JPS6360326B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in magnetic scales, particularly magnetic heads suitable for reading signals from high-density magnetic scales.

It is well known that an anisotropic magnetoresistive element made of a ferromagnetic metal thin film has a function of detecting changes in the direction of a magnetic field. In addition, the above-mentioned anisotropic magnetoresistive element can be used as a reading means (magnetic head) for a magnetic scale having magnetic graduations (magnetic gratings) of a predetermined pitch. It has already been proposed to arrange and form magnetic lattices (for example, Japanese Patent Publication No. 57-5067, Utility Model Publication No. 50-50).
(See No. 133117, etc.)

The above-mentioned anisotropic magnetoresistive element requires a saturation magnetic field of 150 Oersted or more in order to avoid the influence of magnetic hysteresis, but when the element is used as a reading head for a magnetic scale, the above-mentioned Since the saturation magnetic field must be obtained from the leakage magnetic field of the magnetic scale, the magnetic scale must have a magnetic graduation pitch of about 1 mm or more, taking into consideration the dimensions of the components of the magnetic head. For example, if a magnetic head is formed with a magnetic scale pitch of 2 mm, a favorable magnetic scale signal can be detected, but in order to increase the output change (resistance change rate) of the magnetic head, In order to provide a direction discrimination function for the relative displacement of the head, the dimensions of the magnetic head are 50 mm.
However, since it is necessary to interpolate the detection signal by the magnetic head, it is inevitable that it will be expensive and have a complicated configuration.

The present invention was made in view of such circumstances,
Embodiments will be described below with reference to embodiments shown in the drawings.

In the embodiment shown in FIG. 1, 1 is a magnetic scale, and a magnetic grating 4 with a predetermined pitch λ is recorded on a magnetic thin film 3 formed on a substrate 2 made of a non-magnetic material.
has. Reference numeral 5 denotes an anisotropic magnetoresistive element made of a ferromagnetic metal thin film, which is movably held on the magnetic scale 1 with a certain clearance Δ. The reason why conventional magnetic heads consisting of anisotropic magnetoresistive elements made of ferromagnetic metal thin films could not detect magnetic scale signal magnetic fields of short wavelengths (short magnetic lattice pitches) is because the magnetic lattice elements are used as units of the elements of the above-mentioned elements. Moreover, since the element plane was arranged perpendicular to the magnetic lattice plane and it was made to directly respond to changes in the direction of the magnetic field in that plane, the relative movement between the scale and the head caused The signal magnetic field that is periodically recorded magnetically changes direction within the element plane, and this is because the signal magnetic field in space is weak and cannot be detected with a short magnetic grating pitch.

Therefore, in this embodiment, in order to increase the detection sensitivity of the magnetic scale signal, reduce the pitch of the magnetic grating 4, and reduce the interpolation of the detection signal, the anisotropic magnetoresistive effect element 5 is used as shown in the figure. The current paths 6 forming each component of the magnetic grating 4 are arranged in a zigzag pattern corresponding to each phase of the magnetic grating 4. However, as the pitch of the magnetic grating 4 becomes smaller, the spread of the leakage magnetic field from the magnetic grating is also drastically reduced, making it impossible to saturate the components of the magnetoresistive element 5, and if left as is, the above-mentioned magnetic hysteresis will occur. Therefore, a magnetic path member 7 made of a highly permeable thin film is provided for each current path 6 as shown in the figure, so as to form a closed magnetic path with each magnetic grid. With this configuration, as shown in FIG. 6, the magnetic path member 7 induces leakage magnetic flux from the magnetic grating 4, so that the current path 6 can be placed in a sufficient saturation magnetic field. Thus, a magnetic head is constituted by the magnetoresistive element 5 made of a ferromagnetic metal thin film and the magnetic path member 7 made of a highly permeable thin film.

Next, to briefly explain the operating principle of the embodiment shown in Fig. 2, the anisotropic effect of electrical resistance means that the resistance changes anisotropically depending on the angle formed between the magnetization direction and the current direction. This is a known physical phenomenon. Here, the magnetization direction does not mean the direction of an externally applied magnetic field, but the direction of magnetization within the ferromagnetic body.

Incidentally, for general ferromagnetic alloys, resistance is maximum when the current and magnetization directions are parallel, and minimum when they are orthogonal, and the resistance value ρ(θ) is ρ(θ)= ρ⊥sin ² θ＋ρcos ² θ ...(1) θ: Angle between the direction of magnetization and the current ρ⊥: Resistance when the direction of magnetization and the direction of the current are perpendicular ρ: The angle between the direction of magnetization and the current It is conventionally known that this is expressed by the relationship of resistance when parallel. Also, equation (1) can be rewritten as follows.

