On the dynamics of the reentrant spin-glass state of the Fe100−xZrx (x = 9, 10) amorphous alloys

Abstract

Low temperature magnetization (M) and ac susceptibility (χac) data were used to investigate the reentrant spin-glass state in lengths of melt-spun ribbons of Fe100−xZrx (x = 9, 10) amorphous alloys. The temperature range investigated was from 2 to 300 K, while the applied magnetic field H was varied in the range of ±85 kOe. The magnetic properties were found to be strongly influenced by the sample composition despite the fact that the amount of Fe varies by 1 at. %. For instance, the Curie temperature (TC) is reduced from 232.5 K to 213.0 K with decreasing Fe concentration, while M for the lower Fe concentration, measured at the highest applied magnetic field (H = 85 kOe) was nearly double the value for that of the higher; the coercivity in the ferromagnetic regime is reduced by a factor close to five when x is increased from 9 at. % to 10 at. %. The ac susceptibility measured for frequencies f in the range of 10–104 Hz showed a sharp drop in the magnitude of the in-phase contribution (χac′) and a peak at the out-of-phase component (χac″), which shifts to higher temperatures with increasing values of f. The Voguel-Fulcher law applied to the χac″ data yielded an activation energy Ea/kB = 21.3 K (40.1 K), the glassy temperature TG = 15.5 K (38.2 K), and a relaxation time τ0=9.1×10−7 s (8.3×10−7 s), for the sample with x = 10 (x = 9). A plot of χac″ vs χac′ for a broad range of T and f yielded a broad maximum near the glassy temperature TG for both sample concentrations.