Critical properties of the paramagnetic-to-ferromagnetic transition in nanocrystalline Gd diluted with Fe

Nanocrystalline Gd_0.946Fe_0.054 of average grain size 68 nm was prepared by melt-spinning. The magnetic behavior in the vicinity of the paramagnetic to ferromagnetic transition was investigated via dc magnetization and ac susceptibility measurements. The transition temperature and effective critical exponents for the order parameter and zero-field susceptibility were determined using ArrottNoakes and KouvelFisher analyses. The values obtained were T_C=291.71±0.07 K, β_eff= 0.385±0.009, and γ_eff=1.24±0.03, respectively. Correction to scaling analysis indicated that the asymptotic exponents were both smaller than the effective ones within the reduced-temperature range investigated, contrary to the behavior seen in monocrystalline Gd. This behavior can be explained in terms of a crossover from 3D short-range Heisenberg universality class to the 3D Ising universality class due to increased anisotropy induced by the high magnetic fields used in the measurements and also possibly due to strain.