Critical behavior of an amorphous ferromagnet

In two separate experiments, the static magnetization and ac susceptibility of METGLAS® 2826A have been measured in the vicinity of the critical region, $2\times {10}^{-3\mathrm{}}<~t<~2\times {10}^{-1\mathrm{}}$, in applied fields up to 1 kOe. In the latter experiment, the critical behavior gives rise to peaks whose variation with magnetic field is shown to be governed uniquely by the index $\delta$. These two experiments, yield respectively, the following values for the critical indices: $\beta =0.42\mathrm{}\pm 0.04$, $\gamma =1.35\mathrm{}\pm 0.03$ with $\delta =4.3\mathrm{}\pm 0.2$; and $\gamma =1.49\mathrm{}\pm 0.06$ with $\delta =4.3\mathrm{}\pm 0.1$. Within experimental error they satisfy the scaling law relationship $\gamma =\beta (\delta -1)$ and are in good agreement with values deduced for other amorphous ferromagnets. They are also remarkably close to the values for the crystalline ferromagnetic elements Ni and Fe. The one unusual feature of these data concerns the effective value for $\gamma$ beyond the critical regime; in METGLAS® 2826A, and other amorphous ferromagnets, ${\gamma }^{*}\mathrm{}\left(T\right)\mathrm{}$ initially increases with increasing temperature above the transition, whereas in Ni it decreases continuously towards the high-temperature mean-field value of 1.