic field induction, which includes iron, gallium and magnesium, is a homogeneous solution of iron, gallium and magnesium oxides and corresponds to the formula:

Mg (Fe _1-X Ga _X ) ₂ O ₄ ,

where x = 0.05 ÷ 0.25,

wherein the homogeneity of the solution is achieved by using the method of self-propagating high-temperature synthesis.

By ferrimagnetic is meant the state of a material in which the orientation of the spins of magnetic ions of different magnetic sublattices is antiparallel. At the same time, the sublattices themselves have magnetic moments of different magnitude, so that the total magnetization in the magnetically ordered state is nonzero.

Spin-oriented ferrimagnets are understood to mean a state in which there is no spatial reorientation of the electron magnetic moment and the associated change in the saturation magnetization of the material with a change in the magnetic field induction [Borukhovich AS Physics of materials and structures of superconducting and semiconductor spin electronics // Ekaterinburg: Publishing House of the Ural Branch of RAS. 2004, 175 p.].

The values of x are chosen from the considerations that for x <0.05, semiconductor properties do not appear, and for x> 0.25, the dependence of the saturation magnetization on changing the magnetic field induction is observed in the material.

The claimed material is obtained as follows. A solution containing a mixture of magnesium, gallium, iron nitrates and citric acid, where the molar ratio of metals Mg: Fe: Ga is 1: 2 (1-x): 2x at a given value of x in the range 0.05 ÷ 0.25, is evaporated by heating and constant stirring until a dense viscous mass is formed. An evaporated mixture of magnesium, gallium, iron and citric acid nitrates spontaneously ignites when a temperature of 500 K is reached [Sychev A.E., Merzhanov A.G. Self-propagating high-temperature synthesis of nanomaterials // Advances in Chemistry. 2004.V. 73. No. 2. S.157-170].

The obtained finely divided amorphous material is annealed in a muffle furnace at a temperature of 1223 ÷ 1273 K for 20 hours until a homogeneous material with a spinel structure is formed, followed by either cooling at a speed of 10 K per minute or quenching from temperatures of 1223 ÷ 1273 K.

The achievement of the technical result of the claimed invention is illustrated by the following attached illustrations and tabular data:

Figure 1. Dependences of saturation magnetization on magnetic field induction, on which curve 1 corresponds to the claimed material of MgFe _1.6 Ga _0.4 O ₄ composition, curve 2 to the material of MgFe _1.9 Ga _0.1 O ₄ composition, curve 3 to the material of MgFe _1.7 Ga _0.3 O ₄ composition and curve 4 - material composition MgFe _1.5 Ga _0.5 O ₄ , curve 5 corresponds to the material of the prototype composition MgFe _1.6 Ga _0.4 O ₄ .

Figure 2. Semiconductor characteristics of a material of the composition Mg (Fe _1-X Ga _X ) ₂ O ₄ , reflecting the spectral dependence of the square of optical absorption on the photon energy. Curve 1 corresponds to the composition of MgFe _1.6 Ga _0.4 O ₄ , curve 2 to the composition of MgFe _1.9 Ga _0.1 O ₄ , curve 3 to the composition of MgFe _1.7 Ga _0.3 O ₄ , curve 4 to the composition of MgFe _1.5 Ga _0.5 O ₄ .

Figure 3. Semiconductor characteristics of the material composition Mg (Fe _1-X Ga _X ) ₂ O ₄ , displaying the characteristic dependence of current strength on voltage. Curve 1 corresponds to the composition of MgFe _1.6 Ga _0.4 O ₄ , curve 2 to the composition of MgFe _1.9 Ga _0.1 O ₄ , curve 3 to the composition of MgFe _1.7 Ga _0.3 O ₄ , curve 4 to the composition of MgFe _1.5 Ga _0.5 O ₄ .

Figure 4. The homogeneity of materials with the composition Mg (Fe _1-X Ga _X ) ₂ O ₄ , reflecting the characteristic dependence of the crystal lattice parameter on the composition. Line 6 corresponds to the claimed material of the compositions Mg (Fe _1-X Ga _X ) ₂ O ₄ , and curve 7 to the material of the prototype Mg (Fe _1-X Ga _X ) ₂ O ₄ .

