Spin excitations in amorphous transition-metal boron glasses

Magnetic inelastic neutron scattering studies have been performed on ribbon specimens of amorphous Fe83B16.5Si0.5 and Fe20Ni60B19P1. The samples were prepared from isotopically enriched B to reduce the neutron absorption. The Curie temperatures for the two materials are 613 K and 410 K respectively, and the room temperature saturation magnetizations 4πMs are 16.0 kG and 5.1 kG. In the Fe20Ni60B19P1 specimen, well-defined spin waves were observed at room temperature for neutron wave-vector transfers in the range q=0.06 Å−1 to q=0.20 Å−1. After correcting for instrumental resolution, the data obeyed a quadratic dispersion law with spin stiffness D=80 meV-Å2. Spin waves in the Fe83B16.5Si0.5 amorphous alloy exhibited a D=125 meV-Å2 consistent with the higher Tc of this alloy.