Origin of the metamagnetic transitions in Y1−Er Fe2(H,D)4.2 compounds

Abstract

The structural and magnetic properties of Y1-xErxFe2 intermetallic compounds and their hydrides and deuterides Y1-xErxFe2H(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 TFM-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 Btrans1  8 T, related to the change of the Er moments orientation from antiparallel to parallel Fe moment, is observed. Btrans1 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 Btrans2 increases linearly versus temperature and relates to the itinerant electron metamagnetic behavior of the Fe sublattice. An onset temperature TM0 is obtained by extrapolating TFM-AFM (B) at zero field. TM0 decreases linearly versus the Er content and is 45±5 K higher for the hydrides compared to the corresponding deuteride. The evolution of TM0 versus cell volume shows that it cannot be attributed exclusively to a pure volume effect and that electronic effects should also be considered.

Phase diagram and order-disorder transitions in Y0.9Gd0.1Fe2Hx hydrides (x ≥ 2.9)

“…YFe2Hx hydrides were also studied for their magnetic and magnetocaloric properties especially around 4.2 H/f.u., where a ferromagnetic-antiferromagnetic (FM-AFM) transition with an itinerant electron metamagnetic (IEM) character has been observed [20,21,28,29]. This magnetic transition is accompanied by a cell volume variation and is sensitive to any cell volume change induced by an applied external pressure [30,31], D for H isotopic substitution [32,33] or R for Y substitution [34][35][36][37]. For example, the investigation of the monoclinic Y0.9Gd0.1Fe2(H1-zDz)4.2 compounds indicated that upon H for D substitution the FM-AFM transition temperature is shifted to higher temperature, whereas TO-D is shifted to lower value [38].…”

Magnetic and Magnetocaloric Effect of Laves Phase Compounds Er(Fe0.8−xMn0.2−yCox+y)2 with x, y = 0.0 or 0.1

“…One more, such behavior supports the interest of more systematic magnetic characterizations of the RTM 2 series of Laves type compounds, with R being a heavy rare earth metal and TM being a solution of magnetic 3d metals. Otherwise, a structure spacer, such as inserted hydrogen atoms, might be of interest to modify i.e., the DOS in the vicinity of E F and then the magnetic couplings and configurations, as already mentioned here above [29,35,[44][45][46]67].…”

“…should be considered to detail the magnetic properties of the Er(Fe 1−x (Co-Mn) x ) 2 series. However, the concluding statements found in [67], as well as several refs herein mentioned, are of interest, since focusing on a meta-magnetic process is related to an itinerant electron meta-magnetic behavior of the Fe(TM) sublattice and corresponding to peculiarities (or changes) of DOS at the Fe Fermi level.…”

“…In fact, a non-collinear magnetic ordering, depending on the hydrogen content, has yet been proposed by using the latter technique to characterize the magnetic structure in the ErFe 2 -H system [66]. Besides, and very recently, meta-magnetic transitions were pointed out in the derivate parent system Y 1−x Er x Fe 2 (H,D) 4.2 involving inversion from AFM to FM couplings in between Er and Fe lattices [67]. However, for these large hydrogen content, the cubic symmetry of the C15 crystal structure is lowered to a monoclinic space group (C2/m, even better Pc), due to a specific ordering on the tetrahedral site occupancy by H(D).…”

Magnetic, structural and magnetocaloric properties of Y0.9Gd0.1Fe2Hx hydrides

“…A value of magnetic entropy variation (ΔSM) close to that of Gd has been observed in monoclinic YFe2D4.2 and YFe2H4.2 around TFM-AFM = 84 K and 131 K respectively due to the itinerant electron metamagnetic (IEM) behavior of the Fe sublattice [28]. TFM-AFM is highly sensitive to any volume change induced by applying an external pressure [29], H for D isotope substitution [30] or chemical substitution of Y by another rare earth element (R = Gd, Tb, Er) [31][32][33][34]. To observe an MCE effect close to room temperature, we have undertaken a more systematic study of the influence of the chemical substitution for hydrides and deuterides with concentration near 4.2 H(D)/f.u..…”