Magnetostriction measurement of GMR films on practical substrates

The magnetostriction constant λ_S of a magnetic film is usually measured by detecting the mechanical distortion of the film deposited on a thin glass substrate under an applied field using a laser beam. This method, however, cannot be applied to a film deposited on a rigid substrate such as Si and AlTiC used widely in real-world application. This is because that the distortion of the sample is too small to be detected. In addition, λ_S of the film deposited on the glass substrate sometimes differ from those of the film deposited on the Si or AlTiC substrate. Thus, it is very important to evaluate λ_S of a film deposited on an actual substrate. In this paper, a new method for measuring λ_S of a film deposited on a substrate used in actual products is proposed by detecting the change of the anisotropic field H_k of the film under bending load. λ_S can be calculated from the gradient of the applied mechanical stress dependence of the H_K. Utilizing this method, we have successfully measured λ_S of GMR films fabricated on the practical substrate by a very high resolution of 2×10^-8.