Neutron scattering study of spin waves in the amorphous metallic ferromagnet (Fe93Mo7)80B10P10

Abstract

Low-angle inelastic-neutron-scattering experiments were performed on an amorphous ferromagnet of composition ${\left({\mathrm{Fe}}_{93}{\mathrm{Mo}}_7\right)}_{80}$ ${\mathrm{B}}_{10}$ ${\mathrm{P}}_{10}$ with $T_c=450\mathrm{}$ K. Well-defined spin waves were observed over the entire range of momentum transfer for which the scattering triangle could be closed ($q\le 0.25$ ${\mathrm{\AA }}^{-1\mathrm{}}$). The results were consistent with a normal ferromagnetic dispersion relation $h\omega \mathrm{}\left(q\right)=\Delta +D{q}^2+E{q}^4+\dots$, where the gap $\Delta$ can be largely accounted for by demagnetization effects. Low-temperature magnetization measurements were performed and fit to the relation $M\left(T\right)=M_0(1-B{T}^{\frac{3}{2}}-C{T}^{\frac{5}{2}})$. The measured long-wavelength spin waves account for only 70% of the density of magnon states necessary to explain $M\left(T\right)\mathrm{}$. For temperatures below 300 K, the mean spin-wave energies are well represented by the relation $〈\omega (q,T)〉=〈\omega \mathrm{}(q,0\mathrm{})\mathrm{}〉[1-0.612\mathrm{}{\left(\frac{T}{T_c}\right)}^{\frac{5}{2}}]$.