The present invention relates to magneto-resistance effect devices, and in particular, magneto-resistance effect films. Such films can be used for magnetic field detection, e.g., in a playback head for a magnetic disk device or a magnetic field sensor.
Magneto-resistance effect films, exhibiting magneto-resistance (MR) effect, are employed as devices for detecting magnetic fields, and are widely employed in the field of magnetic sensors or magnetic heads.
Up to now, an Fe-Ni alloy film (so-called permalloy film) has been mainly used as the magneto-resistance effect film. However, permalloy film has only a small rate of change of magneto-resistance such that a magnetic head employing a permalloy film cannot be said to have sufficient sensitivity for coping with anticipated high density recording.
An artificial lattice film having a lamination of a magnetic film of Fe and a conductor film (non-magnetic film) of Cr has been reported to have the rate of change of magneto-resistance amounting to multiples of ten percent. See, Physical Review letters, vol. 61, page 2472, 1988. This is referred to as the Giant Magneto-Resistance (GMR) effect. There are high expectations of applying GMR to magneto-resistance devices.
In addition to the combination of the Fe layer and the Cr layer, the combination of a magnetic film of Co and a non-magnetic film of Cu has also be reported to exhibit the giant magneto-resistance effect. See, Physical Review letters, vol.66, page 2152, 1991.
It has also been reported that, by employing an alloy of three elements, namely iron, nickel and cobalt, in a layer of a magnetic material, a larger change in resistance may be produced for a small change in the magnetic field, such that sensitivity to an external magnetic field may be improved and hence the artificial lattice film is effective from the practical standpoint.
It has also been reported that the giant magneto-resistance effect can be achieved with a laminated film consisting of a magnetic layer, a conductor layer and a magnetic layer, in that order. This is a so-called spin bulb film. See, Journal of Magnetism and Magnetic Materials, vol.93, page 101, 1991.
However, a magneto-resistance effect film, having the above-described laminated film structure, is susceptible to diffusion among respective films due to heat. Thus, the above disclosed magneto-resistance effect films have a drawback that magneto-resistance effect characteristics tend to deteriorate under elevated temperatures.
This deterioration in the magneto-resistance effect can be caused by current flowing through the MR device at a high current density during operation of the device. This is possibly ascribable to the fact that the current flowing at a high current density during the operation leads to heat evolution and to a disturbed array of magnetization in the multi-layer magneto-resistance effect film construction.