JPH0544089B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a magnetoresistive read head using a current bias method.

[Background of the invention]

Conventionally, in a magnetoresistive read head using a magnetoresistive element, in order to improve the linearity of the magnetoresistive element, a bias conductor is provided close to the magnetoresistive element, and a bias current is applied to the bias conductor. It is known that a bias magnetic field is generated by flowing a magnetic field, and this bias magnetic field is applied to a magnetoresistive element (for example,
JP-A-58-182125, JP-A-59-19222).

By the way, it is known that Barkhausen noise is generated in such a magnetoresistive reproducing head, which causes waveform distortion in the reproduced signal. This Barkhausen noise is generated when a plurality of magnetic domains are generated in the magnetoresistive element, and the domain walls of these magnetic domains irreversibly move due to changes in the intensity of the external magnetic field.

Preventing the occurrence of this Barkhausen noise 1
One known method is to add a return magnetic path to the magnetoresistive element to suppress the generation of domain walls (for example, Japanese Patent Laid-Open No. 58-220241
Publication No. 59-56210, Japanese Patent Application Laid-open No. 51-1983
112320), the generation of domain walls also depends on the film formation conditions and patterning shape of the magnetoresistive element, and it is extremely difficult to completely eliminate domain walls.

For this reason, Barkhausen noise cannot be avoided in conventional magnetoresistive read heads.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art,
An object of the present invention is to provide a magnetoresistive effect type reproducing head which can sufficiently suppress Barkhausen noise.

[Summary of the invention]

The magnetoresistive effect is caused by the interaction between the current flowing through the element and the spin, and there is no direct involvement of the domain walls that occur in the element, and the rotation of the spin sufficiently follows changes in the external magnetic field. For,
Since the moving speed of the domain wall is sufficiently slow, it is not possible to move following sudden changes in the external magnetic field. Therefore, when the external magnetic field changes rapidly, irreversible movement of the domain wall does not occur, and Barkhausen noise does not occur.

The present invention has been made in view of this point, and in order to achieve the above object, the bias magnetic field is changed at a speed sufficiently faster than the moving speed of the domain wall, and the domain wall in the magnetoresistive element is irreversible. It is distinctive in that it suppresses physical movement.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a magnetoresistive read head according to the present invention, in which 1 is a magnetoresistive element (hereinafter referred to as an MR element), 2 is an insulator, 3 is a bias conductor, and 4a , 4b are connection terminals for the bias conductor 3, 5a and 5b are connection terminals for the MR element 1, 6a to 6d are lead wires, 7 is a high frequency bias current circuit, 8 is an MR element current circuit, 9 is a preamplifier, and 10 is a detection rectifier. In the circuit, 11 is an output terminal.

In the figure, the bias conductor 3 is provided close to the MR element 1 via the insulator 2, and is connected to the high frequency bias circuit 1 through the lead wire 6d, the connection terminal 4b, the bias conductor 3, the connection terminal 4a, and the lead wire. A high frequency bias current I _b shown in FIG. 2a flows through the bias conductor 6a, and a bias magnetic field of the MR element 1 is generated in the bias conductor 3. In this case, the arrangement of the bias conductor with respect to the MR element 1 is set so that the bias magnetic field rotates the magnetization of the MR element 1 in its width direction, that is, in a direction orthogonal to the connecting terminals 5a and 5b.

On the other hand, the lead wire 6c from the MR element current circuit 8,
The direct current shown in Figure 2b passes through the connecting terminal 5b, MR element 1, connecting terminal 5a and lead wire 6b.
I _MR is played. The MR element 1 has a bias conductor 3
A signal magnetic field from a recording medium on which an information signal (not shown) is recorded is applied together with the bias magnetic field generated by the MR element 1, and the resistance value of the MR element 1 changes in accordance with these magnetic fields. A reproduction signal that changes according to the change in resistance value is supplied to a preamplifier 9, amplified there, and then rectified and detected by a detection rectifier circuit 10 to obtain a desired information signal at an output terminal.

