Spin valve magnetoresistive device

A spin valve magnetoresistive multi-layered structure includes a first type magnetic layer which magnetization is free to rotate in accordance with an external applied magnetic field, a non-magnetic spacer layer adjacent to said first type magnetic film, and a second type magnetic layer adjacent to said non-magnetic film so that said second type magnetic layer is separated by said non-magnetic spacer layer from said first type magnetic layer, wherein said second type magnetic layer has a facet single crystal grain structure with a uniform crystal orientation whilst the first type magnetic layer is free of any facet single crystal grain structure with a uniform crystal orientation.

BACKGROUND OF THE INVENTION 
The present invention relates to a thin film exhibiting magnetoresistance 
effects for magnetic sensor such as magnetic head. Ferromagnetic such as 
permalloy which exhibits magnetoresistance effects have been on the use of 
various magnetic sensors such as magnetic heads. Magnetoresistance effects 
are the phenomenon of variation in electric resistance with application of 
a magnetic field. Such magnetoresistance effect alloy such as permalloy 
shows an anisotropic magnetoresistance effect of variation in electric 
resistivity depending upon a relative angle of an orientation of 
magnetization to a current direction. Permalloy thin films used for 
magnetic heads of magnetic recorders show an anisotropic magnetoresistance 
variation of 2-3%. 
In recent years, the requirement for high density magnetic recording has 
been on the increase. For satisfying this requirement, it has been 
required to develop a material showing a large magnetoresistance 
variation. A magnetic sensor such as magnetic head is required to detect a 
slight leakage of magnetic field from a magnetic recording medium, for 
which reason a material showing a large magnetoresistance variation under 
a small magnetic field, for example, not more than 100 Oe (Oersteds) (=8 
kA/m) is required for highly sensitive magnetic sensor. 
In recent years, magnetic multilayers (or superlattices) have been 
attracted as a material which realizes a giant magnetoresistance effect. 
In Journal of Applied Physics 67(9), May 1, 1990, pp. 50908-5913, it is 
disclosed that Fe(001)/Cr(001) superlattices with antiferromagnetic 
interlayer coupling exhibit a giant magnetoresistance at room temperature 
when an applied field aligns the magnetization of the Fe layers, the 
resistivity drops a factor of 2 and this giant magnetoresistance can be 
ascribed to the spin dependent scattering at interfaces. In Journal of 
Magnetism and Magnetic Materials 94, 1991, L1-L5, it is disclosed that 
Co/Cu multilayers with antiferromagnetic interlayer coupling exhibit a 
giant magnetoresistance at room temperature. Under the zero magnetic 
field, magnetic moments in the ferromagnetic metal layer (Fe or Co) 
intervened by the non-magnetic metal layer (Cr or Cu) 
antiferromagnetically align. With application of magnetic field, the 
magnetic moments in the ferromagnetic metal layers are changed to 
ferromagnetically align thereby electrical resistivity is dropped. This 
phenomenon is called as giant magnetoresistance effect which is different 
in mechanism from the anisotropic magnetoresistance effects of the 
permalloy. The above superlattice and multilayer structures have 
disadvantages in large exchange-interaction between the ferromagnetic 
layers which causes the orientation of the magnetization of the 
ferromagnetic layer is unlikely to be changed by an externally applied 
magnetic field. The magnetic field for saturation of the magnetoresistance 
is a few kOe to 10 kOe. Such superlattices and multilayers having large 
saturation magnetic fields are not available for highly sensitive magnetic 
sensor such as magnetic head. 
