Magnetic properties of iron-rich Fe-Zr glasses

Abstract

A systematic study of the magnetic properties of melt-spun amorphous ${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{Zr}}_{100\mathrm{\ensuremath{-}}\mathrm{x}}$ alloys with 88\ensuremath{\le}x\ensuremath{\le}93 using M\"ossbauer and magnetization measurements has established the magnetic phase diagram. The ordering temperature ${T}_{c}$ falls sharply with increasing x; below a second transition ${T}_{\mathrm{xy}}$, associated with the freezing of transverse-spin components, all the alloys order asperomagnetically (${T}_{\mathrm{xy}}$${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${\ensuremath{\mu}}_{B}$ 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.