Magnetic Properties of Protactinium Tetrachloride

Magnetic susceptibility of PaCl4 was measured from 3.2–296°K with a vibrating-sample magnetometer at fields up to 12 000 Oe. PaCl4 has a ferromagnetic transition at Tc=182±2° K. Below Tc the magnetization deviates markedly from Brillouin behavior and is far from saturation at 12 kOe; hysteresis is absent above 3.3°K. A high degree of covalency is suggested to explain the high Curie point; a large anisotropy energy is indicated by the lack of saturation. From 180–210°K, PaCl4 obeys the Curie—Weiss law, χ=C/(T-θ), with θ=157°K and μ eff=1.04 μ B. The measured paramagnetic properties were compared to those calculated from crystal-field theory, with and without J mixing included. The comparison indicates that J mixing is significant in PaCl4.