Research Papers in Physics and Astronomy


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Published by American Physical Society. Phys. Rev. B. 77, 184415 2008. Copyright © 2008 American Physical Society. Permission to use.


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.

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