Specific features of the magnetic properties of RB4 (R = Ce, Sm and Yb) tetraborides. Effects of pressure

The temperature dependence and the effect of pressure P up to 2 kbar on the magnetic susceptibility chi of the tetraborides SmB4 and YbB4 was studied. For the compound CeB4, the electronic structure and magnetic susceptibility were calculated from first principles as a function of the atomic volume. The results show that in the studied tetraborides, rare-earth ions (Ce4+, Sm3+ and Yb2.8+) exhibit different valence states, which determines the specific features of their magnetic properties. In particular, the obtained pressure derivatives of susceptibility dln chi/dP for cerium, samarium and ytterbium tetraborides are -2, -0.6 and +2.7 (in units of Mbar(-1)), respectively, which are characteristic for the exchange-enhanced itinerant paramagnetism, Van Vleck ionic paramagnetism with a stable f-shell, and the magnetism of rare-earth ions in the intermediate valence state. (C) 2015 AIP Publishing LLC.