JPS6248882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for magnetizing a permanent magnet that requires magnetization accuracy and stability.

Permanent magnets magnetized to an appropriate strength are used as bias magnetic field supply means for magnetic bubble chips and magnetoresistive elements. For example, a magnetic bubble chip requires an appropriate bias magnetic field for its normal storage operation, and if the bias magnetic field is not set to a predetermined value, the storage operation margin of the magnetic bubble chip will be narrowed.

Furthermore, in order to read information recorded on a magnetic recording medium by identifying its polarity using a magnetoresistive element, it is necessary to apply a bias magnetic field to the magnetoresistive element. It is desirable to set the strength of the bias magnetic field to such a strength that the direction of magnetization within the magnetoresistive element is tilted at exactly 45 degrees from the easy axis direction, and as it deviates from this direction, the symmetry with respect to the input signal increases. The range in which good output waveforms can be obtained becomes narrower.

When a permanent magnet is used as a bias magnetic field applying means in this way, it is required not only to have precision in its magnetization strength but also to be stable against external magnetic fields.

Conventional magnetizing devices of this type are used to magnetize magnetic bubble modules, and after a permanent magnet housed in a magnetic shield case is once saturated and magnetized under a DC electromagnet, the electromagnet is supplied. There is a known structure in which the direction of the current is reversed to demagnetize the permanent magnet, the bias magnetic field in the module is set to a specified value, and then an alternating magnetic field is applied to stabilize the magnetization of the permanent magnet. It is being This is described, for example, in IEEE Transactions on Magnetics, Vol. 12, No. 6, pp. 645-647, published November 1976.

However, when magnetizing a magnetic bubble module using such a device, the magnetic field required for saturation magnetization is almost
The _{demagnetizing} magnetic field is approximately several KO _e , whereas the alternating magnetic field is only a few hundred O _e at most. Therefore, the magnetic bubble module is not only weak against external disturbance magnetic fields, but also weak against the desired bias magnetic field. Since the set value caused by the demagnetizing magnetic field deviates due to the application of the alternating magnetic field, the setting accuracy was poor.

The magnetizing device according to the present invention is characterized in that it enables demagnetization using an alternating magnetic field after saturation magnetization, and its first purpose is to achieve high setting accuracy when setting a bias magnetic field in a magnetic bubble module, etc. The object of the present invention is to provide a magnetizing device that can be obtained. A second object is to provide a magnetizing device capable of magnetizing the module in a manner that enhances its stability against external disturbing magnetic fields.

The invention will be explained in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the magnetizing device of the present invention, in which 10 is a DC power supply with variable voltage value, 20, 30, 40
is a switch, 31 is a diode, 50 is a capacitor, 60 is an exciting coil, 70 is a magnetizing yoke, 80
is a magnetic bubble module, and the circuit on the left side from switch 40 constitutes an exciter. To operate this, first, as shown in FIG. 2A, the switch 20 is closed and the capacitor 50 is charged approximately equal to the voltage value of the DC power supply 10. Next, the switch 20 is opened and the switch 40 is closed to cause the excitation coil 60 to discharge the charge in the capacitor 50. At this time, the waveform of the current flowing through the excitation coil 60 is switched between two ways by opening and closing a switch 0 connected to the diode 31.

That is, when the switch 30 is closed, two parallel circuits, ie, a series circuit of the excitation coil 60 and the diode 31 and the switch 30, are connected to the capacitor 50 as shown in FIG. 2B. Therefore, when the charge in the capacitor 50 is first discharged, a current flows in the exciting coil in the direction of the arrow 90. As a result, charge of the opposite polarity is accumulated in the capacitor 50. This charge is transferred to switch 30 and diode 3.
1 and is discharged through a resistive load consisting of arrow 9
Current flows in one direction. In this way, only a unipolar current flows through the excitation coil 60, and a unipolar magnetic field 1 for saturation magnetization flows through the magnetic bubble module 80.
00 is supplied.

