Magnetostriction of free layer in top-type and bottom-type spin-valve films

We investigated magnetostriction of a free layer in top-type and bottom-type spin valves. The magnetostriction of the free layer in the top-type spin valve increased as the thickness of free layer decreased, which can be attributed to the increase in the surface magnetic anisotropy. However, the magnetostriction of the free layer in the bottom-type spin valve exhibited no significant change with decreasing thickness of free layer, and was smaller than that of in the top-type spin valve. This difference may come from the degree of intermixing at the interface of the free layer. We confirmed by X-ray photoelectron spectroscopy that intermixing between the spacer and free layer, Cu and CoFeB respectively, can be quite different for the top-type and the bottom-type spin valves, and that the magnetostriction can be influenced by the degree of intermixing. The magnetostriction tends to be small value when intermixing is significant, as we found in the bottom-type spin valve.