In order to satisfy the above disadvantages in large saturation magnetic 
fields with the magnetic superlattices and multilayers, spin valve 
magnetoresistance effect films have been proposed wherein two magnetic 
films are structurally and magnetically separated by a non-magnetic spacer 
layer. This spin valve structure is disclosed in Japanese laid-open patent 
publication Nos. 2-61572, 4-358310 and 6-60336. In the spin valve 
structure, first one of the two magnetic films allows the magnetization to 
be pined whilst second one of the two magnetic films allows the 
magnetization to rotate in accordance with an externally applied magnetic 
field. The first one is so called as a pined layer pining the 
magnetization and the second one is so called as a free layer allowing the 
magnetization to rotate freely. In the spin valve structure, the 
magnetoresistance varies depending upon the relative angle of the above 
pined and free layers. In order to pin the magnetization of one of the 
magnetic layers, it was proposed that two magnetic metal layers having 
different coercive forces from each other are provided to sandwich a 
non-magnetic spacer layer. This structure is disclosed in Applied Physics 
Letters, 59(2), Jul. 8, 1991, pp. 240-242. Fe--Co--Cu sandwich structure 
is used, wherein Fe layer is a first magnetic layer having a small 
coercive force whilst Co layer is a second magnetic layer having a large 
coercive force and Cu layer is a non-magnetic spacer layer. Alternatively, 
it was also proposed that two soft magnetic metal layers are provided to 
sandwich the non-magnetic spacer layer and an antiferromagnetic layer is 
further provided adjacent to one of the two soft magnetic metal layers so 
that the magnetization of the soft magnetic metal layer adjacent to the 
antiferromagnetic layer is pined by an exchange-bias magnetic field due to 
exchange-interaction from the antiferromagnetic layer whilst another soft 
magnetic metal layer separated by the non-magnetic spacer layer from the 
soft magnetic metal layer adjacent to the antiferromagnetic thin film 
allows magnetization to rotate freely in accordance with the external 
magnetic field. In Physical Review B, vol. 4, No. 1, Jan. 1, 1991, pp. 
1297-1300, it is disclosed that, in spin valve structure, Ni--Fe soft 
magnetic layers sandwich a Cu non-magnetic spacer layer and a Fe--Mn 
antiferromagnetic layer is provided adjacent to one of the Ni--Fe soft 
magnetic layers. Further alternatively, it was also proposed that two soft 
magnetic metal layers are provided to sandwich the non-magnetic spacer 
layer and an antiferromagnetic layer having a high electrical resistance 
and a large coercive force is further provided to contact with opposite 
ends of one of the two soft magnetic metal layers so that the 
magnetization of the soft magnetic metal layer in contact with the 
antiferromagnetic layer is pined whilst another soft magnetic metal layer 
separated by the non-magnetic spacer layer allows magnetization to rotate 
freely in accordance with the external magnetic field. In Japanese 
laid-open patent publication No. 6-325934, two Co--Fe soft magnetic metal 
layers are provided to sandwich a Cu non-magnetic spacer layer and a 
Co--Pt--Cr ferromagnetic metal layer having a high coercive force is 
provided to contact with one of the two Co--Fe soft magnetic metal layers. 
The above three type spin valve structures utilize conduction electrons to 
be scattered in one direction and show a magnetoresistance variation in 
the range of 5-10%. 
In order to obtain a further increase in the magnetoresistance variation, 
it was proposed that two non-magnetic spacer layers are provided to 
sandwich a free magnetic metal layer with magnetization to rotate freely 
in accordance with an externally applied magnetic field. Further two soft 
magnetic metal layers are provided to sandwich the two non-magnetic spacer 
layers sandwiching the free magnetic metal layer. Two ferromagnetic layers 
are provided adjacent to the two soft magnetic metal layers so as to pin 
the magnetization of the two soft magnetic metal layers whereby a 
symmetrical dual spin valve structure having five layered structure is 
formed. This is disclosed in Japanese laid-open patent publication No. 
6-223336. The symmetrical dual spin valve structure can utilize conduction 
electrons to be scattered in any directions. Another dual spin valve is 
further disclosed in Journal of Applied Physics 78(1), Jul. 1, 1995, pp. 
273-277. This symmetrical dual spin valve shows a large magnetoresistance 
effect exceeding 21%. 
The magnetoresistance effect of the above spin valve structure depends upon 
the relative angle of the magnetic moments between the two soft magnetic 
layers sandwiching the two non-magnetic metal layers sandwiching the 
magnetic layer with magnetization free to rotate in accordance with the 
externally applied magnetic field. The magnetoresistance effect is, 
however, independent from the current direction. The magnetoresistance 
effect of the spin valve is thus considered to be generated by an 
analogous mechanism to that of the above mentioned magnetic superlattices. 
