Magnetic Properties of Rare Earth Hydroxides

Abstract

The rare‐earth hydroxides, R(OH)₃ with R–La to Yb and Y form a series of simple magnetic crystals isostructural with the hexagonal rare‐earth trichlorides. Compared with most ionic rare‐earth crystals they have relatively small lattice parameters, and one may therefore expect magnetic cooperative effects at readily accessible temperatures. In this paper we report the first series of magnetic measurements on small, hydrothermally grown single crystals (1 to 10 mg) which show that Tb(OH)₃, Dy(OH)₃, and Ho(OH)₃ order ferromagnetically at 3.72°, 3.50°, and 2.55°K, respectively, while Nd(OH)₃ and Gd(OH)₃ undergo more complex antiferromagnetic transitions near 1.7° and 2.0°K. Er(OH)₃ remains paramagnetic down to 1.2°K. Magnetization measurements on Tb(OH)₃, Dy(OH)₃, and Ho(OH)₃ in fields up to 14 kG give saturation moments (corrected for Van Vleck temperature‐independent paramagnetism) of 1350 emu/cc (9.0 μ_B/ion), 1418 emu/cc (9.6 μ_B/ion), and 1121 emu/cc (7.6 μ_B/ion) parallel to the c axis and almost zero perpendicular to the c axis. The correspondingly large and anisotropic magnetic dipole interactions account approximately for the observed Curie temperatures, suggesting that Tb(OH)₃, Dy(OH)₃, and Ho(OH)₃ may be among the simplest examples of Ising‐like systems studied so far, with dominant interactions along linear chains of nearest neighbors. Single crystals are found to be chemically stable with apparently good optical properties, suggesting useful applications to magneto‐optic devices. These are discussed briefly.