Magnetic properties of gadolinium ortho-aluminate

An account is given of specific heat, magnetic susceptibility and magnetic moment measure­ments on gadolinium ortho-aluminate, GdAlO3, at temperatures in the liquid helium range. This compound orders antiferromagneticallv at 3.87 K. In the antiferromagnetic state, its properties can be accounted for satisfactorily as those of an array of S-state magnetic ions with isotropic magnetic properties, coupled together by exchange interaction between nearest neighbours and subject to a ‘single ion’ anisotropy force due to the crystalline electric field. Because the structure approximates closely to a simple cubic lattice of Gd3+ ions, magnetic dipole effects have little influence on the ordering. The exchange and anisotropy forces are calculated from the experimental data, and the measured properties are compared with various theoretical predictions for a simple two sublattice antiferromagnet. The variation of the specific heat in the critical region close to the Néel point is compared with that of other compounds undergoing magnetic transitions at low temperatures, and a consistent pattern of behaviour is found.