JPH0298807A - Thin film magnetic head - Google Patents

Abstract

PURPOSE:To increase the output of one channel of the thin film magnetic head by adding outputs of plural quantum interference elements and fetching the result as the output of one channel. CONSTITUTION:Four superconductor rings which each have two Josephson junction parts (a), i.e. four DC driving type superconducting quantum interference elements(SQUID) elements are composed of upper superconductor films 5a-5d and lower superconducting materials 2a and 2b. Those four SQUID elements are provided with electrodes 6a-6c for fetching the detection voltage of signal magnetic flux out by applying bias currents. The four SQUID elements are connected in series through those electrodes 6a-6c and the detection output voltages of the four SQUID elements are put together by addition and fetched as the output voltage of one channel. Consequently, the output voltage which is four times as high as that when one SQUID element is provided for one channel is obtained and the output voltage is nearly of millivolt.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a reproducing thin II! for reproducing magnetically recorded information recorded on a magnetic recording medium. Regarding the ij tin ki head,
In particular, a DC-driven superconducting quantum interference device (hereinafter referred to as 5QUID)
This invention relates to a thin film magnetic head for reproduction that utilizes a thin film magnetic head (referred to as an element).

[Prior Art] In recent years, 6N recording and reproducing devices have been steadily increasing their recording capacity and density, and various developments have been made for this purpose. Thin@magnetic heads are a typical example of such a development. Conventional thin-film magnetic heads are generally of the induction type, and are constructed by forming a magnetic yoke, a coil, an extraction electrode, and the like constituting a magnetic circuit on a substrate as a thin film using a thin-film deposition method and photolithography. According to such a thin film magnetic head, the entire recording/reproducing element can be made extremely small, and the track width of the magnetic gap can be made extremely small, so that high density recording can be achieved.

[Problems to be Solved by the Invention] However, in recent years, there has been an unstoppable demand for higher capacity and higher recording density, and even higher capacity and higher density are desired. On the other hand, in the conventional inductive type thin@magnetic head, the reproduction sensitivity is an obstacle to increasing the recording density. That is, as the recording wavelength becomes shorter as the density of recording increases, even if recording is possible, signal magnetic flux cannot be detected with a sufficient S/N ratio and reproduction cannot be performed.

Therefore, the present applicant previously proposed a reproduction thin film magnetic head using a DC-driven SQUID element in Japanese Patent Application No. 63-25442. Its structure is shown in FIG.

In FIG. 3, reference numeral 1 denotes a magnetic substrate made of a high permeability magnetic material. The end surface of the magnetic substrate 1 on the front left side in the figure is opposed in parallel to a magnetic recording medium (not shown) during reproduction.

A groove 1a is formed along the side edge of the substrate 1 facing the magnetic recording medium, and a lower superconducting material 2 is buried within this groove 1a. A magnetic yoke 4 made of a high magnetic permeability magnetic film that guides signal magnetic flux from the magnetic recording medium is provided above the magnetic yoke 4 through a magnetic gap 3 made of an insulating layer (not shown). The rear end portion of the magnetic yoke 4 is directly joined to the magnetic substrate 1.

Furthermore, an upper superconductor film 5 is provided on the magnetic yoke 4. The upper superconductor film 5 is formed so as to straddle the magnetic yoke 4 via an insulating layer (not shown), and both ends thereof are joined to the lower superconductor material 2. The junction is a Josephson junction a with a thin oxide insulating film interposed therebetween. In this way, the lower superconductor material 2 and the upper superconductor film 5 to 2
A superconductor ring, that is, a DC-driven 5QUID element having two Josephson junctions a is constructed.

Furthermore, electrodes 6,6' are provided on the magnetic substrate 1 for applying a bias current to the SQU ID element and extracting a detection signal of signal 6u from the SQU ID element. The electrode 6.6' consists of a thin film of good conductor, and the other electrode 6 is the upper superconductor II! 5, and the other electrode 6' is connected to the lower superconducting material 2.

Furthermore, a protective plate (not shown) is bonded to the above structure on the magnetic substrate 1 to construct a thin film magnetic head.

Next, the operation of this thin magnetic head will be explained.

During reproduction, the thin-film magnetic head is cooled and made to face a rotationally driven magnetic recording medium (not shown) so that the lower superconductor 2 and upper superconductor 11!5 of the 5QUID element become superconducting. Then, the signal magnetic flux of the magnetically recorded information from the medium is guided into the SQUID element via the magnetic yoke 4.

