Antiferromagnetism and the Magnetic Phase Diagram of GdAlO3

Abstract

Measurements of the magnetization and differential susceptibility of GdAl${\mathrm{O}}_{3}$ have been made in pulsed magnetic fields in the temperature range 1.3-100\ifmmode^\circ\else\textdegree\fi{}K. It is found that GdAl${\mathrm{O}}_{3}$ is a uniaxial antiferromagnet with the easy axis of magnetization along the orthorhombic $b$ axis. The N\'eel temperature is found to be 3.89\ifmmode^\circ\else\textdegree\fi{}K and the Curie-Weiss $\ensuremath{\Theta}=\ensuremath{-}4.6$\ifmmode^\circ\else\textdegree\fi{}K. The gradient of the inverse molar susceptibility shows the ionic moment of Gd to be $7 {\ensuremath{\mu}}_{B}$, but this full moment is never observed in the high-field magnetization, even in fields of 200 kOe at 1.3\ifmmode^\circ\else\textdegree\fi{}K. The differential susceptibility has been used to observe both the antiferromagnetic-to-spin-flop and the spin-flop-to-paramagnetic phase transitions, and to determine the phase diagram in the $H\ensuremath{-}T$ plane. The molecular-field parameters have been calculated from the antiferromagnetic-to-spin-flop transition and the angular variation of the spin-flop-to-paramagnetic transition.