The magnetoresistance effect of the above spin valve structure differ from 
the above mentioned magnetic superlattices in providing one or more 
non-magnetic spacer layers which has such a sufficient thickness as to 
suppress an interfacial exchange-coupling between the two soft magnetic 
layers. The spin valve structure is likely to show a relatively large 
magnetoresistance variation but not exceeding that of the artificial 
lattice structure such as superlattice structure. The spin valve structure 
shows an extremely small saturation magnetic field for saturating the 
magnetoresistance. This means that the spin valve structure is highly 
sensitive to a slight magnetic field. In Japanese laid-open patent 
publication No. 6-60336, it is disclosed that the spin valve structure 
comprises a multi-layered structure of glass/Co(6 nm)/Cu(3.4 nm)/Fe--Mn(10 
nm)/Cu(1 nm), which shows a large magnetoresistance variation of 8.7% 
under a small magnetic field in the range of 20-120 Oersteds. In the above 
second spin valve structure, the antiferromagnetic layer is used as an 
exchange-coupled film to pin the magnetization of one of the two magnetic 
layers whilst the other magnetic layer allows the magnetization to rotate 
freely in accordance with the externally applied magnetic field. This 
second type spin valve structure is superior in properties and 
facilitation of processing the same into a magnetic head, for which reason 
developments of the second type spin valve structure are more active. 
The above antiferromagnetic exchange-coupled layer is the essential layer 
for the spin valve films. This antiferromagnetic exchange-coupled layer is 
required both to have a superior corrosion resistance and to provide a 
sufficiently large exchange-coupling magnetic field to the soft magnetic 
layer adjacent to the antiferromagnetic exchange-coupled layer. Fe--Mn 
alloy is capable of providing a large exchange-coupling magnetic field in 
the range of 200-400 Oersteds for pinning the magnetization of the 
adjacent soft magnetic layer and also gives a stable magnetoresistance. 
Nevertheless, Fe--Mn alloy is inferior in corrosion resistance, for which 
reason if Fe--Mn alloy is applied to the antiferromagnetic 
exchange-coulped layer included in the spin valve films, it is difficult 
to ensure a sufficient high reliability of the magnetic head using the 
spin valve films. 
In Japanese laid-open patent publication No. 7-220246, it is disclosed 
that, in place of the Fe--Mn antiferromagnetic exchange-coupled layer for 
spin valve films, a NiO film is used as the antiferromagnetic 
exchange-coupled layer in the spin valve film. Namely, the 
antiferromagnetic oxide exchange-coupled layer is used for spin valve 
films. In Japanese laid-open patent publication No. 7-202292, it is also 
disclosed that, in place of the Fe--Mn antiferromagnetic exchange-coupled 
layer for spin valve films, NiO/CoO superlattice structure is used as the 
antiferromagnetic exchange-coupling layer in the spin valve film. Namely, 
the antiferromagnetic oxide exchange-coulpled layer is used for spin valve 
films. The antiferromagnetic oxide is superior in corrosion resistance. 
Such antiferromagnetic oxide exchange-coupled layers are capable of 
providing small exchange-bias magnetic fields of approximately 100 
Oersteds which is insufficient for pinning the magnetization of the soft 
magnetic layer adjacent to the antiferromagnetic oxide exchange-coupled 
layer because the maximum leakage magnetic field from the magnetic medium 
may exceed 100 Oersteds. If the antiferromagnetic oxide exchange-coupled 
layer is used in the spin valve films for the magnetic head, then the 
magnetization of the soft magnetic layer adjacent to the antiferromagnetic 
oxide exchange-coupling layer may rotate in accordance with such a large 
leakage magnetic field as exceeding 100 Oersteds from the magnetic medium 
although the magnetization should have to be pinned by the exchange-bias 
magnetic field provided by the antiferromagnetic oxide exchange-coupled 
layer. This means that the operations of the magnetic head is unstable. 
In the above circumstances, it had been required to develop a novel 
magnetoresistive spin valve multi-layered structure showing stable 
performances and properties. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a novel 
spin valve multi-layer structure showing a large magnetoresistance, which 
is free from the disadvantages and problems as described above. 
It is a further object of the present invention to provide a novel spin 
valve device showing a large magnetoresistance variation under a small 
magnetic field which is free from the disadvantages and problems as 
described above. 
The above and other objects, features and advantages of the present 
invention will be apparent from the following descriptions. 
