JPS5933616A - Thin film magnetic head - Google Patents

Abstract

PURPOSE:To obtain a thin film magnetic head which is free from deterioration of S/N, by using one of three terminals provided to an MR (magneto-resistance) element as a common terminal with one of other two terminals grounded via a resistance and supplying a fixed current from the last terminal. CONSTITUTION:Three terminals 7-9 are provided to an MR element. The terminal 9 is AC-earthed via a capacitor 15, and the terminal 8 is grounded via a resistance 13. Then MR currents 10 and 11 are supplied from a constant current source circuit 12 via terminals 7 and 8 and the resistance 13. Then resistance value of an MR element 6 varies with a signal magnetic field given from a magnetic recording medium. Then the potential is reduced between terminals 7 and 9 with reduction of the resistance of the element 6 since the MR current is constant. In this case, the potential variation of the terminal 7 is twice as much as that of the terminal 9. The reproduction output emerging at the terminal 7 has a phase opposite to that of the terminal 9. The outputs emerging at terminals 7 and 8 are supplied to a differential amplifier 14 via a capacitor to obtain an output of reproduction from the element 6. As a result, it is possible to obtain an output of reproduction which is free from an effect of external noises.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thin film magnetic head used for recording and reproducing digital signals.

Conventional structure and its problems The conventional magnetoresistive head used for reproducing digital signals, etc., is perpendicular to the recording medium 1 (
A magnetoresistive element (hereinafter referred to as an MR element), which is a strip-shaped ferromagnetic thin plate, is brought into contact with or close to the M
Electrodes 3.4 are arranged at both ends of the R element 2 in the longitudinal direction (Z direction), a constant current i is passed between the electrodes 3 and 4, and the resistance value in the X direction is determined by the signal magnetic field of the recording medium 1 in the Y direction. Changes were detected by voltage changes between electrodes 3 and 4.

Generally, a magnetoresistive head for reproduction is built into the same deck as an inductive thin film magnetic head for recording, or is deposited on the same substrate, and is used in close proximity to the inductive thin film magnetic head for recording. At this time, since the recording current leaks into the reproduction output (feedthrough), it becomes impossible to reproduce the data signal with simultaneous monitoring that reproduces the recorded signals at the same time. In addition, in order to reduce feedthrough or to perform short wavelength reproduction, when applying bias using an external magnet in a shield type head that has a magnetic gap on both sides of the MR element,
If it is shielded, apply a sufficient magnetic field to the MR element.
A large external magnetic field is required to achieve this, and as a result, the signals recorded on the medium are demagnetized, and the shielding effect is not sufficient to prevent field-through, making simultaneous monitoring during recording difficult and impractical. As a countermeasure against such field through, in order to record and reproduce the same data by distributing it to multiple tracks, the following signal processing is performed, and during playback, the sum signal of the output from the even-numbered track and the odd-numbered track are combined. By obtaining the subtraction output from the sum signal of the output from the track, the in-phase feed is superimposed on the head wiring.
This is a method of canceling out the effects of toss-through or noise.

In this method, in order to record and reproduce the same signal on multiple tracks, it is necessary to have recording heads and reproduction heads that are multiple times (at least twice) the number of signals, resulting in a poor head manufacturing yield. There is a problem in that the number of henode wires increases.

In order to overcome this problem, there is a method in which the structure of the reproducing head is realized by the shunt bias method, instead of using a plurality of tracks for recording one data as described above. The shunt bias method, which is one structure of the current bias method, is a shield type applied for reproducing short wavelengths, and this is shown in FIGS. 2(a) and (b). It has three terminals 21, 22, and 23 including a common ground terminal 21, and the MR element 24 has r.

A bias magnetic field is applied to the MR element 24 by a current flowing through this resistance element 25. A constant current i is applied to the other two terminals of the MR element 24 from a constant current source circuit 26 and 27 so as to flow into the common ground terminal 21, and a bias magnetic field HB in the opposite direction is applied to the MR element 24 from the outside. Added from. M is the magnetization direction of the MR element 24. When a signal magnetic field is input to the MR element 24 maintained in such a state, the signal magnetic field is generated in such a way that the two parts of the MR element 24 with the common booth terminal 21 in between have opposite current directions. Therefore, it is magnetized as a reverse phase. When taking the difference signal between the voltages output to the two electrodes, in the shunt bias method the output is generally under biased, but even if one output is under biased and the reproduced output is distorted, it will not interact with the other output. Since the distortion component is canceled out and compensated for, the playback output is good, and external noise is also canceled out. demanding and impractical when compared to other heads. The trick is to pass current through both the MR element and the resistance element. First, it has the disadvantage that it generates more thermal noise, which is unique to MR elements.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks, and provides a thin film magnetic head that allows easy azimuth adjustment and does not generate any appreciable thermal noise.

Structure of the Invention The present invention provides an MR element with three terminals, one of which is used as a common terminal as a comparison electrical connection, this common terminal is grounded in an alternating current manner, and one of the other two terminals is connected via a resistor. By grounding the terminal and supplying a constant current from the other terminal to obtain a reverse-phase reproduction output, this is differentially amplified to eliminate the influence of external noise that enters the head and the wiring from the head. By using induced magnetic anisotropy as a method, it is possible to remove mutual interference between the medium and thin film head, that is, demagnetization of the medium, and thermal noise peculiar to MR heads, thereby reducing the deterioration of the signal-to-noise ratio. Not a good head.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The structure of the MR-\node of the present invention is υ↓, as shown in FIG. 1, in which an MR element is provided with three terminals. MR element 6
MR current supply and regeneration 1 sled 3
Two terminals 7, 8.9 are provided, and terminal 9 of these terminals is grounded via a capacitor 16, that is, AC grounding is performed.

