Magnetic properties of RCuAl3 (R = Pr and Nd) compounds

Abstract Magnetic properties of PrCuAl 3 and NdCuAl 3 single crystals, adopting the tetragonal BaNiSn 3 -structure-type, are reported. Our magnetization and specific heat measurements revealed no magnetic ordering in PrCuAl 3 , while NdCuAl 3 orders antiferromagnetically below T N  = 2.45 K. The paramagnetic regime was investigated for both analogues revealing (i) the a-axis as the easy direction of magnetization with (ii) a relatively high uniaxial anisotropy energy of 13.2 meV for PrCuAl 3 compared to a smaller value of 4.7 meV for NdCuAl 3 . The measured data are well explained by rare-earth ground state multiplet splitting in crystal electric field. A powder neutron diffraction experiment confirmed PrCuAl 3 to remain paramagnetic down to 1.5 K. On the other hand, NdCuAl 3 orders antiferromagnetically below T N with an incommensurate magnetic structure described by two propagation vectors k 1  = (1/3 - δ 1 , 0, 0) and k 2  = (1/7 - δ 2 , 1/7 - δ 2 , 0), where δ 1  = 0.035(1) and δ 2  = 0.007(1). The magnetic moments (of both magnetic modulations) are arranged within the basal plane with a small z-component moment allowed by the symmetry. Our results are discussed with respect to other R CuAl 3 compounds.