GB2281654A - A magnetoresistive head with thermal compensation - Google Patents

Abstract

A magnetoresistive head is provided, in which a bias layer 5 in the vicinity of a magnetoresistive element 7 is also used as a temperature detector for detecting the temperature change of the magnetoresistive element, and a signal thus detected is outputted through electrodes 10A, 10C. The level of the signal is corrected appropriately and subtracted from the output signal of the magnetoresistive element. In this way, the thermal asperity (Fig. 7, 72) is removed from the output signal of the magnetoresistive element. <IMAGE>

Description

MAGNETORESISTIVE HEAD MAGNETIC DISC APPARATUS The present invention relates to a magnetoresistive head (MR head), or more in particular to an MR head capable of removing the output fluctuations (thermal asperity) of the magnetoresistive head due to temperature variations such as frictional heating when the MR head is in contact with a magnetic recording medium.

An MR head using an MR element for reproduction has been suggested as a means for increasing the recording density of a magnetic disc. The MR element, the resistance of which changes with the magnetic field, is high in reproduction (playback) sensitivity as compared with the conventional inductive head. In reproduction mode, a constant current is applied to the MR element to detect the resistance change as a voltage change. The MR head cannot write, and therefore actually is combined with a write inductive head as an MR-inductive composite head (hereinafter referred to as the magnetic head or MR/IND head).

The magnetic head, as shown in Fig. 5, may come into contact with a medium directly or indirectly through dusts due to a protrusion or dust on the disc.

At the contact point, frictional heating causes a sharp temperature rise. In the case where the contact point is in the vicinity of the MR element, the resistance of the MR element is known to change with temperature, thereby causing an output fluctuation. This output fluctuation is called a thermal asperity. An example of thermal asperity is shown in Fig. 7. In this way, the thermal asperity 72 is observed in a form added to a data signal 71.

Conventional techniques for removing the thermal asperity are disclosed in JP-A-2-154310 and JP-A-2-54403. The former is a method in which two MR elements are configured differentially to cancel the thermal asperity by differential detection.

In the latter method, a positive envelope 73 and a negative envelope 74 shown in Fig. 7 are detected from a detection signal superimposed with a thermal asperity, which is detected from these envelopes. The thermal asperity thus obtained is used to separate a thermal asperity from the signal containing it.

The former method has the problem that a track width corresponding to two MR elements is required and therefore it is structurally difficult to narrow the track width.

The latter method, on the other hand, though free of the restraint of narrowing the track width, is liable to pose the problem that signal processing requires a considerable time, and therefore it is difficult to read the address signal of a track and decide within a predetermined time whether the address thus read is that to be accessed. For this reason, a possible solution would be that the circuit for removing the thermal asperity is prevented from turning on normally but upon detection of a data error as a probable cause of the thermal asperity after one rotation of the medium thereby to remove the noise. Such a method, however, makes real-time processing impossible, thus deteriorating the data throughput. Also, in the case where the thermal asperity undergoes a sharp change or the frequency of the thermal asperity is near the signal frequency, a correct envelope cannot be obtained. As a result, the input signal cannot be completely corrected, often resulting in a data error.

The object of the present invention is to provide an MR head and a magnetic disc apparatus in which the thermal asperity isretvedinr-tiii without restricting the track width.

According to the invention, there is provided a magnetoresistive head comprising a magnetoresistive element for detecting magnetism utilizing the magnetoresistive effect, a temperature detector disposed in the vicinity of the magnetoresistive element for detecting the information relating to the temperature change of the magnetoresistive element and means for outputting the detected temperature change information as an output.

In view of the fact that the temperature detector is arranged in the vicinity of the magnetoresistive element, the temperature of the temperature detector is substantially equal to that of the magnetoresistive element. The temperature detector changes in resistance in accordance with the temperature, and this resistance change is proportional to that due to the temperature change of the magnetoresistive element. As a consequence, after appropriately amplifying the output from the temperature detector and the output from the magnetoresistive element, the difference between the two outputs is taken. In this way, a temperature compensation is accomplished to remove the effect of the temperature change from the output of the magnetoresistive element.

Th the drawis Fig. 1 is a circuit diagram for explaining a method of temperature compensation of an MR head according to this invention; Fig. 2 is a diagram showing the configuration of an MR head according to an embodiment of the invention; Fig. 3 is a diagram showing the configuration of an MR head according to another embodiment of the invention; Fig. 4 is a diagram showing the configuration of an MR head according to still another embodiment of the invention; Fig. 5 is a diagram for explaining the manner in which a magnetic head is in contact with a disc; Fig. 6 shows the configuration of a disc apparatus; and Fig. 7 is a diagram for explaining the reproduction signal obtained when a thermal asperity is generated.

