Origin of the metamagnetic transitions in Y1-xErxFe2(H,D)4.2 compounds

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 , whereas corresponding hydrides and deuterides crystallize in a monoclinic structure. 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.Comment: 22 pages, 10 figure

Local deuterium order in apparently disordered Laves phase deuteride YFe₂D_4.2

Deuterium short-range order in cubic Laves phase deuteride YFe2D4.2 was studied by neutron (ToF) powder diffraction experiments and Pair Distribution Function (PDF) analysis between 290 and 400 K. The minimal allowed D–D distance of 2.1 Å in a metal deuteride (Switendick rule) has been experimentally proved in the HT-disordered phase YFe2D4.2. It has been found that the distribution of deuterium atoms around the iron is not random, and cannot be explained only by applying the Switendick rule. The first coordination sphere of iron atoms in the high temperature (HT)-disordered phase resembles between 350 and 400 K the coordination observed in the low temperature (LT)-ordered phase. Reversed Monte Carlo modeling of the Pair Distribution Function of the HT-disordered phase prefers the coordination FeD5 and FeD4 in agreement with the LT-ordered phase

Metamagnetic transitions in Y0.5Er0.5Fe2D4.2 deuteride studied by high magnetic field and neutron diffraction experiments

International audienceThe structural and magnetic properties of Y 0.5 Er 0.5 Fe 2 D 4.2 deuteride have been investigated by continuous high field magnetic measurements up to 35 T and neutron powder diffraction experiments versus temperature and applied field. Y 0.5 Er 0.5 Fe 2 D 4.2 crystallizes in a monoclinic structure (Pc space group) resulting from the deu-terium order into 18 interstitial tetrahedral sites. At low field, the deuteride is ferrimagnetic (Ferri) up to 38 K, between 38 and 50 K, it undergoes a first order transition towards an antiferromagnetic (AFM) structure, which remains present up to T N = 115 K. Upon applied field, two different types of metamagnetic behavior are observed depending on the temperature range. Below 38 K, a forced ferrimagnetic-ferromagnetic (FM) transition is observed at a transition field B Trans of only 7 T (at 2 K), which is among the smallest encountered for Fe rich intermetallics. B Trans is not very sensitive to temperature changes nor to the Er content and its moderate value is explained by a deuterium induced weakening of the Er-Fe interaction. The second metamagnetic transition, observed between 38 and 150 K, from an AFM (Para) towards a FM structure, is related to the itinerant electron metamagnetic behavior of the Fe sublattice. B Trans increases linearly versus temperature with a dB/dT slope of 0.24 ± 0.01 T.K −1. Above B Trans , Er moments parallel to the Fe moments are induced

High field induced magnetic transitions in the Y 0.7 E r 0.3 F e 2 D 4.2 deuteride

International audienc

Homogeneity Range and Order-Disorder Transitions in R1-xNi2 Laves Phase Compounds

The range of homogeneity has been studied in R1-xNi2 Laves phases (R=Ce, Gd, Tb) by x ray diffraction, microprobe analysis and density measurements. In these compounds the number of R vacancies varies as a function of the nature of the rare earth and the nominal composition. For R=Tb the number of vacancies varies by 0 £ x £ 0.5, from a pure C15 structure to a 2a superstructure accompanied by a cell volume decrease. The order-disorder transition of the rare earth vacancies has been studied under applied pressure for La7Ni16 and versus temperature for all the -xNi2 compounds. The evolution of the pressure and temperature transition, which reflects the binding energy of the vacancies, depends not only on the radius of the R element but also on the mass of the R atom.JRC.E.6-Actinides researc

Deuterium ordering in Laves-phase deuteride YFe₂D_4.2

The structure of Laves-phase deuteride YFe2D4.2 has been investigated by synchrotron and neutron (ToF) powder diffraction experiments between 60 and 370 K. Below 323 K, YFe2D4.2 crystallizes in a fully ordered, monoclinic structure (s.g. Pc, Z=8, a=5.50663(4), b=11.4823(1), c=9.42919(6) Å, β=122.3314(5)°, V=503.765(3) Å3 at 290 K) containing 4 yttrium, 8 iron and 18 deuterium atoms. Most D–D distances are, within the precision of the diffraction experiment, longer than 2.1 Å; the shortest ones are of 1.96 Å. Seven of eight iron atoms are coordinated by deuterium in a trigonal bipyramid, similar to that in TiFeD1.95−2. The eighth iron atom is coordinated by deuterium in a tetrahedral configuration. The coordination of iron by deuterium, and the iron-deuterium distances point to the importance of the directional bonding between iron and deuterium atoms. The lowering of crystal symmetry due to deuterium ordering occurs at much higher temperature than the magnetic ordering, and is therefore one of the parameters that are at the origin of the magnetic transition at lower temperatures