Magnetization measurements along the main symmetry directions of the tetragonal structure, [100], [110] and [001], have been performed on several single crystals (R = Y, Tb and Ho), at applied high magnetic fields up to 12 Tesla and temperatures ranging from 4.2 to 300 K. From the measurements on the yttrium compound the second- and fourth-order anisotropy constants and the spontaneous magnetization of the Fe sublattice have been determined. The complex magnetic behaviour has been explained using a single-ion model for the crystal electric field (CEF) interaction and a mean-field model for the exchange interaction. A reliable set of CEF parameters and mean exchange field have been obtained for the and intermetallic compounds. All the experimental features observed, the first-order magnetization process under magnetic field in and spin reorientation transition (SRT) in , have been explained using such CEF and exchange parameters. A study of the character of the SRT observed in the intermetallic compound has been undertaken by measuring the parallel and perpendicular components of the magnetization to the applied magnetic field. The experimental results obtained have been explained considering the coexistence of two magnetic phases for temperatures close to the spin reorientation one.

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A magnetization study of a Tm 2 Fe 17 single crystal and aligned powder of the deuteride Tm 2 Fe 17 D 3.2 has been carried out in steady (14 T) and pulsed (60 T and, in one case, up to 74 T) magnetic fields at temperatures between 1.5 and 300 K. Tm 2 Fe 17 is a ferrimagnet with T C = 295 K and a spontaneous moment of 22 μ B /f.u. at T = 4.2 K. Of particular interest are low-temperature magnetization curves along the sixfold crystal axis c, which is an easy direction in Tm 2 Fe 17 and a hard direction in the deuteride. In either case the magnetization increases with magnetic field undulatorily in broad steps whose height is a multiple of the atomic moment of Tm, μ Tm = 7 μ B . In Tm 2 Fe 17 , the positions of the steps yield information on the Fe-Tm molecular field, 48 T on the Tm 2d site and 60 T on the Tm 2b site, whereas the crystal field parameter A 66 is found from the widths of the steps: A 66 (b) = −35 Ka −6 0 and A 66 (d) = −26 Ka −6 0 (here a 0 is the Bohr radius). It also proves possible to estimate the other sixth-order crystal field parameter: A 60 ∼ − 4 Ka −6 0 (on average for both sites). Less information can be extracted from the powder data for the deuteride. Thus, the mean molecular field on Tm in Tm 2 Fe 17 D 3.2 is found to be 49 T or 9% less than in the parent binary compound.

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