Origin of the metamagnetic transitions in Y_{1− x}Er_xFe₂(H,D)_4.2 compounds

The structural and magnetic properties of Y_1−xEr_xFe₂ intermetallic compounds and their hydrides and deuterides Y_1−xEr_xFe₂H(D)_4.2 have been investigated using X-ray diffraction and magnetic measurements under static and pulsed magnetic field up to 60 T. The intermetallics crystallize in the C15 cubic structure (Fd-3m space group), whereas corresponding hydrides and deuterides crystallize in a monoclinic structure (Pc space group). All compounds display a linear decrease of the unit cell volume versus Er concentration; the hydrides have a 0.8% larger cell volume compared to the deuterides with same Er content. They are ferrimagnetic at low field and temperature with a compensation point at x=0.33 for the intermetallics and x=0.57 for the hydrides and deuterides. A sharp first order ferromagnetic-antiferromagnetic (FM-AFM) transition is observed upon heating at T_FM−AFM for both hydrides and deuterides. These compounds show two different types of field induced transitions, which have different physical origin. At low temperature (T < 50 K), a forced ferri-ferromagnetic metamagnetic transition with B_trans1 ≈8 T, related to the change of the Er moments orientation from antiparallel to parallel Fe moment, is observed. B_trans1 is not sensitive to Er concentration, temperature and isotope effect. A second metamagnetic transition resulting from antiferromagnetic to ferrimagnetic state is also observed. The transition field B_trans2 increases linearly versus temperature and relates to the itinerant electron metamagnetic behavior of the Fe sublattice. An onset temperature T_M0 is obtained by extrapolating T_FM−AFM (B) at zero field. T_M0 decreases linearly versus the Er content and is 45 ± 5 K higher for the hydrides compared to the corresponding deuteride. The evolution of T_M0 versus cell volume shows that it cannot be attributed exclusively to a pure volume effect and that electronic effects should also be considered.