Magnetism of rare-earth salts R(CF3SO3)3⋅ 9H2O with R=Tb, Dy, and Ce

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Abstract
Magnetic susceptibilities have been measured between 0.05 and 20 K for three rare‐earth trifluoromethanesulfonate nonahydrates R(CF3SO3)3⋅ 9H2O or RTFMS whose hexagonal crystal structure is very similar to that of the rare‐earth ethylsulfate nonahydrates R(C2H5SO4)3⋅ 9H2O or RES. TbTFMS and DyTFMS order ferromagnetically at TC=0.240 K and TC=0.111 K, respectively. CeTFMS remains paramagnetic down to 0.089 K. All three compounds show extreme Ising‐type anisotropy with g⊥∼0. g∥ of each RTFMS compound compares favorably with that of the corresponding RES as expected from crystalline field theories based on a point‐charge model. In each case, the Weiss constant is close to what is expected for a system with predominantly dipolar interactions. The ferromagnetic ordering in TbTFMS and DyTFMS is essentially that of a dipolar Ising system. The splitting Δ of the ground quasi‐doublet in TbTFMS is only ∼0.5 K and the ordering appears to be largely explained by electronic models although substantial ordering of nuclear spins is indicated in our preliminary heat capacity data.