Figure 5. Thermal stability of a material of MgFe _1.6 Ga _0.4 O ₄ composition, characterized by a constant saturation magnetization, regardless of the cooling rate, curve 1a for a material obtained at a temperature of 1273 K with its subsequent cooling at a speed of 10 K per minute, curve 1b for a material obtained by quenching from a temperature of 1273 K.

6. X-ray diffraction pattern of the material with the composition MgFe _1.6 Ga _0.4 O ₄ , characterized by the presence of lines characteristic of spinel structures measured at 298 (1a) and 573 K (1c).

Table: "Curie temperatures for the claimed material according to examples 1-4."

The claimed semiconductor material has a constant saturation magnetization with a change in the magnetic field induction. As follows from Figure 1, the composition material MgFe _1.6 Ga _0.4 O _{4 is} characterized by a saturation magnetization value M = 28 ± 10% A · m ² · kg ^-1 , a rectangular hysteresis loop and a coercive force value H _C = 0.0188 ± 10% T., material composition MgFe _1.9 Ga _0.1 O ₄ - the saturation magnetization M = 20 ± 10% A · m ² · kg ^-1 , a rectangular hysteresis loop and the value of the coercive force H _C = 0,0085 ± 10% T., materials of MgFe _1.7 Ga _0.3 O ₄ and MgFe _1.5 Ga _0.5 O ₄ compositions - saturation magnetization M = 12 ± 10% A · m ² kg ^-1 , a rectangular hysteresis loop and coercive force H _C = 0.0095 ± 10% T.

As follows from curve 5 of Figure 1, for the material of the prototype, the magnitude of the saturation magnetization is not constant when changing the magnetic field induction. This indicates that in the crystal lattice of the heterophasic material of the prototype both ferrimagnetic and paramagnetic ordering exist simultaneously, that is, the material is not spin-oriented.

The claimed ferrimagnetic material has semiconductor properties, which are confirmed by the results of measurements of the band gap (Figure 2) and current-voltage characteristics (Figure 3). From the data of Figure 2 it follows that the band gap is characteristic of semiconductor materials. The same conclusion can be drawn on the basis of the non-linearity of the current-voltage characteristics in Fig. 3, while it was found that the material with the highest conductivity is MgFe _1.6 Ga _0.4 O ₄ .

The homogeneity of the material is confirmed by the results of x-ray phase analysis. From the data of Figure 4 it follows that the dependence of the parameter a of the hexagonal spinel lattice on the composition of the claimed material (6) is linear, which indicates its homogeneity. On the curve of the dependence of the lattice parameter on the compositions of the prototype (7) there are kinks indicating the heterogeneity of the material.

The claimed semiconductor ferrimagnetic material has high thermal stability, as indicated by the immutability of the saturation magnetization of the material (Figure 5) obtained in two different ways, as well as the results of XRD analysis of the material (Figure 6).

The claimed material has high Curie temperatures, the values of which are given in the Table.

Table No. of Example Material Composition Paramagnetic transition temperature (Curie temperature) T _K , (± 10) one MgFe _1.6 Ga _0.4 O ₄ 465 2 MgFe _1.9 Ga _0.1 O ₄ 650 3 MgFe _1.7 Ga _0.3 O ₄ 325 four MgFe _1.5 Ga _0.5 O ₄ 300

Below are examples of the receipt of the claimed material.

Example 1

As starting materials, solutions were used, the initial molar ratio of Mg: Ga: Fe metals in which corresponded to a ratio of 1: 1.6: 0.4. The composition of the starting materials was determined on the basis of TG analysis data (TGD 7000 thermal analyzer manufactured by ULVAC SINKU-RIKO, Japan). A solution containing a mixture of magnesium, gallium, iron nitrates and citric acid was evaporated with constant stirring until a dense viscous mass was formed. An evaporated mixture of magnesium, gallium, and iron nitrates spontaneously ignited at a temperature above 500 K. The obtained finely dispersed amorphous material was annealed at a temperature of 1273 K for 20 hours until a homogeneous material with a spinel structure was formed, followed by cooling either at a rate of 10 K per minute or quenching from a temperature of 1273 K The obtained semiconductor ferrimagnetic material corresponded to the formula MgFe _1.6 Ga _0.4 O ₄ (curve 1 in the illustrations).

