JPH01119903A - Superconducting multi-level recording method - Google Patents

Abstract

PURPOSE:To attain multi-level recording in terms of magnetic flux quanta and to obtain a large capacity of a storage device by altering the size and direction of a current which is caused to flow in a head at a temperature below the critical temperature of a superconducting thin film recording medium. CONSTITUTION:By using a second superconducting thin film recording medium 4 having a multiple pinning centers of the magnetic flux quanta 9, and the recording head which complementarily impresses the magnetic field of the reversed polarity on the recording medium 4, the current is caused to flow in the head at the temperature below the critical temperature of the superconducting thin film recording medium 4. Apart from a storage state in which a magnetization direction, a shape and a change are set to correspond to one information bit such as conventional magnetic storage and optical stor age, the number and direction of the magnetic flux quanta 9 pinned by lattice fault, etc., can be controlled by altering the size and direction of the current which is caused to flow in the head. Thus, information can be recorded in a multi-level, and a large capacity of the storage device can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording method for a storage device using a superconducting thin film as a recording medium.

[Prior Art] Conventionally, memory elements utilizing superconducting phenomena, as typified by Josephson memory, have required complex wiring and processes such as multiple read lines, write lines, and Josephson junctions. Therefore, high-speed recording and reproducing operations are possible, but it is not suitable for large-capacity storage devices.

In addition, in the perpendicular magnetic recording method, which is theoretically capable of high-density recording, a hard magnetic film with an easy axis of magnetization perpendicular to the film surface is saturated in the perpendicular direction of the film, and antiparallel magnetization is Since information is stored in the joint, it is basically a binary record.

[Problems to be Solved by the Invention] An object of the present invention is to provide a recording method using a second type of superconducting thin film medium for realizing a large-capacity storage device.

[Means for Solving the Problems] The present invention uses a second type of superconducting thin film recording medium having a large number of magnetic flux quantum pinning centers, and a recording head that applies a magnetic field of opposite polarity complementary to the recording medium, It is characterized by controlling the number and direction of magnetic flux quanta pinned onto the recording medium by changing the magnitude and direction of the current flowing through the head below the critical temperature of the superconducting thin film recording medium.

[Function] The present invention, unlike conventional magnetic storage and optical storage,
This is completely different from the storage format in which shape or phase change corresponds to a single information bit, and by controlling the number and direction of magnetic flux quanta pinned to lattice defects etc. by changing the magnitude and direction of the current flowing through the head. , it is possible to record information at a multilevel level.

[Example] Fig. 1 is a diagram for explaining the present invention in detail, in which 1 is a floating Rad slider, 2 is a head winding, 3 is a Rad core, and 4 is a large number of gratings having a pinning effect of magnetic flux quantum. defect·
A disk-shaped type 2 superconducting Fi'Jm recording medium having an irregular pinning center, 5 is a substrate, and 6 and 7 are recording tracks. Reference numeral 8 designates an inlet for cooling gas or cooling liquid for cooling the medium 4 below its critical temperature T.

Currently, Y-Ba-Cu-0 based oxide superconductors have a critical temperature Tc of around 90°C, and it is sufficient to use liquid nitrogen (boiling point 77K) for cooling. If Tc is above room temperature, such a cooling mechanism is not necessary. In the recording method according to the present invention, either the recording medium or the head is rotated to perform multi-level recording on concentric tracks. The principle of multilevel recording using this method will be briefly explained below.

Figure 2 shows the 2nd f! ! ! This figure shows the relationship between the magnitude of the magnetic field and the amount of magnetic flux φ penetrating into the thin film when a magnetic field (Ha) is applied in a direction perpendicular to the film surface of the superconducting thin film. lla
When increasing from O, the magnetic flux penetrating the thin film becomes ■→
It changes like ■−■−■−■.

That is, up to the lower critical magnetic field HCI, the magnetic flux is completely eliminated by the Meissner effect, but when it exceeds OCt, the magnetic flux begins to invade, and at the upper critical magnetic field HC2, it becomes equal to the external magnetic field and transitions to a normally conducting state.

