Magnetic behavior of RRh₃B₂ (R = La to Gd) ternary borides

Abstract

Magnetization of the rare earth ternary borides RRh₃B₂ (R = La to Gd), which crystallize in the hexagonal CeCo₃B₂ type structure, has been measured in the temperature range 4.2 to 300 K. The Curie temperatures have been determined from the low field ac susceptibility measurements. All except LaRh₃B₂ order magnetically. The Gd and Nd compounds have Curie temperatures (T_c) of 91 K and < 20 K, respectively; the effective paramagnetic moments are slightly larger than the corresponding free ion values for trivalent rare earths. The Ce, Sm and Eu compounds show unusual behavior. From unit cell volume considerations, Eu is trivalent (ground state 4f⁶; ⁷F₀) and cerium has a valence greater than 3. In spite of this, CeRh₃B₂ and EuRh₃B₂ exhibit magnetic ordering with T_c's of 108 and 40 K and saturation moments of 0.38 and 0.55μ_B at 4.2 K, respectively. The magnetism in these two compounds is presumed to be of the itinerant type. The compound SmRh₃B₂ has a very small moment at 4.2 K in 20 kOe field (0.046μ_B) and exhibits a peculiar temperature dependence of magnetization.