Melt-spun Gd is a structurally inhomogeneous system consisting of crystalline grains with an average size of 24±3 nm that are separated by an amorphous interphase. This system exhibits a depression of TC (289.70±0.01 K) relative to bulk Gd (293 K). The effective critical exponents (βeff =0.389±0.017, γeff =1.300±0.014, and δ=4.32±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 TC 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.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - May 14 2008|