Soft magnetic characteristics of an ultrathin CoFeNi free layer in spin-valve films

We have investigated the soft magnetic characteristics of all ultrathin Co-rich CoFeNi free layer in spin-valve films. By addition of Ni to a Co-rich CoFe free layer, magnetostriction (lambda) of the films increased positively with Ni concentration, in contrast to which a Co90Fe10 free layer showed a negatively large lambda. However, Ni addition also caused,in increase in coercivity of the easy axis direction (H-c(e.a.)). To avoid this problem, a slight decrease in the Co contents Ora CoFeNi free layer was found to be effective for decreasing H-c(e.a.). In order to satisfy both the small lambda and H-c(e.a.), a free layer Of (Co86Fe14)(88-94)Ni12-6 proved to be an optimum composition in spin-valve films. Moreover, the zero lambda composition of the CoFeNi free layer was changed by a high-conductance Cu layer deposited on the free layer, which was considered to come from the lattice strain of a free layer. (C) 2005 Elsevier B.V. All rights reserved.