FERROMAGNETISM IN GADOLINIUM TRICHLORIDE

Susceptibility and magnetization measurements were made on single crystals of GdCl/sub 3/ in the temperature range 1.5 to 20 deg K. The results indicate that this substance becomes ferromagnetically ordered at 2.2 deg K. Measurements were made on a number of differently shaped samples, both parallel and perpendicular to the crystallographic c-axis, in order to establish the direction of ferromagnetic alinement and to verify that the susceptibility in this direction is 1/N, (N is the demagnetizing factor), as expected for a spontaneously magnetic material in which the domains can move freely. To exclude the possibility that the ordering is ferri- rather than truly ferro-magnetic, magnetization measurements were made in fields large enough to remove the domains, but small compared with the internal ordering fields. The results extrapolated to T = 0 deg K show that the spontaneous moment is at least 80% of the predicted 7 mu /sub BETA // ion, the discrepancy being tentatively ascribed to zeropoint disorder produced by the relatively large dipolar interactions. Magnetic dipole interactions also account satisfactorily for the observed anisotropy as deduced from magnetization measurements made with fields perpendicular to the easy axis. (auth)