An embodiment of the invention will be explained below with reference to Figs. 1 and 2.

Fig. 2 shows an example configuration of a magnetic head according to the invention. For simplicity, only a part including magnetoresistive element relating to the invention is shown. This diagram does not show a recording head nor an upper shield for preventing the MR element 7 from detecting the magnetic field from a bit other than the one that the MR element 7 intends to read, etc.

The magnetic head includes a separation layer 2, a lower shield layer 3 and a separation layer 4 formed on a slider member 1 for mounting the magnetic head, and a bias layer 5 thereon, and an MR layer (MR element) 7 through a separation layer 6 of an insulating or high resistance material. The separation layer 2 is for improving the adhesiveness between the slider member 1 and the lower shield layer 3. The lower shield layer 3 and the upper shield (not shown) are for preventing the MR element 7 from detecting the magnetic field from a bit other than the one which the MR element 7 intends to read. The separation layer 4 separates the lower shield layer 3 magnetically from the bias layer 5. The bias layer 5 is for applying a bias magnetic field in a predetermined direction to the MR element. This magnetic field applied to the MR element 7 is generated by supplying current to the bias layer 5. The bias magnetic field has the function of optimizing the sensitivity of the MR element 7. The separation layer 6 is for separating the bias layer 5 and the MR element 7 electrically from each other and facilitating the control of the current flowing therein. The MR element 7 carries thereon a magnetic domain control layer 8 for reducing the Barkhausen noise, a layer 9 for restricting the track width from the viewpoint of manufacture, and electrodes 10A, lOB arranged at the ends of the MR layer 7. The electrode lOB is connected to the MR layer 7 through the magnetic domain control layer 8 working as a conductor.

According to this embodiment, the bias layer 5 is utilized as a layer for detecting the temperature change of the MR head. The separation layer 6 interposed between the MR layer 7 and the bias layer 5 is about 5 to 50 nm thick, and the MR layer 7 is considered substantially the same in temperature as the bias layer 5. In order to supply current to the MR layer 7 and the bias layer 5 separately, electrodes are provided at the ends of the bias layer 5. One electrode shares a lead wire with the electrode 10A of the MR layer 7 in order to reduce the number of lead wires. Supplying current separately to the bias layer 5 and the MR layer 7 leads to the advantage of facilitating the control of bias current.

In this configuration, the bias layer 5, the MR layer 7, the magnetic domain control layer 8 and the electrode 10 are made of a conductive material. The separation layer 6, which is preferably made of an insulating material, may be of a high-resistance metal.

Also, the separation layer 6 may be done without. The bias layer 5 may be either a shunt bias for generating a magnetic field by supplying current to a conductor or a soft adjacent layer (SAL) in which current is supplied to a soft magnetic material. In either case, the bias layer 5 can be used as a temperature-detection layer.

Now, explanation will be made about an example configuration of the circuit for removing the thermal asperity with reference to Fig. 1. In Fig. 1, the MR head 30 is represented by an equivalent circuit, and the same component parts as those in Fig. 2 are denoted by the same reference numerals as in Fig. 2 respectively.

In Fig. 1, the circuit is driven by a constant current. The MR layer 7 detects a magnetic signal and the thermal asperity, and the bias layer 5 a change due to the thermal asperity but not a magnetic signal. When a constant current is supplied to the MR layer 7 and the bias layer 5, voltages corresponding to the resistance changes are observed across the MR layer 7 and the bias layer 5, respectively. The AC components of these voltages are amplified at differential amplifiers 20 and 20', respectively. Then, in order to correct the difference in current and resistance change rate with respect to the temperature between the bias layer 5 and the MR layer 7, they are regulated using the amplifier 21, and inputted to the differential amplifier 22. At the amplifier 22, the signal from the MR layer 7 and the signal from the bias layer 5 are differentially amplified to remove the thermal asperity, while preventing the magnetic signal detected by the MR layer 7 from unnecessary changing.

Apart from the constant-current drive method described above, the current can alternatively be differentially amplified by the use of the constantvoltage drive method.

The temperature-detection layer can be mounted on the MR head of any type which can be configured in various ways. Another embodiment of the invention is explained with reference to Figs. 3 and 4.

Figs. 3 and 4 are views of the magnetic head taken from the side of the magnetic head in contact with the disc. Fig. 3 shows the temperature-detection layer 12 arranged separately from the bias layer 5, with the temperature-detection layer 12 arranged under the separation layer 11 of a conventional type MR head. An electrode lOC is dedicated for the temperature detection layer 12, and the electrode lOA on the opposite side is shared by the MR element 7 and the bias layer 5.