ρ (θ) = ρ ₀ −△ρsin ² θ ...(2) ρ ₀ : Resistance value without magnetic field = ρ) △ρ : Amount of resistance change when magnetization is directed in the direction of the difficult axis (= ρ − ρ ⊥) When no external magnetic field is applied to a striped ferromagnetic thin film, or when it is very weak, the spontaneous magnetization in the ferromagnetic thin film is aligned with the axis of easy magnetization (current direction). When a magnetic field is applied in a direction perpendicular to the easy axis direction, the magnetization rotates on the inner surface depending on the strength of the external magnetic field, and the resistance value of the ferromagnetic thin film changes as the magnetization rotates.

In this case, the rotational direction of magnetization due to the external magnetic field H has the relationship sinθ=H/κ ₁ H _S , and the resistance value ρ is ρ ₀ =ρ ₀ −△ρ(H/κ ₁ H _S ) ² ... …(3) is expressed by the external magnetic field H recorded in the periphery.
＝κ ₂ H _S sin θγ (θγ: magnetic field angle with period of magnetic scale pitch), the resistance value of equation (3) is ρ＝ρ ₀ −△ρ・κ ₃ sin ² θγ ……(4 ) κ _i : All constants 0<κ _i <1 H _s : Expressed by the saturation magnetic field of the ferromagnetic thin film.

Now, using the above-mentioned anisotropic magnetoresistive element made of a ferromagnetic thin film, as shown in FIG. , predetermined interval approximately 1/2 (n+1/2)
The current paths are arranged so that they are approximately parallel to each other, separated by λ, and an output terminal is provided at the connection part of the current path (n=
If it is 0, the distance between both elements is λ/4).

The resistance values ρ ₁ and ρ ₂ of the ferromagnetic thin film elements that form the first and second current paths of this element can be made to respond to changes in the strength of the magnetic field or to changes in the direction of the magnetic field. In either case, a periodic magnetic field with a phase angle of 90° is applied, and from the relationship in equation (4) or (5), ρ ₁ = ρ ₀ −△ρsin ² θ ρ ₂ = ρ ₀ −△ρsin ² (90°+θ) ...(6), and the midpoint output △V is △V≒V _B /2-△ρ·V _B cos2θ/4ρ ₀ ...(7).

That is, in either case, the output signal is obtained as a signal with a frequency double the signal magnetic field, and the effect of the anisotropic magnetoresistive element is the same.

Also, from equation (6), there is the relationship ρ ₁ + ρ ₂ = 2ρ ₀ −△ρ ...(8), and the effect that the total resistance value of the above element is always constant regardless of the signal magnetic field is also the same. It is.

First, in the arrangement of the magnetic path members relative to the magnetic grid as shown in FIG. 1, as is clear from FIG. 6, most of the signal magnetic flux φ of the magnetic grid flows back through the magnetic path member. Then, some percentage of the signal magnetic flux φ leaks to adjacent magnetic path members.

This leakage magnetic field H is applied in a direction approximately perpendicular to the current path (that is, the current direction) of the magnetoresistive element,
The spontaneous magnetization of the current path changes the direction of magnetization in the direction of the leakage magnetic field, and the resistance value of the current path changes depending on the magnetization rotation angle.

Regarding FIG. 1, when the magnetic path member is shifted from the magnetic grid by λ/4 (grid pitch: λ),
After the signal magnetic flux φ of the magnetic lattice, the proportion of the magnetic flux flowing back through the magnetic path member decreases, and the proportion of space leakage increases.

Therefore, H is also relatively reduced, the spontaneous magnetization of the current path hardly changes the direction of magnetization, and the resistance value of the current path hardly changes.

In this way, as the magnetic grating and the magnetic path member/current path move relative to each other, the magnetic field applied to the current path has a direction approximately perpendicular to the current direction and a magnitude with a repetition period of λ/2. Therefore, the output of the magnetic head constructed according to the invention varies by twice the period of the magnetic grating.

As is clear from Fig. 1, when using a Ni-C ₀ thin film as an anisotropic magnetoresistive element,
Since the thin film has uniaxial symmetry, the output is repeated twice for each pitch of the magnetic grating 4 (double frequency output).
is obtained.

Further, the ferromagnetic metal thin film forming the anisotropic magnetoresistive element 5 and the highly permeable thin film forming the magnetic path member 7 generally need to be electrically insulated. Therefore, for example, after forming a ferromagnetic thin film such as Ni-C ₀ on a substrate such as glass, glazed ceramic, or silicon, an electrically insulating layer with a low magnetic shielding effect is made of a thin film such as SiO ₂ , and then permalloy etc. A highly permeable thin film is formed. In this case, it goes without saying that the order in which the thin films are stacked on the substrate surface may be reversed to that described above.

