Magnetic behavior of melt-spun gadolinium

Abstract

Melt-spun Gd is a structurally inhomogeneous system consisting of crystalline grains with an average size of $24\ifmmode\pm\else\textpm\fi{}3\text{ }\text{nm}$ that are separated by an amorphous interphase. This system exhibits a depression of ${T}_{C}$ $(289.70\ifmmode\pm\else\textpm\fi{}0.01\text{ }\text{K})$ relative to bulk Gd (293 K). The effective critical exponents (${\ensuremath{\beta}}_{\text{eff}}=0.389\ifmmode\pm\else\textpm\fi{}0.017$, ${\ensuremath{\gamma}}_{\text{eff}}=1.300\ifmmode\pm\else\textpm\fi{}0.014$, and $\ensuremath{\delta}=4.32\ifmmode\pm\else\textpm\fi{}0.02$) and critical amplitudes indicate that for the reduced-temperature range in this work, the paramagnetic-to-ferromagnetic transition is consistent with the isotropic dipolar universality class shown by bulk Gd. There is, however, evidence of enhanced anisotropy in the critical behavior of ms-Gd. Increasing random anisotropy in the intergrain regions with decreasing temperature below ${T}_{C}$ diminishes the coupling between the ferromagnetically ordered grains and produces a previously unobserved low-temperature peak in the imaginary part of the ac susceptibility. The random-anisotropy model provides a good description of the approach to saturation, which may result from the ferromagnetic correlation length becoming comparable to the anisotropy correlation length in the strong-field regime of the model.