Dynamic susceptibility of reentrant Fe-rich inhomogeneous amorphous alloys

Melt-spun amorphous alloys of Fe₉₁Zr₉, Fe₉₁Zr₇B₂, Fe₉₀Zr₇B₃ and Fe₈₈Zr₈B₄ have been characterized by AC susceptibility at frequencies between 30 Hz and 10 KHz. The measurements reflect the existence of reentrant spin glass transitions below 40 K for all cases. The transition shift per frequency decade is large compared to the observed in conventional spin-glass alloys. The shift value increases with the boron content and becomes closer to values in fine-particle systems. We find that the relaxation in Fe₉₁Zr₉ follows a critical slowing down at the reentrant transition, with exponents and . The non-linear susceptibility displays a peak at the transition in this alloy, but wider than in canonical spin glasses. A Vogel-Fulcher (VF) activation process can explain the frequency variation in all the Fe-Zr-B alloys. The reduction of the ideal glass temperature in the VF approach, found in the higher Boron content alloys, is an indication of a superparamagnetic-like behavior. The behavior shown by these alloys is intermediate between a collective freezing and superparamagnetic-like relaxation. We propose that this is arising due to a heterogeneous spin structure. The inclusion of a reduced amount of B, affects the magnetic spin structure.Received: 13 May 2003, Published online: 22 September 2003PACS: 75.50.Lk Spin glasses and other random magnets - 75.50.Kj Amorphous and quasicrystalline magnetic materials - 75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)J.S. Garitaonandia: Present address: Dept. Física Aplicada, F. Ciencias, Universidad del País Vasco, Bilbao 48080, Spain