Magnetoresistive measurement of magnetostriction in Permalloy

The authors demonstrate a simple technique for determining magnetostriction in Permalloy films. It is capable of measuring values as low as ±(1×10^-7) in unpatterned films or patterned microstripes as thin as 10 nm. The method utilizes the inverse magnetostriction effect, using magnetoresistive detection to measure changes in film anisotropy induced by application of anisotropic strain. Samples are prepared in bar form, the center of which is deflected in a bending fixture in order to generate strain on the film. The determination of magnetostriction involves measurement of the width of the magnetoresistance versus applied field transfer characteristic of the film stripe as a function of bar center deflection using a simple benchtop apparatus. The technique is used routinely to measure magnetostriction both in as-deposited films and in fully processed magnetoresistor elements for use in magnetic recording applications