Here, the magnetic flux φ in the 5QtJID element composed of the lower superconducting material 2 and the upper superconducting film 5 is φ=nφ0 and φ=
The current-voltage characteristics of the 5QUID element at (n+1/2)φ0 are as shown in FIG. Here, φ0 is quantum magnetic flux, and φ. = 2.07x 10-” Wb.

As shown in FIG. 4, the current-voltage characteristics of the 5QUID element continuously change between characteristics A and B according to changes in magnetic flux φ. If a current I larger than twice the critical current value 1o of the Josephson junction a is applied from the electric current 8i6 to the SQU ID element, the signal magnetic flux flowing from the magnetic recording medium into the magnetic yoke 4 will change. can be extracted as a change in voltage between the upper superconductor film 5 and the lower superconductor material 2 of the 5QUID element. The relationship between the magnetic flux and the output voltage in this case is as shown in FIG. 5, and the output voltage (2) changes periodically with a predetermined amplitude vo with the period of the quantum magnetic flux φ0.

In the actual reproduction circuit of the SQU ID element, in order to reduce noise, the AC magnetic flux φ with an appropriate stress IS Y r,
In accordance with this, a method is adopted in which the output voltage for φX=φ and +φrsInωj is phase detected. The signal magnetic flux φ can be detected by counting the number of periodic changes in the output voltage using a counting circuit.

In this way, the detection of the signal 6i1 bundle is performed using the DC-driven SQ.
A thin film magnetic head using a U r D element has a much superior ability to detect signal magnetic flux compared to a conventional ring head, an 8-conductor thin film magnetic head, or an MR head.

However, in a thin film magnetic head using such a DC-driven 5QUID element, although the detection sensitivity of the signal bn flux is excellent, the problem is that the voltage generated from the SQU r D element is extremely small, and the output voltage is extremely small. was there.

Therefore, the problem of the present invention is to develop such a DC-driven SQU.
The object of the present invention is to make it possible to obtain a sufficiently large output voltage in an i-film magnetic head for reproduction using an I-D element.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a magnetic yoke made of a magnetic film that guides signal magnetic flux from a magnetic recording medium on a substrate, and a magnetic yoke that guides the signal magnetic flux flowing through the magnetic yoke. In a thin-film magnetic head for reproduction configured with a DC-driven superconducting quantum interference element made of a superconductor film for detection, a plurality of quantum interference elements are provided for one 61st yoke, and the plurality of quantum interference elements are Quantum interference devices were connected in series, and the outputs of each quantum interference device were combined and extracted as one channel output.

[Function] According to such a configuration, the output of one channel of the thin Indium gas head can be increased by combining, that is, adding, the outputs of a plurality of quantum interference elements and taking out the output of one channel.

[Example] Hereinafter, details of embodiments of the present invention will be described with reference to the drawings.

1 and 2 are a cross-sectional view and a plan view showing the structure of a main part of a thin film magnetic head for reproduction using a DC-driven SQUID element according to an embodiment of the present invention. In both figures, parts common or corresponding to those in FIG. 3 described above are indicated by common reference numerals or symbols with alphabets added to common reference numerals, and explanations of the common parts will be omitted.

As shown in FIGS. 1 and 2, the thin film magnetic head of this embodiment differs from the head shown in FIG. 3 in the following points.

That is, first, on the upper surface of the magnetic substrate 1, two pieces of pla, 1b are formed along the left side in the figure, which faces a magnetic recording medium (not shown), and a lower superconducting material 2a is formed on each of these t'f41a, 1b. , 2b are each buried in a band shape.

Further, four upper superconductor films are provided in parallel so as to straddle the magnetic balks 4, respectively, as shown by reference numerals 5a to 5d. Of these, both ends of each of the upper superconductor films 5a and 5b are connected to one lower superconductor material 2a1. : Joined.

Also, an upper superconductor film 5c.

5d are joined to the other lower superconducting material 2b. Upper superconductor film 58 to 5d and lower superconductor material 2
The junctions a and 2b are each configured as a Josephson junction a. Incidentally, insulating films 7a to 7c are formed between the upper superconductor films 58 to 5d, thereby providing insulation.

With this structure, the upper superconductor films 58 to 5d and the lower superconducting materials 2a and 2b form four superconductor rings each having two Josephson junctions a, that is, four DC-driven SQUIDs. The element is configured.

Three electrodes are provided as shown by reference numerals 6a to 6c for applying a bias current to the four SQU ID elements and extracting a detection voltage of the signal magnetic flux. Electrode 6a is provided on the upper superconductor MSa. The electrode 6b is provided over the upper superconductor film 5b and over the upper superconductor film 5c. Further, the electrode 6c is provided on the upper superconductor film 5d. Electrodes 6a at both ends.

