Magnetic Behavior of Metamagnetic Dy AlO3

Magnetization measurements have been carried out on a single crystal of DyAl${\mathrm{O}}_3$ at temperatures ($T$) between 1.2 and 300°K. Consistent with earlier studies, the material was found to be antiferromagnetic below $T_N=3.5\mathrm{}°$K. Metamagnetic transitions were observed for fields ($H\le 14.5$ kOe) applied in the (001) plane of the orthorhombic unit cell at $T=(1.45\mathrm{}\pm 0.005)°K$. The critical fields were in the range 5.9-11.3 kOe, depending on the angle $\theta$ between $\overrightarrow{\mathrm{H}}$ and the $a$ axis of the crystal. A two-step transition was observed in fields ($H\le 60$ kOe) applied along the [110] direction at $T=1.2\mathrm{}°$K. The critical fields in this case were (6.5±0.3) and (24.3±1.2) kOe for the two steps in the magnetization curve. The data showed that any of the four magnetic sublattices in DyAl${\mathrm{O}}_3$ may be reversed selectively by applying $\overrightarrow{\mathrm{H}}$ in an appropriate direction. However, in a range of angles near the $b$ axis ($\theta \gtrsim 73°$), the favored transition involves a reversal of the magnetization simultaneously on two of the sublattices. Expressions for critical fields were derived theoretically and fitted to the data, yielding estimates of the internal fields in DyAl${\mathrm{O}}_3$. These estimates were compared to values derived earlier in published optical studies of DyAl${\mathrm{O}}_3$, and to analogous quantities in the isomorphous compounds GdAl${\mathrm{O}}_3$ and TbAl${\mathrm{O}}_3$.