Neutron depolarization in a reentrant spin-glass system: Amorphous Fe-Mn

Abstract

Polarization analysis of the transmitted beam has been performed in a reentrant spin-glass system (${\mathrm{Fe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$${)}_{75}$${\mathrm{P}}_{16}$${\mathrm{B}}_{6}$${\mathrm{Al}}_{3}$ for several concentrations x starting from the true ferromagnet to the true spin glass. The influence of some important parameters like the temperature, the sample thickness, the neutron wavelength, and the applied magnetic field, as well as the cooling conditions, has been checked. Large ferromagnetic domains of about 30 \ensuremath{\mu}m size are evident in the nonfrustrated alloy (x=0.07). In the weakly frustrated samples (0.22x0.26), smaller domains of about 4 to 6 \ensuremath{\mu}m are observed, which persist at low temperature. In the strongly frustrated x=0.30 sample, we observe a decrease of the domain size or of the internal magnetization at low temperature. The results in the weakly frustrated alloys support the coexistence at low temperature of a long-range longitudinal order together with frozen transverse spin components, in good agreement with the mean-field predictions. The limits of the infinite-range mean-field model are shown in the sample close to the critical point.