Fig. 4 shows an example of the MR head including a temperature detection layer 12, in addition to the elements of the conventional MR head, such as a separation layer 23 and a spacer layer 13, a magnetic domain control layer 8 made of an insulating material. As in the case of Fig. 3, the MR head includes an electrode lOC dedicated for the temperature detection layer 12 and the electrode 10A shared with the MR element 7.

As described above, the main point of the invention is to provide a temperature-detection layer in the vicinity of an MR layer, and embodiments thereof are not limited in any way by the head configuration, arrangement, materials, processes, etc.

Now, the general configuration of a magnetic disc apparatus comprising an MR head and a thermal asperity compensation circuit according to the invention are shown in Fig. 6. The thermal asperity compensation circuit described with reference to Fig. 1 is incorporated in an R/W preamplifier/thermal asperity compensation amplifier 63. The operation of the magnetic disc apparatus will be briefly explained. An MR/IND head is driven along the disc surface by a voice coil motor (VCM) 62 to write data into and read data from a target position on the magnetic disc 68. For data read operation, the thermal asperity is removed by an R/W preamplifier/thermal asperity compensation amplifier 63 from the reproduction output of the MR/IND head 61. In the case where the reproduced signal after the thermal asperity removal corresponds to the signal on the data region of the magnetic disc 68, the signal is applied to an R/W channel & discriminator circuit 64. In the case where the signal corresponds to the signal on the servo signal region of the magnetic disc 68, it is supplied to a position signal demodulator 65, so that a head position controller 66 performs such operations as seeking or track following of the MR/IND head 61 on the basis of the signal.

In this magnetic disc apparatus, the thermal asperity is removed from the signal outputted from the MR head. It is therefore possible to prevent an misoperation of position control and data error due to the thermal asperity.

It will thus be understood from the foregoing description that according to the invention, the thermal asperity superimposed on a data signal is removed real-timely using an output from temperature detection means, and therefore the data throughput is improved.

Also, even when a sharp thermal asperity occurs, the data is properly compensated for an improved data reliability.

Further, although discs of inferior flatness contact the MR head more frequently and are treated as defective items due to the resulting thermal asperity, the method of cancelling the thermal asperity and the MR head according to the invention permit the use of even those discs which have thus far been categorized as defective items.

Claims (9)

1. A magnetoresistive head having a magnetoresistive element for detecting magnetic field by the use of the magnetoresistive effect, comprising: temperature detection means for detecting the temperature change of the magnetoresistive element; and means for outputting information on the temperature change detected by said temperature detection means.

2. A magnetoresistive head according to Claim 1, wherein: said temperature detection means is made of a material having a resistance changing with temperature, and said output means outputs information on the resistance change of the temperature detection means as a signal of the same type as the output of the magnetoresistive element.

3. A magnetoresistive head according to Claim 1, wherein: said temperature detection means also works as a bias layer for applying a bias magnetic field to the magnetoresistive element, and said output means supplies a current to the bias layer.

4. A magnetoresistive head according to Claim 2, wherein: said magnetoresistive element and said temperature detection means are electrically insulated electrically from each other.

5. A magnetic disc apparatus comprising: a magnetoresistive head including means for detecting the temperature change of a magnetoresistive element and means for outputting information on the temperature change; and means for removing the thermal asperity from the output signal of the magnetoresistive element on the basis of the information on the temperature change.

6. A magnetic disc apparatus according to Claim 5, wherein: said temperature detection means for the magnetoresistiye head is made of a material changing in resistance with temperature, and said output means outputs a signal of the same type as the output signal of the magnetoresistive element; and said means for removing thermal asperity compensates the resistance change rates with respect to temperature of the temperature detection means and the magnetoresistive element and the output signal levels of the temperature detection means and the magnetoresistive element, and cancels the thermal asperity by taking the difference between the two compensated signals.

7. A method for removing the thermal asperity from the output of a magnetoresistive head, comprising the steps of: detecting the temperature change of a magnetoresistive element of the magnetoresistive head; obtaining information on the temperature change independently of the output of the magnetoresistive element; and removing the effect of temperature change from the output of the magnetoresistive element by the use of the information on the temperature change.

8. A nagnetoresistive head substantially as herein described with reference to and as illustrated in Figs. 1 and 2, or Fig. 3, or Fig. 4 of the accompanying drawings.

9. A method for removing the thermal asperity from the output of a magnetic head substantially as any one herein described with reference to the accompanying drawings.