Angular-dependent planar metamagnetism in the hexagonal compounds TbPtIn and TmAgGe

Detailed magnetization measurements M(T,H,θ), were performed on single crystals of TbPtIn and TmAgGe (both members of the hexagonal Fe₂P∕ZrNiAl structure type) for the magnetic field H applied perpendicular to the crystallographic c axis. These data allowed us to identify, for each compound, the easy axes for the magnetization, which coincided with high symmetry directions ([120] for TbPtIn and [110] for TmAgGe). For fixed orientations of the field along each of the two sixfold symmetry axes, a number of magnetically ordered phases is being revealed by M(H,T) measurements below T_N. Moreover, T≃2 K, ∣M(H)∣_θ measurements for both compounds (with H applied parallel to the basal plane), as well as T=20 K data for TbPtIn, reveal five metamagnetic transitions with simple angular dependencies H_ci,j∼1∕cos(θ±φ), where φ=0° or 60°. The high-field magnetization state varies with θ as 2∕3μ_sat(R³⁺)cos θ, and corresponds to a crystal field limited saturated paramagnetic state. Analysis of these data allowed us to model the angular dependence of the locally saturated magnetizations M_sat and critical fields H_c with a three coplanar Ising-like model, in which the magnetic moments are assumed to be parallel to three adjacent easy axes. Furthermore, net distributions of moments were inferred based on the measured data and the proposed model.