Coating processes – Magnetic base or coating – Magnetic coating
Reexamination Certificate
1999-09-07
2001-05-29
Pianalto, Bernard (Department: 1762)
Coating processes
Magnetic base or coating
Magnetic coating
C204S192220, C427S127000, C427S131000, C427S132000, C427S265000, C427S271000, C427S404000, C427S419200
Reexamination Certificate
active
06238731
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a thin-film magnetic head having a head face and comprising a magnetoresistive element oriented transversely to the head face and a flux-guiding element of a magnetically permeable material terminating in the head face, a peripheral area of the magnetoresistive element extending parallel to the head face being present opposite the flux-guiding element for forming a magnetic connection between the magnetoresistive element and the flux-guiding element.
A magnetic head of this type is known from U.S. Pat. No. 4,425,593 herewith incorporated by reference. The known magnetic head is a read head which is used for detecting magnetic fields representing information on a magnetic recording medium moving with respect to the magnetic head, particularly a magnetic tape. The magnetic head comprises a ferrite substrate which constitutes a magnetic yoke together with two aligned layer-shaped flux guides of a nickel-iron alloy. The magnetic head also comprises an elongate layer-shaped magnetoresistive element (MR element) provided with equipotential strips, which element has contact faces at two opposite ends and has such a magnetic anisotropy that the easy axis of magnetization at least substantially coincides with its longitudinal axis. The MR element is arranged within the magnetic yoke in such a way that a gap present between the flux guides is bridged by the MR element. The flux guides have facing end portions which are present opposite peripheral areas of the MR element extending parallel to the longitudinal axis. A quartz insulation layer extends between the ferrite substrate and the electrically conducting MR element and between the MR element and the electrically conducting flux guides. In the known magnetic head a non-magnetic material is thus present in the overlap areas constituted by the peripheral areas of the MR element and the facing end portions of the flux guides.
A drawback of the known magnetic head is that, due to the distance between the peripheral areas of the MR element, which distance is caused by the non-magnetic material, and the opposite end portions of the flux guides, only a small part of the magnetic flux originating from the magnetic recording medium is actually passed through the MR element. In other words, the known magnetic head has a low efficiency.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to improve the efficiency of the magnetic head mentioned in the opening paragraph.
To this end the magnetic head according to the invention is characterized in that the peripheral area of the magnetoresistive element and the flux-guiding element constitute a common magnetic contact face, the magnetically permeable material of the flux-guiding element being electrically insulating. Consequently, in the magnetic head according to the invention a flux-guiding element of an electrically insulating material is used, with the peripheral area of the magnetoresistive element (MR element) engaging an end portion of the flux-guiding element directly, i.e. without any intermediate layer. This results in a direct magnetic coupling between the MR element and the flux-guiding element, which leads to an achievable high efficiency. It has been found that an increase of the efficiency by a factor of 3 is feasible as compared with the efficiency of the known magnetic head. Similarly as in the known magnetic head, the MR element of the magnetic head according to the invention has contact faces.
The required resistivity of the magnetically permeable material of the flux-guiding element is substantially determined by the admissible loss of sensitivity resulting from a possible modification of the resistance between the contact faces of the MR element due to the direct connection between the MR element and the flux-guiding element. In this respect it has been found that reasonable to very good results can be achieved if the material of the flux-guiding element is an oxidic soft-magnetic material. For example, the reasonably electrically insulating ferrite Fe
3
O
4
is suitable for use as a material for the flux-guiding element. It is true that this causes a small decrease of the resistance between the contact faces of the MR element, but this decrease does not lead to unacceptable losses of sensitivity in the case of suitably chosen dimensions. However, an embodiment of the magnetic head according to the invention is preferred in which the oxidic soft-magnetic material is an MnZn ferrite or an NiZn ferrite. These ferrites have such a high resistivity that losses of sensitivity due to the flux-guiding element being in electrical contact with the MR element cannot be observed in practice.
It is to be noted that the magnetic head according to the invention provided with a flux-guiding element of ferrite has the further advantage that the corrosion and wear resistance of the head face are improved with respect to a head face of a known magnetic head provided with a metal flux guide.
An embodiment of the magnetic head according to the invention is characterized in that the oxidic soft-magnetic material is a garnet. Garnets form a group of materials that are very suitable for use as magnetic flux conductors. They possess proper mechanical and electrical properties, while the magnetic properties can be tuned by adding dopants to reduce the magnetic anisotropy. The chemical properties of garnets facilitate deposition in thin film form of the compounds in the proper oxygen state. A suitable material is Co/Si doped YIG (Y
3
Fe
5
O
12
) described in IEEE Transactions on Magnetics, Vol. Mag. 6, no. 3, September 1970, Nicolas et al, p. 608-610 (herewith incorporated by reference), which material has a magnetic permeability of at least 500. Other doped garnets e.g. disclosed in Journal of Magnetism and Magnetic Materials 125 (1993) L23-28, Pascard et al (herewith incorporated by reference) are also suitable.
An embodiment of the magnetic head according to the invention is characterized in that the MR element terminates in the head face, with the flux-guiding element being formed by a substrate. In this embodiment the MR element is directly provided on the substrate comprising preferably MnZn ferrite or NiZn ferrite. Also in this embodiment there are small magnetic and electrical losses.
An embodiment of the magnetic head according to the invention, which has a satisfactory efficiency and at least a reasonable, practically usable sensitivity, is characterized in that the magnetically permeable material of the flux-guiding element satisfies the condition
ρ
f
=
c
·
[
t
1
·
h
1
t
m
·
b
]
·
ρ
m
in
which
c
is
a
numerical
value
of
more
than
1
/
3
ρ
f
is
the
resistivity
of
the
material
of
the
flux
-
guiding
element
ρ
m
is
the
resistivity
of
the
material
of
the
magnetoresistive
element
t
1
is
the
thickness
,
viewed
in
a
direction
transverse
to
the
magnetoresistive
element
,
of
the
flux
-
guiding
element
,
t
m
is
the
thickness
of
the
magnetoresistive
element
,
h
1
is
the
height
,
viewed
from
the
head
face
,
of
the
flux
-
guiding
element
and
b
is
Cillessen Johannes F. M.
Folkerts Wiepke
Postma Lambertus
Ruigrok Jacobus J. M.
Van Der Zaag Pieter J.
Belk Michael E.
Pianalto Bernard
U.S. Philips Corporation
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