Anomalous magnetization of amorphous Tb${\mathrm{Fe}}_2$, Gd${\mathrm{Fe}}_2$, and Y${\mathrm{Fe}}_2$

Magnetization data are presented on sputter-deposited amorphous $R {\mathrm{Fe}}_2$ materials, where $R$ represents the rare-earth elements Tb, Gd, and Y. Both the Tb and Gd compounds exhibit ferrimagnetic order with Curie temperatures approximately 40% lower than the equivalent crystalline Laves phase compounds. The 0 K saturation magnetizations of the Gd amorphous and crystalline materials are both equal to 3.9${\mathrm{\mu }}_{\mathit{B}}$, while in the Tb${\mathrm{Fe}}_2$ the magnetization is significantly lower in the amorphous phase (4.2${\mathrm{\mu }}_{\mathit{B}}$ vs 5.4${\mathrm{\mu }}_{\mathit{B}}$ for crystalline Tb${\mathrm{Fe}}_2$). The Y${\mathrm{Fe}}_2$ exhibits no long-range magnetic order above 3.5 K. At low temperatures large "coercive" fields appear for the Tb${\mathrm{Fe}}_2$ and increase greatly in magnitude at temperatures below 40 K, reaching 30 kG at 4 K. A possible model to explain this and other effects associated with a large random-directional local anisotropy field is presented.