High frequency bias current I _b flowing through bias conductor 3
is a current that alternately changes the current values I _b1 and I _b2 at high speed, as shown in Fig. 2a, and its rise,
The falling edge is set steeply. The frequency of this high-frequency bias current is set to be sufficiently faster than the response speed of the domain wall of the MR element 1, and if it is 100 kHz or more, irreversible movement of the domain wall can be suppressed, but in order to have a sufficient margin, it is necessary to set the frequency to 500 kHz or more. A range of 1MHz is preferred.

FIG. 3 is an operating curve showing the change in resistance value Δρ of the MR element 1 with respect to the input magnetic field H. Its operating point is H _Ib1 when the current value of high-frequency bias current I _b is I _b1 , and H _Ib2 when the current value is I _b2 , and as the bias current I _b changes, these operating points H _Ib1 ,
Take H _Ib2 alternately. The signal magnetic field H _s is superimposed on the bias magnetic field caused by this high-frequency bias current I _b , and as the output signal of the MR element 1 (that is, the input signal of the preamplifier 9), the envelope represents the information signal to be reproduced, and the high-frequency bias Current I _b
is a high-frequency signal I _s with the same frequency as . This high frequency signal _Is is amplified by a preamplifier 9, detected and rectified by a detection rectifier circuit 10, and a necessary information signal is obtained at an output terminal 11.

At this time, due to the high frequency bias magnetic field, the MR
In the element 1, there is no movement of the domain walls, and therefore, the information signal obtained at the output terminal 11 does not suffer from waveform distortion due to Barkhausen noise.

Further, among the operating points _HIb1 and _HIb2 in FIG. 2a, the deep operating point _HIb1 is set at a point where the magnetization direction of the MR element 1 is in the width direction and the magnetic domain almost disappears. By doing so, the shallow operating point
The operation up to H _Ib2 is only the rotation of the spin, thereby making it possible to suppress Barkhausen noise more reliably.

It goes without saying that the sensitivity is increased by setting the operating point H _Ib2 at a position where the slope of the Δρ-H curve is steep.

FIG. 4 is a block diagram showing another embodiment of the magnetoresistive reproducing head according to the present invention, in which reference numeral 12 indicates a magnet, and parts corresponding to those in FIG. Omitted.

In this embodiment, a magnet 12 is placed close to the MR element 1.
As shown in FIG. 5a, the high-frequency bias current _Ib is set to only an alternating current component, and as shown in FIG. 6, an operating curve similar to that in FIG. 3 is obtained. The current decreases, reducing power consumption and preventing heat generation in the bias conductor 3.

Incidentally, assuming that the operating point of the magnet 12 is H _Ib1 in FIG. 6, the high frequency bias current I _b is only in the negative direction.

FIG. 7 is a block diagram showing still another embodiment of the magnetoresistive type reproducing head according to the present invention.
3 is a synchronous detection circuit, and parts corresponding to those in FIG. 1 are given the same reference numerals.

This embodiment uses a synchronous detection circuit 15 in place of the detection rectifier circuit 10 in the embodiment shown in FIG.
is supplied from the high frequency bias current circuit 7.

The high frequency bias current _Ib may be offset as shown in FIG. 2a, or may not be offset as shown in FIG. 5a. In this embodiment, as shown in FIG. 8a, the high frequency bias current
The explanation will be based on the assumption that _Ib is not offset. It goes without saying that the current _IMR flowing through the MR element 1 is a direct current, as shown in FIG. 8b.

The operating curve of this embodiment is shown in FIG. In the same figure, the operating point due to high frequency bias current I _b is
H _Ib1 and H _Ib2 , and the output signal I _s of the MR element 1 represents the information signal sought by its thick envelope.

Therefore, in the synchronous detection circuit 13, the operating point is
By synchronously detecting the output signal I _s so that the output signal I _s is sampled when it reaches H _Ib2 ,
A desired information signal is obtained at the output terminal 11.

