JPH06103521B2 - Magnetic playback device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an apparatus for reproducing a signal recorded on a magnetic recording medium, and more particularly to detecting a signal magnetic field from the magnetic recording medium as a change in high frequency characteristics of a magnetic material. The present invention relates to a magnetic reproducing device for performing reproduction.

[Technical Background of the Invention and Problems Thereof] For a method of reproducing a magnetic recording signal by utilizing a change in electromagnetic characteristics of a magnetic body due to a magnetic field (signal magnetic field) based on a recording signal from a magnetic recording medium, a magnetic resistance Although the one utilizing the effect is known, the present inventors have found that as a very excellent method for high-density recording / reproduction, the tensor permeability μ ′ and the loss term μ thereof are changed as a change in the high frequency characteristics of the magnetic substance due to the signal magnetic field. We have already proposed a method that utilizes the change of ″. This method uses ferrite, permalloy,
A recorded signal is reproduced by using a magnetic material such as an amorphous alloy and detecting and rectifying a change in the high frequency output voltage due to a change in impedance of a high frequency circuit coupled to the magnetic material.

By the way, generally, μ ′ and μ ″ of a magnetic material at a high frequency cause a change as shown in FIG. 1 due to an external magnetic field. In this figure, μ ′, μ ″ change 11 in a low magnetic field is an unsaturated region of the magnetic material. The low magnetic field loss that occurs and the change 12 of μ ′ and μ ″ in the high magnetic field indicate the ferromagnetic resonance that occurs in the saturation region of the magnetic material. Also, H _S is the saturation magnetic field of the magnetic material (the magnetic field that begins to saturate), H S _R indicates the ferromagnetic resonance magnetic field, respectively.As can be seen from this figure, the change in μ ′ and μ ″ of the magnetic material is significantly larger when the ferromagnetic resonance is used rather than the low magnetic field loss.
Therefore, a slight change in the magnetic field causes a large change in the impedance of the high-frequency circuit, and reproduction with extremely high sensitivity and good SN ratio becomes possible.

However, assuming that the recording wavelength of the signal magnetic field from the magnetic recording medium is λ with respect to the distance d from the medium. , The signal magnetic field based on the short wavelength recording signal becomes extremely small as the distance from the medium increases. In that case, if the magnetic substance is in an unsaturated state and has a high magnetic permeability, it has a great effect of absorbing the signal magnetic field. For example, by inserting the magnetic substance into a part of a magnetic circuit such as a ring head, the influence of the signal magnetic field is reduced. It can be applied to a place far away from the recording medium, and sensitive reproduction is possible even with a short wavelength recording signal. However, in a saturated state or a magnetic material having a low magnetic permeability close to it, it is not possible to suppress the deterioration of the reproduction sensitivity due to the decrease of the signal magnetic field, and in particular, the reproduction sensitivity of the short wavelength recording signal cannot be sufficiently obtained and the frequency characteristic is deteriorated. Cause

[Object of the Invention] An object of the present invention is to make a magnetic substance for detecting a signal magnetic field sensitively change a high frequency characteristic in accordance with the signal magnetic field in a state of high magnetic permeability, so that a short wavelength recording signal is also improved. It is an object of the present invention to provide a magnetic reproducing device capable of reproducing with high sensitivity.

SUMMARY OF THE INVENTION The present invention is characterized in that a ferromagnetic resonance magnetic field of a magnetic material is set in the vicinity of a saturation magnetic field so that the magnetic material is caused to change in high frequency characteristics due to ferromagnetic resonance in an unsaturated region. For example, the magnetic anisotropy is added to the magnetic substance to make it close to a single magnetic domain, and the magnetic rotating mechanism mainly saturates the magnetic substance in the signal magnetic field direction to suppress the low magnetic field loss due to the multi-domain structure. Can be achieved. As a result, the magnetic substance is sensitive to the signal magnetic field in the unsaturated region and has a high linearity, which causes a change in the high frequency characteristic due to the ferromagnetic resonance.

[Effects of the Invention] According to the present invention, it is possible to cause a change in high-frequency characteristics that is sensitive and has good linearity in response to a signal magnetic field in a state where magnetic permeability is high. Therefore, by using this magnetic material as a magnetic circuit such as a ring head or a part thereof, it becomes possible to reproduce a short wavelength recording signal with extremely high sensitivity.

Embodiment of the Invention FIG. 2 shows an embodiment of the present invention. In the figure, 21 is a magnetic recording medium, on which a magnetic gap is placed.
Head magnetic poles 23 having 22 are arranged in close proximity. A part of the head magnetic pole 23 is composed of a thin film magnetic body 24 whose μ ′ and μ ″ change in response to a signal magnetic field. Then, a conductor piece 25 which comes close to or is attached to the thin film magnetic body 24 is connected. The conductor piece 25 is provided and is connected to a high frequency circuit 26. The high frequency circuit 26 includes a high frequency oscillator 27, matching capacitors 28 and 29, a resonance capacitor 30, and the like.

