Spin excitations in amorphous transition-metal boron glasses

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Abstract
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.