Magnetic properties of iron-rich Fe-Zr glasses

A systematic study of the magnetic properties of melt-spun amorphous ${\mathrm{Fe}}_{\mathrm{x}}$ ${\mathrm{Zr}}_{100\mathrm{-}\mathrm{x}}$ alloys with 88≤x≤93 using Mössbauer and magnetization measurements has established the magnetic phase diagram. The ordering temperature $T_c$ falls sharply with increasing x; below a second transition $T_{\mathrm{xy}}$, associated with the freezing of transverse-spin components, all the alloys order asperomagnetically ($T_{\mathrm{xy}}$<$T_c$). Hysteresis appears at still lower temperatures, but it is not directly related to the transverse-spin freezing. A $T^{1.3}$ variation of hyperfine field observed for T<$T_{\mathrm{xy}}$ is attributed to excitation of transverse magnetic modes. Contrary to the predictions of Heisenberg spin-glass theory, neither the ferromagnetic nor the asperomagnetic order appears to be long range. Extrapolation to x=100 indicates that pure amorphous iron would be a speromagnet with an iron moment of 1.7${\mu }_B$ and a spin-freezing temperature of order 150 K. Upon hydrogenation the magnetic structures of all the a-Fe-Zr alloys lose their noncollinear character, becoming good ferromagnets with Curie points in excess of 400 K.