Example 2

A solution containing a mixture of magnesium, gallium, iron nitrates and citric acid in a ratio of 1: 1.9: 0.1 was evaporated with constant stirring until a dense viscous mass was formed. An evaporated mixture of magnesium, gallium, iron, and citric acid nitrates spontaneously ignited at a temperature above 500 K. The obtained finely dispersed amorphous material was annealed at a temperature of 1273 K for 20 hours until a homogeneous material with a spinel structure was formed, followed by cooling at a rate of 10 K per minute. The obtained semiconductor ferrimagnetic material corresponded to the formula MgFe _1.9 Ga _0.1 O ₄ (curve 2 in the illustrations).

Example 3

A solution containing a mixture of magnesium, gallium, iron nitrate and citric acid in a ratio of 1: 1.7: 0.3 was evaporated with constant stirring until a dense viscous mass was formed. An evaporated mixture of magnesium, gallium, iron, and citric acid nitrates spontaneously ignited at a temperature above 500 K. The obtained finely dispersed amorphous material was annealed at a temperature of 1273 K for 20 hours until a homogeneous material with a spinel structure was formed, followed by cooling at a rate of 10 K per minute. The obtained semiconductor ferrimagnetic material corresponded to the formula MgFe _1.7 Ga _0.3 O ₄ (curve 3 in the illustrations).

Example 4

A solution containing a mixture of magnesium, gallium, iron nitrates and citric acid in a ratio of 1: 1.5: 0.5 was evaporated with constant stirring until a dense viscous mass was formed. An evaporated mixture of magnesium, gallium, iron, and citric acid nitrates spontaneously ignited at a temperature above 500 K. The obtained finely dispersed amorphous material was annealed at a temperature of 1223 K for 20 hours until a homogeneous material with a spinel structure was formed, followed by cooling at a rate of 10 K per minute. The obtained semiconductor ferrimagnetic material corresponded to the formula MgFe _1.5 Ga _0.5 O ₄ (curve 4 in the illustrations).

The materials presented by illustrations and tabular data were studied by X-ray diffraction (XRD), thermogravimetric (TG) and differential thermal (DTA) analyzes. X-ray diffraction analysis was performed using a DRON-3M diffractometer and a Guinier-de-Wolf monochromator camera. X-ray diffraction analysis of materials at 25 and 300 ° C was carried out on a Rigaku D / MAX 2200 high-temperature diffractometer (Japan). The spectra were processed using the Rigaku Application Data Processing software package.

On radiographs, only lines characteristic of homogeneous spinel structures were present.

TG analyzes were performed using a TGD 7000 thermal analyzer manufactured by ULVAK SINKU-RIKO, Japan.

According to the TG data, within the instrumental error of the device, the gross composition of the synthesized samples does not differ from the initial gross composition.

The study of magnetic and current-voltage characteristics was carried out on the installation "Liquid Helium Free High Field Measurement System (" Cryogenic LTD ", London, UK)."

The band gap was determined from diffuse scattering spectra: monochrome radiation (MDR-12, wavelength range 250–920 nm) was reflected from polycrystals on a sapphire holder and analyzed by a Hamamatsu-7680 computerized PMT.

The Curie temperature of the material was investigated by the ponderomotive method [V. Chechernikov. Magnetic measurements // Moscow: Moscow State University. 1969. 388 p.].

As can be seen from Figs. 1-6, tables and examples, the claimed product is a homogeneous semiconductor ferrimagnetic material of the class of diluted semiconductor spin-oriented ferrimagnets - RPSF, characterized by a constant saturation magnetization with a change in the magnetic field, Curie temperature T _K = 300 ÷ 650 K.

The unique combination of semiconductor and ferrimagnetic properties of the claimed material makes it a promising product for practical use in spintronics.

Claims (1)

A semiconductor ferrimagnetic material, characterized by a constant saturation magnetization when changing the magnetic field induction, which includes iron, gallium and magnesium, is a homogeneous solution of iron, gallium and magnesium oxides and corresponds to the formula
Mg (Fe _1-x Ga _x ) ₂ O ₄ ,
where x = 0.05 ÷ 0.25,
in this case, the homogeneity of the solution is achieved using the method of self-propagating high-temperature synthesis, and subsequent annealing of the obtained finely dispersed amorphous material at a temperature of 1223 ÷ 1273 K and its cooling leads to the formation of a homogeneous material with a spinel structure.

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