Magnetic Behavior of Metamagnetic Dy Al<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Magnetization measurements have been carried out on a single crystal of DyAl${\mathrm{O}}_{3}$ at temperatures ($T$) between 1.2 and 300\ifmmode^\circ\else\textdegree\fi{}K. Consistent with earlier studies, the material was found to be antiferromagnetic below ${T}_{N}=3.5\ifmmode^\circ\else\textdegree\fi{}$K. Metamagnetic transitions were observed for fields ($H\ensuremath{\le}14.5$ kOe) applied in the (001) plane of the orthorhombic unit cell at $T=(1.45\ifmmode\pm\else\textpm\fi{}0.005)\ifmmode^\circ\else\textdegree\fi{}K$. The critical fields were in the range 5.9-11.3 kOe, depending on the angle $\ensuremath{\theta}$ between $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$ and the $a$ axis of the crystal. A two-step transition was observed in fields ($H\ensuremath{\le}60$ kOe) applied along the [110] direction at $T=1.2\ifmmode^\circ\else\textdegree\fi{}$K. The critical fields in this case were (6.5\ifmmode\pm\else\textpm\fi{}0.3) and (24.3\ifmmode\pm\else\textpm\fi{}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 $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$ in an appropriate direction. However, in a range of angles near the $b$ axis ($\ensuremath{\theta}\ensuremath{\gtrsim}73\ifmmode^\circ\else\textdegree\fi{}$), 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${\mathrm{O}}_{3}$.

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