Thickness induced crossover from the ferromagnetic to cluster spin glass state in Cr < inf > 70 < /inf > Fe < inf > 30 < /inf > thin films

Abstract

First five harmonics of the ac magnetic response were measuredas functions of temperature at different frequencies and with or without superposed dc magnetic field on Cr 70 Fe 30 thin films. An elaborate analysis of the linear susceptibility data reveals that (i) a well-defined paramagnetic (PM) to ferromagnetic (FM) phase transition, characterized by three-dimensional Heisenberg critical exponents, occurs for film thickness down to t 90 nm, and (ii) the film with t 40 nm exhibits experimental signatures in the critical region that are characteristic of both ferromagnets and spin glasses while the spin glass behavior dominates the FM one when t 20 nm.