Magnetic Properties of Thulium Metal

Measurements made from 1.3 to 300°K, in field up to 12 000 oe, show that thulium becomes antiferromagnetic on cooling to 60°K and is ferromagnetic below 22°K. In agreement with earlier work the susceptibility between 70 and 300°K obeys the Curie-Weiss law and the effective Bohr magneton number is 7.6, equal to the theoretical value for the trivalent ion core having two holes in the $4f$ shell. The highest observed ferromagnetic moment is only 0.5 Bohr magneton whereas the theoretical value is $gJ=7\mathrm{}$. Large hysteresis and crystal anisotropy are observed at the lowest temperatures. It is suggested that the anisotropy is so large that the magnetization cannot be deviated appreciably from the hexagonal axis even in the higher fields (70 000 oe) used by Henry; he observed 3.4 Bohr magnetons whereas the highest expected for polycrystalline material on this assumption is 3.5.