Magnetization and Mössbauer study of the reentrant amorphousFe90Zr10alloy

A detailed analysis of the magnetization and ‘‘zero-field’’ Mössbauer data taken on the amorphous ${\mathrm{Fe}}_{90}$ ${\mathrm{Zr}}_{10}$ alloy in the temperature range 4.2–300 K reveals the following: (i) Spin-wave (SW) excitations at low temperatures, single-particle (SP) excitations and local-spin-density (LSD) fluctuations over a wide range of intermediate temperatures, and enhanced fluctuations in the local magnetization for temperatures close to the Curie temperature, ${\mathit{T}}_{\mathit{C}}$, contribute dominantly to the thermal demagnetization of spontaneous magnetization; (ii) SW modes soften at temperatures below the freezing temperature ${\mathit{T}}_{\mathit{f}}$, where long-range ferromagnetic order coexists with the cluster spin-glass order; (iii) the LSD fluctuations are completely suppressed when magnetic fields (H) higher than 5 kOe are applied and M(H,T) for H>5 kOe is solely governed by the SW and SP excitations for temperatures up to 0.95${\mathit{T}}_{\mathit{C}}$; (iv) contrary to some earlier claims, the spin-wave stiffness coefficient does not depend on H in the field range 5 kOe≤H≤15 kOe; (v) the magnetic hyperfine-field distribution, P(${\mathit{H}}_{\mathrm{hf}}$), is bimodal and comprises two Gaussian distributions; (vi) the low-field spin fraction [ratio of the area under the low-field Gaussian curve to that under the P(${\mathit{H}}_{\mathrm{hf}}$)-vs-${\mathit{H}}_{\mathrm{hf}}$ curve] grows at the expense of the high-field spin fraction as the temperature is raised above T≃150 K and amounts to about 90% of the total Fe spins for T≃${\mathit{T}}_{\mathit{C}}$; and (vii) the spin-freezing process does not start abruptly at ${\mathit{T}}_{\mathit{f}}$ but proceeds gradually over a wide temperature range extending from 130 K (≊3${\mathit{T}}_{\mathit{f}}$) down to 4.2 K. While the transverse spin freezing and the finite spin clusters (composed of antiferromagnetic Fe spins) plus ferromagnetic (FM) matrix models fail to explain some of our findings, the finite-FM-clusters–FM-matrix picture provides a satisfactory explanation for all the diverse aspects of the present results.