On the other hand, when the switch 30 is open,
As shown in FIG. 2, an LC parallel resonant circuit consisting of a capacitor 50 and an excitation coil 60 is constructed, and the charge stored in the capacitor 50 reciprocates within the resonant circuit. As a result, an attenuated alternating current flows through the excitation coil 60, and a demagnetizing attenuating alternating magnetic field 101 can be generated in the magnetic bubble module 80 via the magnetic yoke 70. Excitation coil 60 generated in this way
The amplitude of the current flowing through the capacitor 50 can be arbitrarily selected by changing the voltage value of the DC power supply 10 and changing the charging voltage to the capacitor 50.

FIG. 3 shows a current pattern to the excitation coil necessary for magnetizing the magnetic bubble module in the magnetizing device shown in FIG. 2. FIG. A unipolar excitation coil current 300 is provided in the operation shown in FIGS. 2A and 2B, and its amplitude is I _MAG . This applies a magnetic field with an amplitude of 10 KO _e or more to the magnetic bubble module, completely magnetizing the permanent magnets in the module to saturation in one direction. Next, by carrying out the operations shown in _FIG . The permanent magnet in the Yule is demagnetized from its saturated state. This value of I _DEM generates a demagnetizing magnetic field of several KO _e in the magnetizing yoke. The amplitudes of current I _MAG and I _DEM to the excitation coil can be set by changing the voltage value of the DC power supply 10.

FIG. 4 shows the characteristics of this demagnetizing operation. The bias magnetic field H _B generated in the magnetic bubble module shows a value corresponding to the zero point immediately after saturation magnetization, but it can be set accurately to H _B1 by applying a damping cross current of the second peak value I _DEM1 . Show what you can do. The relationship between H _B and _IDEM is almost linear,
Bias magnetic field establishment accuracy of 0.5 Oe or less can be easily obtained. Moreover, the fact that a bias magnetic field can be established by demagnetizing once in an attenuated alternating magnetic field after saturation magnetization is an unprecedented advantage. Furthermore, according to this demagnetization operation, the bias magnetic field value H set in I _DEM1
The advantage of _B1 is that it does not change in any way even if it is disturbed by an external magnetic field smaller than the magnetic field corresponding to _IDEM1 , and the magnetic bubble module can now tolerate a disturbance magnetic field of several KO _e .

Although the case of magnetizing a magnetic bubble module has been specifically explained above, the object to be magnetized may be a permanent magnet for a magnetoresistive element or any other object.

As described above, according to the magnetizing device of the present invention, it is possible to provide a device that easily solves the problems of conventional devices, such as poor magnetization setting accuracy and weakness against interfering magnetic fields.

Note that the circuit configuration of the device shown in the embodiment is merely an example, and a semiconductor may be used as the switch, or a plurality of switches may be used as the power supply.
It may be modified such that it is switched depending on the polarity of the excitation coil current, or alternatively, the alternating excitation coil current 3
10 may be transformed into a waveform that excludes the first peak. Furthermore, although circuit elements such as resistors and parasitic circuit elements may be inserted into each current circuit in FIG. 1, they are not shown in a simplified manner.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the configuration of the magnetizing device of the present invention, and Fig. 2 is a circuit diagram explaining the operation of the device of the present invention. C indicates a state in which a damped alternating current is passed through the excitation coil. Figure 3 shows the excitation coil current waveform of the magnetizing device of the present invention;
The figure is a diagram showing a demagnetization curve used in the present invention. In addition, in the figure, 10 is a DC power supply, 20,
30, 40 are switches, 31 is a diode, 50
is a capacitor, 60 is an excitation coil, 70 is a magnetizing yoke, 80 is a magnetic bubble module as a magnetized object, 90, 91 is a direction of current, 100, 101
is a magnetic field generated by the magnetization yoke and applied to the magnetic bubble module, and 300 and 310 are excitation coil current waveforms.

Claims (1)

[Claims] 1. A magnetizing yoke with an excitation coil that supplies a uniform magnetic field to a magnetized permanent magnet, a capacitor connected in parallel to the excitation coil of the magnetization yoke via a first switch, and a diode connected in parallel to the capacitor. and a second switch;
A magnetizing device comprising: a DC power source connected in parallel to the capacitor via a third switch.