Proof of theT52term in the magnetization of Fe(BC) metallic glasses

Abstract

The magnetization of ${\mathrm{Fe}}_{80}{\mathrm{B}}_{20\ensuremath{-}x}{\mathrm{C}}_{x} (0\ensuremath{\le}x\ensuremath{\le}8)$ ferromagnetic metallic glasses has been measured in the temperature range $0<T\ensuremath{\lesssim}180$ K (corresponding to $0<\frac{T}{{T}_{C}}\ensuremath{\lesssim}0.3$) and in magnetic fields up to 40 kOe. As in crystalline ferromagnets, the magnetization obeys the equation $\frac{\ensuremath{\Delta}\ensuremath{\sigma}(T)}{\ensuremath{\sigma}(0)}=\ensuremath{\beta}{T}^{\frac{3}{2}}+\ensuremath{\gamma}{T}^{\frac{5}{2}}$. For the first time a clear necessity for the coefficient $\ensuremath{\gamma}$ even at lowest temperatures has been found in an amorphous series through bulk magnetization measurements. The concentration ($x$) dependence of the spin-wave stiffness constant $D$ is discussed. The range of exchange interactions in this amorphous series is of the order of 2 atomic distances, i.e., less than that in crystalline nickel.