Antiferromagnetism and the Magnetic Phase Diagram of GdAlO3

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°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 Néel temperature is found to be 3.89°K and the Curie-Weiss $\Theta =-4.6\mathrm{}$°K. The gradient of the inverse molar susceptibility shows the ionic moment of Gd to be $7 {\mu }_B$, but this full moment is never observed in the high-field magnetization, even in fields of 200 kOe at 1.3°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 $H-T$ 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.