Furthermore, the current i flowing through the current path 6 and the magnetic flux φ flowing from the magnetic grid 4 are in the same (or opposite) direction, and only the strength of the magnetic field changes. Therefore, by increasing the detection output voltage by the magnetic head mentioned above,
In order to increase the electromagnetic conversion efficiency, a bias magnetic field is applied by a permanent magnet or the like in a direction substantially perpendicular to the main current direction to give an in-plane magnetic field change to the anisotropic magnetoresistive element. The relationship between the magnetic field H in the magnetic head and the detected output voltage E is shown in FIG. In the same figure, the dotted line represents the hysteresis characteristic, and the upper and lower solid lines represent the characteristics when the main current I and the magnetic field H are parallel and perpendicular to each other, H _r is the reversible magnetic field, H _S is the saturation magnetic field, and H _B is the bias magnetic field. show.

In addition, the current paths of each anisotropic magnetoresistive element forming the magnetic head have the same pattern shape,
Rather than placing them perpendicular to each other,
They are configured to be separated by nλ/2±λ/4, and arranged so that the current directions are the same and the magnetic fields have a phase difference of λ/4 (equivalent to the magnetic fields being orthogonal). In addition, in order to discriminate the detection direction of the magnetic head, that is, the direction of relative displacement between the magnetic head and the magnetic scale, at least two anisotropic magnetoresistive elements are used to obtain two-phase detection outputs.
Assemble and arrange. Considering that this type of anisotropic magnetoresistive element can obtain double frequency detection output, it is preferable that the generally required magnetic lattice phase difference between both elements be nλ/2 + λ/8. be.

Thus, the magnetic head of the present invention, for example as shown in FIG.
Consists of 0. However, in the figure, 11 to 14 are current terminals, and 15 and 16 are output terminals.

In order to strengthen the leakage magnetic field from the magnetic lattice and enhance the magnetic flux guiding effect by the closed magnetic circuit described above, it is more effective to adopt a configuration as shown in FIG. 4, for example. In the same figure, magnetic scale 1
Reference numeral 7 is composed of a magnetic grating 18 subjected to longitudinal magnetic field recording and a substrate 19 made of a highly permeable material. By configuring the magnetic scale in this way, the leakage magnetic field can be strengthened, and on the other hand, the magnetic path member 2 made of a highly permeable thin film for forming the closed magnetic path.
0 enhances the magnetic flux guiding effect by connecting everything behind it.

Next, another embodiment of the present invention is shown in FIG. In the figure, an anisotropic magnetoresistive element 21 is made of a ferromagnetic metal thin film having a relatively high magnetic permeability, such as a thin film such as permalloy. As described above, each magnetoresistive path is electrically coupled with a non-magnetic conductive thin film 25. Note that 26 is a substrate made of a magnetically conductive material. In this embodiment, only the thin film 25 is used in place of the current path, and the structure of the magnetic head can be extremely simplified. In addition, both ends of the magnetoresistive path 6 in FIGS. 1 and 4 are connected to current and output terminals as shown in FIG. 3.

As explained above, according to the present invention, a magnetic head suitable for reading signals on a magnetic scale for high-density recording can be precisely and easily formed, and since the interpolation of detection signals can be reduced, the configuration of the detection circuit can also be improved. Since it can be simplified, it is possible to provide an inexpensive and highly accurate magnetic scale.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing the main parts of an embodiment of the present invention, FIG. 2 is a curve diagram showing the relationship between the magnetic field of the anisotropic magnetoresistive element and the detected output voltage, and FIG. 3 is a diagram according to the present invention. FIG. 4 and FIG. 5 are schematic diagrams showing main parts of other embodiments of the present invention, and FIG. 6 is a schematic front view of the main parts of FIG. 1. It is.

Claims (1)

[Claims] 1. A plurality of current paths forming each component of an anisotropic magnetoresistive element formed by a ferromagnetic thin film having an anisotropic magnetoresistive effect are connected to each phase of a magnetic grating of a magnetic scale. Two sets of components are arranged corresponding to each other and have the respective current paths connected in series, and are separated by a predetermined distance, and an output terminal is provided at the connection part of the elements, and each of the other components is A magnetic head characterized in that it is configured with a current supply terminal provided at the end. 2. For each current path, a magnetic path member made of a highly permeable thin film is arranged with an electrically insulating layer interposed between the ferromagnetic magnetoresistive thin film forming the current path, and the magnetic path member 2. The magnetic head according to claim 1, wherein magnetic flux is guided from the magnetic grid to the current path. 3. The magnetic head according to claim 1, wherein each of the current paths is formed independently, and a nonmagnetic conductive thin film electrically connects each of the independent current paths. 4. Claims 1 to 3, characterized in that a bias magnetic field is applied in a direction substantially perpendicular to the current path to provide a magnetic field change within the plane of the anisotropic magnetoresistive element. Magnetic head as described in section.