6c is connected to an external reproducing circuit as a terminal for applying a bias current and taking out an output signal. For this purpose, lead wires (not shown) are wire-bonded to the electrodes 6a, 6c, or the electrodes 6a, 6c are extended from the shape shown and routed on the magnetic substrate 1.

The above four 5QUs are connected via such electrodes 6a to 6c.
The ID element is directly connected to 51f. i.e. 4 SQUs
The constituent members of the ID element are 6a, 5
a, 2a, 5b, 6b, 5c.

The members 2b, 5d, and 6c are connected in series in this order.

An electrode 6a is placed under such a structure during playback.

A bias current is applied between 60 and 60, and the bias current flows through each member in the above order. Then, four SQs are generated according to the 61 bundles flowing into the magnetic yoke 4 from a magnetic recording medium (not shown).
A voltage is generated between each of the upper superconductor films 5a to 5d and the lower superconducting materials 2a and 2b of the UID element. In other words, in terms of codes only, between 5a and 2a, between 2a and 5b, 5c,
A voltage is generated between 2b and between 2b and 5a. These four voltages are combined, ie, added, by the above-mentioned series connection and taken out from the electrodes 6a and 6c as the output voltage of one channel of the thin film magnetic head.

According to the thin film magnetic head of this embodiment as described above, the detection output voltages of the four SQU ID elements are synthesized and added to obtain one
Since it is taken out as the output voltage of the channel, an output voltage four times as large as that in the case where only one SQU ID element is provided for each channel as shown in Fig. 3 can be obtained.
Output voltages close to millivolts can be obtained. This is an output voltage value that can be sufficiently amplified by the amplifier of the current magnetic recording/reproducing device.

In addition, as the superconducting material forming the lower superconducting materials 2a, 2b and the upper superconducting films 5a to 5d in the above configuration, La-
Ba-Cu-0 series, Y-Ba-Cu-0,+ ceramics, or those with Sr added, and B1-
5r-Ca-Cu-0 system, Tl-Ba-Ca-Cu-0
system, Th-Ba-Pb-Cu-0 system, Th-Ba-Zr
-Cu-0 series ceramics, or the above ceramics to which rare earth elements are added, etc. are used.

Furthermore, with the above configuration, it goes without saying that the reproducing operation is performed with the head cooled so that the upper superconductor films 5a to 5d and the lower superconducting materials 2a and 2b are in a superconducting state.

Although FIGS. 1 and 2 of the above embodiments only show the configuration of one channel of the thin film magnetic head, it is of course possible to create multiple channels by arranging a plurality of the same configuration on the magnetic substrate 1. . In this case, 1
Since the channel configuration is simple, multi-channeling can be easily achieved.

[Effects of the Invention] As is clear from the above description, according to the present invention, there is a magnetic yoke made of a magnetic film on a substrate that guides signal magnetic flux from a magnetic recording medium, and a signal magnetic flux flowing through the magnetic yoke is detected. In a thin film magnetic head for reproduction configured with a DC-driven superconducting quantum interference element made of a superconductor film, a plurality of the quantum interference elements are provided for one magnetic yoke, and the plurality of quantum interference elements are provided for one magnetic yoke. Since the elements are connected in series and the outputs of each quantum interference element are combined and extracted as one channel output, the reproduction sensitivity is significantly superior and a sufficiently high output voltage can be obtained, making it suitable for short wavelength recording. The excellent effects of being able to perform reproduction with a good S/N ratio and being able to cope with higher density recording can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of the main part of a thin-film magnetic head according to an embodiment of the present invention, FIG. 2 is a plan view showing the structure of the main part of the head, and FIG. FIG. 4 is a perspective view showing the structure of the main parts of a thin-film magnetic head, and FIG.
The figure is a diagram showing the 6fi flux-voltage characteristics of the same 5QLI ID element. 1... 6n substrate 2a, 2b... Lower superconducting material 3... Magnetic gap 4... Magnetic yokes 58-5
d... Upper superconductor film 68-6c... Electrode 78-7c... Insulating film a... Josephson junction

Claims (1)

[Claims] 1) A magnetic yoke made of a magnetic film that guides the signal magnetic flux from the magnetic recording medium and a DC-driven superconducting quantum interference element made of a superconductor film that detects the signal magnetic flux flowing through the magnetic yoke are provided on the substrate. In a thin-film magnetic head for reproduction configured with a magnetic yoke, a plurality of quantum interference elements are provided for one magnetic yoke, and the plurality of quantum interference elements are connected in series to combine the outputs of each quantum interference element into one channel. A thin film magnetic head characterized in that it is configured to take out the output as an output.