If there are a large number of MR elements 6, the number of terminals for wiring can be reduced by making these ends 7-9 common and taking them out as a common terminal and connecting them to AC grounding. Terminal 8 is grounded via resistor 13. The resistance value of this resistor 13 is set to be the same as the equivalent output impedance of the constant current source circuit 12 connected to the terminal 7. From the constant current source circuit 12, terminals 7 to 8. resistance 1
The MR current 10.11 flowing through 3 to the ground side is supplied. The end r9 is only connected to AC ground, so is it an MR power line?
4U10.11 tri, exactly the same. Then, a bias magnetic field in the same direction is applied to the MR element r-6 from the outside. 1viR element 6 due to the signal magnetic field from the magnetic recording medium.
When the magnetization direction M of MR changes and its resistance value changes, MR
Since the main current is a constant current, if the resistance value of MR element r-6 becomes small, the potential between terminals 7 and 9 will drop, but terminal 8 (/i
It is a constant potential. The variation in potential at terminal 7 is twice that at terminal 9.

As a result, the fluctuating voltage from terminal 7 to terminal 9, that is, the reproduced output appearing at terminal -f-7, and the fluctuating voltage from terminal 8 to terminal 9, that is, the reproduced output appearing at terminal 9, have exactly q opposite phases. A reproduced output from the MR element 6 can be obtained by supplying the positive and negative input voltages to the terminals 7 and 8, respectively, and performing differential amplification. Note that the same applies even if the direction of the MR main current is opposite to that described above.

By the way, since external noise such as recording current feed-through is alternating current, it is mixed into the head and the wiring from the head so that it flows toward the alternating current grounding side (lower impedance side). That is, the external noise mixed into the MR element and wiring on the terminal 7 side is in phase with the external noise mixed into the MR element and wiring on the terminal 8 side.

The minute signal 4 equivalent circuit d in the configuration shown in FIG. 3 is as shown in FIG.
is occurring. External noise 18Q, 1. Represented as en. The constant current source is expressed as a resistor 2o whose internal impedance is the same as that of the resistor 13.

On the other hand, there is a signal source 17 on the terminal 8 side of MR Soryo-6.
Generates a signal -e8 that is in opposite phase to the signal es on the terminal T side External noise 1'j &, J:☆ii4 en that is in phase with the f-8 side
It is expressed as Since the impedances of the l-end r-71111 system and the terminal 8 side system are the same, the external 7' noise becomes the same en on both the terminal 7 side and the terminal 8 side as described above.

As a result of the above, the signals from the two terminals are transferred to the differential amplifier 14.
By inputting to , the noise component will be canceled in the output and the signal component will be obtained as 206,
It is possible to obtain a reproduction output that is completely unaffected by external noise. Then, the resistance change of the MR element θ is common to the terminal 9.
Since the left and right elements are in phase with each other, variations in the output waveform with respect to the azimuth of the head C caused by the shunt bias method shown in FIG. 2 are not a problem in the present invention. Furthermore, since no extra current is applied to the tip of the element for the bias means, thermal noise due to Joule heat is reduced. Still, the present invention has the advantage that the circuit configuration is simple because only one constant current source is required.

In order to carry out the present invention more effectively, FIG. 6 shows another embodiment in which there is no demagnetization of the medium or generation of noise, that is, no deterioration of the signal S to noise N ratio. This figure 5 is MR
The difference between the side view of the element 6 and the embodiment shown in FIG. 3 is that the bias magnetic field of the MR element 6 is applied by external means such as an external magnet or electric current in the case shown in FIG. , in FIG. 5, the magnetization is oriented in the optimum bias direction by induced magnetic anisotropy. This induced magnetic anisotropy can be obtained as follows. That is, when the surface of the substrate on which the MR element 6 is deposited is polished in one direction with a lapping tape or the like, the roughness of the substrate surface follows the lapping streaks and becomes rough anisotropically in a certain direction.

Although the intervals between the lap marks are random, magnetic domains are generated along the wrap marks, and the magnetic domains are subdivided and have good orientation, resulting in a large induced magnetic anisotropy of +1-.

Due to the induced magnetic anisotropy as described above, MR
There is no need to apply a bias magnetic field to the element 6 by external means, there is no demagnetization of the medium, and it is possible to provide the MR element 6 with a head free of thermal noise due to heat generated by the bias current.

Effects of the Invention As described in Section 2, the present invention has a simple configuration, allows easy azimuth adjustment, and provides a thin film magnetic head that does not generate thermal noise, and its effects are significant. .

[Brief explanation of the drawing]

Figure 1, Figure 2 (a), and (b) are diagrams showing the conventional example, Figure 3.
The figure shows an embodiment of the present invention together with a circuit, FIG. 4 is an equivalent circuit diagram, and FIG. 5 is a side view of a magnetoresistive element of another embodiment. 6... Magnetoresistive element, 7,8.9...
・Terminal, 10.11...Current, 12...
・Constant current source circuit, 13... Resistor, 14...
・Differential amplifier, 16... Capacitor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 αυ Figure 5

Claims (1)

[Claims] A thin film magnetic head having a magnetoresistive element made of a ferromagnetic material deposited on a substrate, in which the magnetization of the magnetoresistive element is biased in a certain direction and a signal magnetic field is applied to the element. The common terminal at the center of the magnetoresistive element is grounded in an alternating current manner, one of the other two terminals is grounded via a resistor, and a constant current is supplied from the other terminal to connect the common terminal. A thin film magnetic head characterized in that it is configured to differentially extract changes in resistance between two other terminals as reproduction voltages.