The penetration of magnetic flux in the region Hcl < Ha < Hc2 is φ0
This occurs in the form of magnetic flux quanta with a magnetic flux of -2・10-'(Gcm"). As Ha increases, the number of magnetic flux quanta increases, and near HC2 the distance between the invading magnetic flux quanta increases due to the material-specific Coherent length ξ(Y-Ba-Cu-0
In oxide superconductors, the number of magnetic flux quanta is approximately 10, and a large number of magnetic flux quanta penetrate. In an ideal superconducting thin film without lattice defects, such penetration of magnetic flux is reversible, and as the applied magnetic field is reduced, the magnetic flux is completely eliminated below HcI. However, if there are magnetic centers, the invading magnetic flux is pinned to these, and the magnetic flux quanta are retained in the medium even when the applied magnetic field is removed. The pinning centers are grain boundaries, lattice defects, dislocations, etc., and their number can be increased by making the grain boundaries finer or introducing lattice defects by neutron irradiation or the like.

The number of magnetic flux quanta retained through this process changes depending on the magnitude of the applied magnetic field. For example, in Fig. 2, if the applied magnetic field is increased from 0 to H, and then changed to O, a magnetic flux of φ is maintained through the process of ■-■-〇-■, but if 111 is increased to Ha2, ■−■−■−■
Through the process, the magnetic flux φ2 is maintained. Furthermore, here,
Needless to say, φ1 (i=1, 2) satisfies the relationship φ1-old φo (Ni: integer). Follower 11
．． By changing , multi-level recording in units of magnetic flux quantum becomes possible.

In this method, for example, a horseshoe-shaped recording head 3 as shown in FIG. 1 is used to apply such an externally applied magnetic field (that is, recording magnetic field) to the medium in a complementary manner. FIG. 3 shows the intensity distribution of the 11□ (perpendicular direction to the thin film) component of the recording magnetic field generated from such a head 3, and the X coordinate is taken in the radial direction of the medium. Penetration of magnetic flux occurs in the region of H2≧MCI. Therefore, when recording is performed using such a head magnetic field, as shown in FIG. 4, a number of magnetic flux quanta corresponding to the strength of the recording magnetic field penetrate into the medium. Furthermore, since the polarity of the recording magnetic field is different in tracks 6 and 7, the magnetic flux quanta in both tracks are in opposite directions, and the continuity of the magnetic flux is maintained in the medium. As shown in the figure, there is also a horizontal component HX in the magnetic field generated from the head, but high-temperature superconductors represented by the Y-Ba-Cu-0 system have a horizontal component HX of +1. Since the medium has strong anisotropy, it can be safely assumed that the amount of magnetic flux retained in the medium is determined approximately by the vertical component H2.

FIG. 5 shows the amount of magnetic flux held in each bit cell on a track recorded by this method and an example of its reproduced waveform. In the figure, the y coordinate is in the track direction, and Lb indicates a 1-bit length. Figure (a)
When the signal of the track whose magnetic flux is pinned is reproduced by a magnetic flux change sensitive sensor as shown in figure (b).
When reproducing with a magnetic flux sensitive sensor, the same figure (C) is obtained.
A reproduced waveform as shown in is obtained. The amount of magnetic flux in FIG. 5(a) is the magnetic flux quantum φ. The reproduced waveforms in FIGS. 3(b) and 3(c) are shown normalized by el, which corresponds to the magnitude of magnetic flux change φ1.

Although FIG. 5 shows an example in which the recording level is -3, it is possible to further increase the recording level by setting the magnitude of the recording magnetic field (recording current) more finely.

[Effects of the Invention] As described above, according to the present invention, multi-level recording in units of magnetic flux quanta becomes possible, and a large-capacity storage device can be realized.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of the second type of superconducting thin film recording medium and recording head for realizing this method, and Figure 2 shows the magnetic field strength and magnetic field intensity when an external magnetic field is applied to the second type of superconducting Ntli. Figure 3 shows the relationship between the amount of magnetic flux penetrating the superconducting thin film, Figure 3 shows the magnetic field strength distribution generated from a horseshoe-shaped recording head, and Figure 4 shows the magnetic flux quantum in a 1-bit cell recorded by the method of the present invention. A conceptual diagram for explaining the state. FIG. 5 is a diagram showing the amount of magnetic flux on a track recorded by this method and an example of its reproduced waveform. DESCRIPTION OF SYMBOLS 1... Floating RAD slider, 2... Head winding, 3... Head core, 4... Type 2 superconducting thin film recording medium, 5... Substrate, 6.7... Recording track, 8 ...Cooling port, 9...Magnetic flux quantum, 1O111...1 bit cell. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] Using a second type of superconducting thin film recording medium having a large number of pinning centers for magnetic flux quanta and a recording head that applies a magnetic field of opposite polarity complementary to the recording medium, the A multilevel recording method, characterized in that the number and direction of magnetic flux quanta pinned onto the recording medium are controlled by changing the magnitude and direction of a current flowing through the head.