Magnetic properties of oxides with high concentrations of rare-earth elements R 6 AO12 (R = rare-earth element, A = Mo or W)

We report on the magnetic properties of isostructural oxides R₆AO₁₂ (R = a rare-earth element, A = Mo or W) with high concentrations of rare-earth elements. We measured the magnetization and specific heat. Tm₆MoO₁₂ is a van Vleck paramagnet with a nonmagnetic singlet ground state (GS). Ho₆WO₁₂ exhibits an antiferromagnetic long-range order (AFM LRO) lower than $T_N=2.1$ K and its GS is a magnetic quasi-doublet. Dy₆WO₁₂ shows an AFM LRO lesser than $T_N=2.7$ K and its GS is a magnetic Kramers doublet. Er₆MoO₁₂ and Er₆WO₁₂ are Curie-Weiss paramagnets at temperatures above 2 K and both have a magnetic Kramers doublet GS. We evaluated the magnetic entropy change. The temperature of the maximum magnetic entropy change for a magnetic-field change of 5 T is high (15 K) in Tm₆MoO₁₂ in spite of an oxide containing only rare-earth ions as the magnetic ions.