LOW-TEMPERATURE MAGNETIC PROPERTIES OF SOME HEXAGONAL RARE-EARTH TRIHALIDES

We have made measurements of the low-temperature heat capacity, magnetic susceptibility, and chlorine nuclear quadrupole resonance (NQR) of CeCl3, PrCl3, NdCl3, SmCl3, and CeBr3. Some measurements have been made on PrBr3 and NdBr3. The experimental results can be closely correlated with antiferromagnetic linear chain models. The NQR shows that long-range order occurs in PrCl3 at 0.428 K. In NdCl3, the NQR line disappeared at 0.50 K and the resonances produced by an internal field appeared at 0.17 K. In CeCl3, the NQR resonance disappeared at 0.110 K and no lines were found above 0.054 K. In SmCl3, the NQR line disappeared at 0.21 K and no resonance was observed above 0.1 K. We have measured the internal field, which is proportional to the sublattice magnetization, at the chlorine nucleus in PrCl3 and NdCl3 below their Néel temperatures, and have determined the magnitude and the direction of the internal field at the chlorine nucleus relative to the principal axes of the electric field gradient. © 1969 The American Physical Society.