Magnetic ordering and effects of crystal electric field anisotropy in the hexagonal compounds RPtIn (R=Y,Gd–Lu)

Single crystals of RPtIn R=Y, Gd–Lu were grown out of In-rich ternary solution. Powder x-ray diffraction data on all of these compounds were consistent with the hexagonal ZrNiAl-type structure (space group P6̅ 2m). The R=Tb and Tm members of the series appear to order antiferromagnetically (T_N=46.0 and 3.0 K, respectively), whereas the R=Gd, Dy–Er compounds have at least a ferromagnetic component of the magnetization along the c axis. The magnetic ordering temperatures of all of these systems seem to scale well with the de Gennes factor, whereas the curious switching from ferromagnetic to antiferromagnetic ordering across the series is correlated with a change in anisotropy, such that, in the low-temperature paramagnetic state, χ_ab>χ_c for the antiferromagnetic compounds and χ_c>χ_ab for the rest. In order to characterize the magnetic ordering across the RPtIn series, a three-dimensional model of the magnetic moments in Fe₂P-type systems was developed, using the three coplanar Ising-like systems model previously introduced for the extremely planar TbPtIn compound: given the orthorhombic point symmetry of the R sites, we assumed the magnetic moments to be confined to six nonplanar easy axes, whose in-plane projections are rotated by 60° with respect to each other. Such a model is consistent with the reduced high-field magnetization values observed for the RPtIn compounds R=Tb–Tm, and qualitatively reproduces the features of the angular dependent magnetization of Ho_xY_1−xPtIn at H=55 kG.