Now, the thin film magnetic material 24 is generated by the signal magnetic field from the magnetic recording medium 21.
If μ ′ and μ ″ of change, the conductor piece 25
Since the impedance change occurs, the high frequency output voltage taken out from the high frequency circuit 26 via the conductor piece 25 changes according to this impedance change. Therefore, this high frequency output voltage is applied to, for example, the diode 31, the resistor 32, and the capacitor.
A signal reproduction output 35 can be obtained by performing detection with the peak detection circuit 34 including 33.

Wherein a change in frequency characteristics due to the signal magnetic field in the thin film magnetic body 24, i.e. be described conditions that the ferromagnetic resonance, generally ferromagnetic resonance magnetic field shown in FIG. 1 in H _R (x
Direction) has the following relationship with the frequency f of the high-frequency magnetic field applied to the yz plane orthogonal to this.

_{= Γ [{H R + (} Ny-Nx) Ms + (H A x-H A y)} {H R + (Nz-Nx) Ms + (H A x-H A z)}] 1/2 ... (1) γ: Gyromagnetic ratio, usually 2.8MHz / Oersted Nx, y, z: Demagnetization factor when the direction of the ferromagnetic resonance magnetic field (external magnetic field) is the x direction Ms: Saturation magnetization H _A x, _A y , _A z: Anisotropy magnetic field when the direction of the ferromagnetic resonance magnetic field is the x direction. In the embodiment of FIG. 2, the recording track length direction is x, the track vertical direction (recording medium vertical direction) is y, When the track width direction is z, the diamagnetic field coefficient of the thin film magnetic body 24 is z direction, z
Since it is almost 0 in the direction and 1 in the y direction, the ferromagnetic resonance condition of the thin film magnetic body 24 saturated in the x direction is as follows.

f = γ [{H _R + (H _A x −H _A z)} {H _R + Ms + (H _A x −H _A y)}] ^1/2 (2) Then, the high frequency magnetic field in the formula (2) is By appropriately determining the frequency or the anisotropic magnetic fields H _A x, H _A y, H _A z, the ferromagnetic resonance magnetic field H _R can be set near the saturation magnetic field of the thin film magnetic body 24 in the x direction. An example of one setting is shown in FIG.
This figure shows how Co ″ amorphous alloy is used for the thin film magnetic body 24, and how μ ″ actually changes by the external magnetic field H. Ferromagnetic resonance is observed at a place slightly larger than the saturation magnetic field Hs. The magnetic field H _R is set, that is, the bias magnetic field Hb is set at a place smaller than the saturation magnetic field Hs and a sudden change in μ ″ occurs, and the signal magnetic field is superimposed on this bias magnetic field Hb. As a result, the thin film magnetic body 24 is maintained in an unsaturated and large magnetic permeability state, in other words, a state in which the magnetic resistance is low as a part of the head magnetic pole 23, and a sufficiently large change of μ ″ is caused in the thin film magnetic body 24. be able to.

Furthermore, by adding an in-plane-axis magnetic anisotropy having an easy axis of magnetization in the direction orthogonal to the signal magnetic field to the thin film magnetic body 24 (the anisotropic magnetic field generated thereby is referred to as H _K ).
It is possible to reduce the value of μ ″ at the magnetic field 0 in the figure, and thus to make the change of μ ″ sensitive to the signal magnetic field.

FIG. 4 shows that an anisotropic magnetic field H _K is applied to the thin film magnetic body 24 in FIG. 2 in the z direction, a signal magnetic field Hsig is applied in the x direction, and a high frequency magnetic field H _RF is applied to the conductor in FIG. Piece 25
3 shows the change of the magnetic moment M with respect to Hsig when applied in the y direction. Figure 4 (a) shows Hs
ig = 0, indicating the magnetic moment M of the thin film magnetic body 24
Are kept in the direction of the anisotropic magnetic field H _K. Signal magnetic field in this state
When Hsig is applied, the magnetic moment M rotates in the direction of Hsig of the signal magnetic field, as shown in FIG. 4 (b). Further, when the signal magnetic field Hsig exceeds the anisotropy field H _K, Figure 4 magnetic moment M, as shown in (c) is a thin film magnetic 24 is fixed to the x direction is saturated. Hsig = 0 in FIG. 4 (a)
In the state, the ferromagnetic resonance does not occur because the directions of the high frequency magnetic field H _RF and the magnetic moment M are parallel. Therefore, by setting the ferromagnetic resonance magnetic field H _R near the anisotropic magnetic field H _K ,
Signal magnetic field Hsig is added and magnetic moment M becomes signal magnetic field Hsig
It is possible to cause abrupt changes in μ ′ and μ ″ with rotation in the direction.