The first present invention provides a spin valve magnetoresistive 
multi-layered structure including a first type magnetic layer which 
magnetization is free to rotate in accordance with an external applied 
magnetic field, a non-magnetic spacer layer adjacent to said first type 
magnetic film, and a second type magnetic layer adjacent to said 
non-magnetic film so that said first type magnetic layer is separated by 
said non-magnetic spacer layer from said second type magnetic layer, 
wherein said second type magnetic layer has a facet single crystal grain 
structure with a uniform crystal orientation whilst the first type 
magnetic layer is free of any facet single crystal grain structure with a 
uniform crystal orientation. 
The second present invention provides a spin valve magnetoresistive 
multi-layered structure including a first type magnetic layer which 
magnetization is free to rotate in accordance with an external applied 
magnetic field, a non-magnetic spacer layer adjacent to the first type 
magnetic film, a second type magnetic layer adjacent to the non-magnetic 
film so that the first type magnetic layer is separated by the 
non-magnetic spacer layer from the second type magnetic layer, and a 
ferromagnetic layer adjacent to the second type magnetic layer wherein the 
ferromagnetic layer has a facet single crystal grain structure with a 
uniform crystal orientation whilst the first type magnetic layer is free 
of any facet single crystal grain structure with a uniform crystal 
orientation. 
The third present invention provides a spin valve magnetoresistive 
multi-layered structure including a first type magnetic layer which 
magnetization is free to rotate in accordance with an external applied 
magnetic field, a non-magnetic spacer layer adjacent to the first type 
magnetic film, a second type magnetic layer adjacent to the non-magnetic 
film so that the first type magnetic layer is separated by the 
non-magnetic spacer layer from the second type magnetic layer, and a 
non-magnetic layer adjacent to the second type magnetic layer wherein the 
non-magnetic layer has a facet single crystal grain structure with a 
uniform crystal orientation, whilst the first type magnetic layer is free 
of any facet single crystal grain structure with a uniform crystal 
orientation. 
The fourth present invention provides a spin valve magnetoresistive device 
including a substrate and a multi-layered structure formed on the 
substrate. The multi-layered structure comprises a first type magnetic 
layer which magnetization is free to rotate in accordance with an external 
applied magnetic field, a non-magnetic spacer layer extending on a bottom 
surface of the first type magnetic film, and a second type magnetic layer 
extending on a bottom surface of the non-magnetic film so that the first 
type magnetic layer is separated by the non-magnetic spacer layer from the 
second type magnetic layer. The second type magnetic layer extends on a 
top surface of the substrate, wherein the second type magnetic layer has a 
facet single crystal grain structure with a uniform crystal orientation 
whilst the first type magnetic layer is free of any facet single crystal 
grain structure with a uniform crystal orientation. 
The fifth present invention provides a spin valve magnetoresistive device 
including a substrate and a multi-layered structure formed on the 
substrate. The multi-layered structure comprises a first type magnetic 
layer which magnetization is free to rotate in accordance with an external 
applied magnetic field, a non-magnetic spacer layer extending on a bottom 
surface of the first type magnetic film, a second type magnetic layer 
extending on a bottom surface of the non-magnetic film so that the first 
type magnetic layer is separated by the non-magnetic spacer layer from the 
second type magnetic layer, and a ferromagnetic layer extending on a 
bottom surface of the second type magnetic layer. The ferromagnetic layer 
extends on a top surface of the substrate, wherein the ferromagnetic layer 
has a facet single crystal grain structure with a uniform crystal 
orientation whilst the first type magnetic layer is free of any facet 
single crystal grain structure with a uniform crystal orientation. 
The sixth present invention provides a spin valve magnetoresistive device 
including a substrate and a multi-layered structure formed on the 
substrate. The multi-layered structure comprises a first type magnetic 
layer which magnetization is free to rotate in accordance with an external 
applied magnetic field, a non-magnetic spacer layer extending on a bottom 
surface of the first type magnetic film, a second type magnetic layer 
extending on a bottom surface of the non-magnetic film so that the first 
type magnetic layer is separated by the non-magnetic spacer layer from the 
second type magnetic layer, and a non-magnetic layer extending on a bottom 
surface of the second type magnetic layer. The non-magnetic layer extends 
on a top surface of the substrate, wherein the non-magnetic layer has a 
facet single crystal grain structure with a uniform crystal orientation, 
whilst the first type magnetic layer is free of any facet single crystal 
grain structure with a uniform crystal orientation.