High magnetic field study of the Tm₂Fe₁₇ and Tm₂Fe₁₇D_3.2 compounds

A magnetization study of a Tm₂Fe₁₇ single crystal and aligned powder of the deuteride Tm₂Fe₁₇D_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. Tm₂Fe₁₇ 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 Tm₂Fe₁₇ 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 Tm₂Fe₁₇, 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 A₆₆ is found from the widths of the steps: A₆₆(b) = −35 Ka ₀ ⁻⁶ and A₆₆(d) = −26 Ka ₀ ⁻⁶ (here a ₀ is the Bohr radius). It also proves possible to estimate the other sixth-order crystal field parameter: A₆₀ ∼ −4 Ka ₀ ⁻⁶ (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 Tm₂Fe₁₇D_3.2 is found to be 49 T or 9% less than in the parent binary compound.