Thin film head

Details Thin film head Thin film head

2000-01-07

2001-01-09

Cao, Allen T. (Department: 2754)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

C029S603030

Reexamination Certificate

active

06172858

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film head to be used as a head of a magnetic recording/reproducing apparatus.
2. Description of the Related Art
Recently, as the density of magnetic recording has increased more and more, systems with a high recording density of 500 Mb/inch
2
, as a VTR, and 200 Mb/inch
2
, as an HDD, have been put into practical use. These systems primarily make use of an induction type magnetic head. In recent years, however, a thin film head is beginning to be used in place of the induction type magnetic head not only in systems for reproducing fixed head type tape media but in compact HDDs with a low relative velocity of several meters/sec, since the magnetoresistance effect head has a high S/N ratio.
Recently, it is known that a very large magnetic resistance change, a magnetic resistance change or a maximum of larger than 100%, appears in a multilayered film, the first example is an artificial lattice film which is formed by stacking ferromagnetic films and nonmagnetic films, such as Fe/Cr or Co/Cu, under certain conditions (Phys. Rev. Lett., Vol. 61, 2472 (1988), Phys. Rev. Lett., Vol. 64, 2304 (1990)). It is also reported that the rate of change in magnetic resistance varies periodically when the thickness of the nonmagnetic film is changed. It is explained that this change is brought about since the ferromagnetic film periodically experiences ferromagnetic coupling or antiferromagnetic coupling depending on the thickness of the nonmagnetic film. The electrical resistance of the stacked film is high in an antiferromagnetic coupled state and low in a ferromagnetic coupled state.
The second example is a system in which two types of films with different coercive forces are used, and a magnetic resistance change is realized by setting magnetizations of these two magnetic films in an antiparallel state by using the difference in coercive force (The Journal of The Japan Applied Magnetics society, Vol. 15, No. 5, 813 (1991), a so-called Shinjo type).
The third example is a system in which an exchange bias generated by an antiferromagnetic film is applied to one of two magnetic films sandwiching a nonmagnetic film to thereby Lock magnetization of that magnetic film, and magnetization of the other magnetic film is reversed by an external magnetic field. This realizes a large change in a magnetic resistance by producing states in which the magnetizations of the magnetic films are parallel and antiparallel to each other via the nonmagnetic film (Phys. Rev. B., Vol. 45806 (1992), J. Appl. Phys., Vol. 69, 4774 (1991), a so-called spin valve type).
FIG. 1
shows a conventional magnetoresistance effect element.
This conventional magnetoresistance effect element has a contact region B for connecting a lead
101
on each side of a region A corresponding to a track width. Since a high-permeability soft magnetic film
102
d
which responds to magnetization of a medium exists in this region B, this portion also senses recorded information. For this reason, information from the adjacent track is also mixed upon off-track, and this reduces the S/N ratio and makes the track width obscure. When the recording density is 200 Mb/inch
2
, for example, the track width is 7 &mgr;m, and the track spacing is about 2 &mgr;m. In this case, since the track width is relatively large and the space between track is also large, the contact region B does not exist on the neighboring track if the width of the contact region B is set to about 1 &mgr;m or less. Therefore, a leakage output (crosstalk) from the neighboring track is negligible in off-track with a track spacing of 1 &mgr;m or less.
In
FIG. 1
, numeral
102
a
represents an undercoat film, numeral
102
b
represents a soft magnetic film for applying a bias, numeral
102
c
represents a nonmagnetic film, and numeral
102
e
represents a protective film.
If, however, the recording density is, e.g., 10 Gb/inch
2
, the track width and the track spacing decrease to approximately 1 and 0.2 &mgr;m, respectively, and so the output itself also decreases. This makes the contact region B to exist on the adjacent track upon off-track, and the leakage output from the adjacent track can no longer be neglected. To avoid this inconvenience, the width of the contact region B may be decreased to about 0.2 &mgr;m which is equal to the track spacing. In this case, however, imperfect ohmic contacts readily form in mass production.
The first object of the present invention is as follows.
As described above, as the recording density approaches 10 Gb/inch
2
, the output leaking From the neighboring track through the contact region B upon off-track becomes no longer negligible. If the area of the contact region B is decreased fin order to avoid this leakage output, there arises another problem of the difficulty in forming even ohmic contacts.
In the magnetoresistance effect element, use of a magnetoresistance effect film with a high antiferromagnetic coupled state increases the saturation magnetic field because of a high coupling force of the film. Therefore, there have been reported several systems which use a phenomenon, in which the resistance changes between a parallel magnetization state and an antiparallel magnetization state, rather than the antiferromagnetic coupled state.
The second object of the present invention is as follows.
Another method of precisely defining the track width in a magnetic head is to use a conventional magnetoresistance effect element which extends in the direction of applying the signal magnetic filed as is shown in
FIG. 2A
or in the opposite direction as shown in
FIG. 2A
, to acquire an improved sensitivity. Whichever direction the magnetoresistance effect element extends, however, no uniform bias magnetic field can be applied to the magnetoresistance effect element. This is because the magnetoresistance effect element has its resistance-changed with the angle between its axis of magnetization and the curved path of sense current. Consequently, the magnetoresistance effect element cannot provide a reliable output. It cannot be used in practice, particularly for tracks which are so narrow that the sense-current path is curved greatly.
Conventional magnetoresistance effect elements include a type constituted by two magnetic films sandwiching a nonmagnetic film as shown in
FIGS. 2B and 2C
(J. Appl. Phys. 53(3), 2596, 1982). Referring to
FIGS. 2B and 2C
, reference numeral 105 denotes a lower magnetic film;
106
, a nonmagnetic film;
107
, an upper magnetic film; and
108
a
and
108
b,
leads. In
FIGS. 2A and 2B
, a sense current flows into the lead
108
a
and out from the lead
108
b.
The magnetoresistance effect element with such an arrangement is affected by a magnetic field generated by a self-current. Assuming that a magnetic field generated by a current flowing through the lower magnetic film and the nonmagnetic film is applied to the upper magnetic film, the magnitude of the magnetic field generated by the self-current when the film thickness of each layer is equal to or smaller than the mean free path of conduction electrons is given by Relation (1) below. Note that the mean free path is approximately 300 Å for 300 K in the case of bulk Cu.
H
x1
to J*(t+d)/2  (1)
wherein J represents a current density, t represents a thickness of the upper magnetic film, and d represents a width of the upper magnetic film.
As an example, H
x
to 700 (A/m)=9 (Oe) when J=2×10
7
A/cm
2
, t=20 Å, and d=50 Å.
A magnetic field H
x2
applied to the lower magnetic film is given by H
x2
=−H
x1
because it is generated by a current flowing through the upper magnetic film and the nonmagnetic film.
Under these conditions, therefore, the magnetic moments (magnetizations) of the upper and lower magnetic films are antiparallel to each other if an anisotropic magnetic field of each layer is small (up to 3 Oe) like that of a thin permalloy film. However, a domain wall called an edge curling wall is pr

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