Effect of ferromagnetic proximity on critical behavior

Abstract

We have investigated the magnetic phase transition in amorphous Fe${}_{93}$Zr${}_{7}$($x$ \AA{})/Co${}_{95}$Zr${}_{5}$(1 \AA{}) multilayers, where $x=25$, 50, and 75. The extremely thin CoZr layer induces magnetic order at temperatures well above the inherent ordering temperature of Fe${}_{93}$Zr${}_{7}$. The changes in the critical exponent $\ensuremath{\beta}$, associated with the temperature dependence of the magnetization, imply a crossover from two- to three-dimensional behavior as the FeZr thickness is reduced, consistent with a substantial magnetic induction in the FeZr layers. In addition we determined the exponents $\ensuremath{\delta}$ and $\ensuremath{\gamma}$, of the critical isotherm and the susceptibility, respectively, and their values confirm the nonuniversal character of the phase transition. Scaling of the results yields an excellent data collapse and is found to hold in the crossover regime where the universality hypothesis is not applicable.