Finite-size scaling in band ferromagnets with non-universal critical behavior

Abstract

The ultra-high sensitivity of the ferromagnetic resonance (FMR) techniquehas been fully exploited to study the finite-size effects in the criticalregion near the ferromagnetic to paramagnetic phase transition inCr75−xFe25+x (x = 0, 5) thin films of high structural and magnetic quality. Conclusiveexperimental evidence is provided for the validity of finite-size scaling.Irrespective of the film thickness and composition, the critical exponentsβ,γ andν for spontaneous magnetization, initial magnetic susceptibility and spin–spin correlationlength retain their bulk values so that no dimensionality crossover occurs within the filmthickness range covered in the FMR experiments. The present results indicate that (i) likeCr75−xFe25+x, the previously studiedFe, Co, Ni, and CoNi3 thin films behave as itinerant-electron (band) ferromagnets inwhich the isotropic long-range interactions between spins decay asJ(r)∼r−(d+σ) (σ>0), and (ii) the latticedimensionality d,spin dimensionality m, and range of spin–spin interactions (via the material-specific parameterσ) decide the (non-universal) values of the critical exponents.