Also in this embodiment, since the magnetization process of the MR element 1 is only the rotation of spins due to the high-frequency bias magnetic field, no irreversible movement of the domain wall occurs in the MR element 1, and therefore Barkhausen noise can be suppressed.

FIG. 10 is a block diagram showing still another embodiment of the magnetoresistive reproducing head according to the present invention,
14 is a high frequency current circuit, and parts corresponding to those in FIG. 1 are given the same reference numerals.

In contrast to the previous embodiments in which a direct current was supplied to the MR element 1, this embodiment supplies a high-frequency current I _MR (Fig. 11) synchronized with a high-frequency bias current I _b (Fig. 11a). b) is supplied to the MR element 1. For this purpose, a high frequency current circuit that is synchronously controlled by a synchronizing signal S from a high frequency bias current circuit 7 is used as a current source for the MR element 1. As a result, this embodiment also has the same synchronous detection function as the embodiment shown in FIG.

Since the synchronous detection function is thus provided, the operating point of the high frequency bias can be set in the same way as the operating point of any of the embodiments shown in FIG. 1, FIG. 4, or FIG. Therefore, Barkhausen noise can be suppressed.

Furthermore, since the current I _MR flowing through the MR element 1 is a high-frequency signal, its duty is 0.5 compared to 1 for direct current, and the amount of heat generated by the MR element 1 is 1 compared to 1 for direct current. /Can be reduced by 2 times.
Therefore, in this embodiment, it is possible to reduce not only Barkhausen noise but also thermal noise. Furthermore, by adjusting the high frequency current circuit 14, it is possible to change the duty of the current I _MR flowing through the MR element 1, and the smaller this duty is, the lower the amount of heat generated can be. In this case, by reducing the duty of the current I _MR , the peak value of the current I _MR can be correspondingly increased, so that the sensitivity can be further increased.

〔Effect of the invention〕

As explained above, according to the present invention, irreversible movement of the magnetic domain wall of a magnetoresistive element can be suppressed, so generation of Barkhausen noise can be prevented, and the drawbacks of the above-mentioned conventional techniques can be avoided. A magnetoresistive reproducing head with excellent functionality can be provided.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of a magnetoresistive read head according to the present invention, FIGS. 2a and 2b are waveform diagrams showing the bias current in FIG. 3 is an operating curve diagram of the magnetoresistive element shown in FIG. 1, FIG. 4 is a block diagram showing another embodiment of the magnetoresistive read head according to the present invention, and FIGS. 5a and 5b are respectively shown in FIG. 4. FIG. 6 is a waveform diagram showing the bias current and current flowing through the magnetoresistive element, FIG. 6 is an operation curve diagram of the magnetoresistive element in FIG. 4, and FIG. 8a and 8b are waveform diagrams showing the bias current in FIG. 7 and current flowing through the magnetoresistive element, respectively. FIG. 9 is an operating curve diagram of the magnetoresistive element in FIG. 7. , FIG. 10 is a block diagram showing still another embodiment of the magnetoresistive reproducing head according to the present invention, and FIGS. 11a and 11b are waveforms showing the bias current and current flowing through the magnetoresistive element in FIG. 10, respectively. It is a diagram. 1... Magnetoresistive element, 3... Bias conductor, 7... High frequency bias circuit.

Claims (1)

[Claims] 1. A bias conductor is provided close to the magnetoresistive element, a bias current is passed through the bias conductor to generate a bias magnetic field, and the bias magnetic field causes
In the magnetoresistive playback head configured to set the operating point of the magnetoresistive element, a high frequency bias current circuit is provided to make the bias current a high frequency current, and the change in the bias magnetic field caused by the high frequency current affects the magnetoresistive element. A magnetoresistive reproducing head characterized in that the frequency of the high-frequency current is set to such an extent that a domain wall in an effect element does not follow and move.