FIG. 5 shows how μ ″ changes with respect to the external magnetic field H of the permalloy thin film having the above magnetic anisotropy.
Anisotropic magnetic field H _K is approximately 3 [Oe] and external resonance magnetic field is 4.5 [Oe]
e]. The frequency of the high frequency magnetic field H _RF is 350 MHz.
The ferromagnetic resonance magnetic field H _R can be set to a value smaller than the saturation magnetic field H _S, that is, the anisotropic magnetic field H _K.

An embodiment of the present invention is shown in FIG. This is a case where the present invention is applied to the reproduction of a perpendicularly magnetically recorded signal.The magnetic recording medium 61 has a perpendicular magnetic recording layer 62 such as Co--Cr, a high magnetic permeability such as permalloy, and a change in high frequency characteristics due to a signal magnetic field. And a magnetic layer 63 and a base layer 64. 65
Is a main magnetic pole and 66 is a sub magnetic pole, and these are also used as a perpendicular magnetic recording head. The main magnetic pole 65 has a coil 67 connected to the high frequency circuit 26 as shown in FIG.
Is wound. In this case, the magnetic flux generated by the recording magnetic moment of the magnetic recording layer 62 immediately below the main magnetic pole 65 forms a magnetic circuit passing through the main magnetic pole 65, the magnetic layer 63 and the auxiliary magnetic pole 66. In addition, the main magnetic pole 65 and the magnetic layer whose high-frequency characteristics change
63, in some cases the ferromagnetic resonance magnetic field H _R in some sub pole 66 is set in the saturation magnetic field near. Therefore, similarly to the case of FIG. 2, it is possible to cause the main magnetic pole 65, the magnetic layer 62, and in some cases, the auxiliary magnetic pole 66 to change the high frequency characteristics sensitive to the signal magnetic field without lowering the magnetic permeability of the magnetic circuit. You can

FIG. 7 shows another embodiment in which the present invention is applied to the reproduction of a perpendicular magnetic recording signal. Reference numeral 71 is a thin film magnetic body corresponding to the main magnetic pole 65 of FIG. Is a magnetic yoke for forming the magnetic circuit indicated by the arrow. A conductor layer 73 is attached to the thin film magnetic body 71, and the conductor layer 73 is connected to the high frequency circuit 26 of FIG. The ferromagnetic resonance magnetic field H _R of the magnetic body 71 is set near the saturation magnetic field. With this embodiment, the same effect as that of the embodiment shown in FIG. 6 can be obtained.

[Brief description of drawings]

Figure 1 shows the tensor permeability μ'of a magnetic material against an external magnetic field.
And FIG. 2 is a diagram showing a change in loss μ ″, FIG. 2 is a diagram showing a configuration of a magnetic reproducing apparatus according to an embodiment of the present invention, and FIG. 3 is μ ″ with respect to the magnitude of an external magnetic field of a Co type amorphous alloy. FIG. 4 is a diagram showing a change in the magnetic moment of the magnetic substance when an anisotropic magnetic field is applied to the magnetic substance so as to be orthogonal to the signal magnetic field and parallel to the high frequency magnetic field, and FIG. FIGS. 6 and 7 show the change of μ ″ with respect to the magnitude of the external magnetic field of the Ni—Fe alloy to which an anisotropic magnetic field is applied as shown in FIG. 4, FIGS. 6 and 7 for reproducing the perpendicular magnetic recording signal. It is a figure which shows the applied example: 21 ... magnetic recording medium, 22 ... magnetic gap, 23 ... head magnetic pole, 24 ... magnetic body, 25 ... conductor piece, 26 ... high-frequency circuit, 34 ... Detection circuit, 35 ... Signal reproduction output, 61 ... Magnetic recording medium, 62 ... Perpendicular magnetic recording layer, 63 ... Magnetic material, 65 ...
… Main magnetic pole, 66 …… Sub magnetic pole, 71 …… Thin film magnetic material, 72 …… Magnetic material yoke, 73 …… Conductor layer.

Claims (3)

[Claims] 1. A magnetic recording medium, which detects a change in a high-frequency signal output of a high-frequency circuit coupled to a magnetic body according to a change in a high-frequency characteristic of the magnetic body according to a signal magnetic field from the magnetic recording medium. In a device for reproducing a recorded signal, the ferromagnetic resonance magnetic field of the magnetic material is set near a saturation magnetic field,
A magnetic reproducing apparatus characterized in that a change in high-frequency characteristics due to ferromagnetic resonance is caused to occur in the unsaturated region of the magnetic body. 2. A magnetic reproducing apparatus according to claim 1, wherein the ferromagnetic resonance magnetic field is set in the vicinity of a saturation magnetic field by adding magnetic anisotropy to the magnetic material. . 3. A magnetic reproducing apparatus according to claim 2, wherein the direction of the easy axis of magnetic anisotropy is substantially orthogonal to the direction of the signal magnetic field from the magnetic recording medium.