I. Marchuk

Structural and magnetic properties of RFe2H5 hydrides (R=Y, Er)

The structural and magnetic properties of RFe 2 hydrides (R=Y, Er) synthesized under high hydrogen pressures of 10 kbar and 373 K, have been investigated. Both saturated RFe 2 H 5 hydrides absorb about 5 H/f.u. and crystallize in the same type of orthorhombic structure (Imm2 space group), with a=5.437(1) A, b=5.850(1) A and c=8.083(1) A for YFe 2 H 5 and a=5.424(1) A, b=5.793(1) A and c=8.009(1) A for ErFe 2 H 5 . The large hydrogen pressure, necessary to reach 5 H/f.u. can be attributed to a partial filling of all types of available interstitial sites. YFe 2 H 5 displays a weak ferromagnetic behavior, which is almost independent of the temperature. ErFe 2 H 5 shows also a weak magnetization at high temperature whereas below 20 K its magnetization sharply increases due to Er magnetic ordering.

Neutron diffraction study of ZrM2Dx deuterides (M=Fe, Co)

Abstract The structure of ZrFe2 and ZrCo2 deuterides prepared under very high deuterium pressure has been studied by neutron diffraction (ND) at 10 K. The patterns of both compounds are refined with a mixture of intermetallic compound and deuteride. For ZrFe2Dx, the cell volume increases with 23% and the 2.7 D/f.u. are located randomly in A2B2 sites. The Fe moments order in a ferromagnetic structure and increase from 1.8 to 2.2 μB/Fe upon D absorption. The ZrCo2 deuteride shows a doubling of the cell parameter due to deuterium order of 2 D/f.u. in 7 over 12 A2B2 sites with a cell volume increase of 12%.

Structural and magnetic properties of ErFe2D5 studied by neutron diffraction and Mössbauer spectroscopy

A neutron powder diffraction study of ErFe2D5, synthesized under 1 GPa hydrogen pressure, shows that it crystallizes at room temperature in an orthorhombic structure described by the Pmn21 space group with a = 5.42 A, b = 5.79 A, c = 8.00 A. The deuterium atoms order preferentially in some A2 B2 and AB3 interstitial sites. Below 5 K the erbium moments order in a canted magnetic structure, with an erbium moment of 6.6 μB at 1.4 K. The 57Fe Mossbauer spectra of ErFe2D5 from 4.2 to 300 K indicate that there are no ordered Fe moments at zero field. These results are discussed in relation to the influence of hydrogen absorption on the magnetic interactions.

Structural, thermal and magnetic properties of ErMn2D6 synthesized under high deuterium pressure

An ewphase of ErMn2D6 has been prepared by applying high hydrogen pressure on C14 ErMn2 .T hisphase is isostructural to YMn2D6 and crystallizes with a K2PtCl6 type structure havin ga n ordered anion and a partially disordered cation arrangement as Er and half the Mn atoms are randomly substituted in the same 8c site. This hydride is very stable and decomposes into ErD2 and Mn at about 630 K. The reverse susceptibility follows a Curie–Weiss law with an effective moment of 10 µB similar to that of ErMn2 .A lthough a saturation magnetization of 5 µB is measured at 4.2 K, smaller than that of ErMn2 (8 µB), no long range magnetic order is observed in the neutron patterns. Short range magnetic order, corresponding to both ferromagnetic and antiferromagnetic correlations, is observed in the neutron patterns up to 5 K. The chemical disorder of Er and Mn atoms on the 8c site should prevent the long range magnetic order and favour a distribution of Er spin orientation.

Pressure induced phase transitions and EOS of several Laves phase hydrides

Abstract Two C15 Laves phases YFe 2 , ErFe 2 and their hydrides YFe 2 H 5.6 and ErFe 2 H 5.6 were compressed up to 31 GPa by using a diamond anvil cell. Pressure induced phase transitions were found in both YFe 2 H 5.6 and ErFe 2 H 5.6 . Parameters of equation of state were derived for all the phases investigated.

57Fe Mössbauer spectroscopic study for Fe(pyridine)2Ni(CN)4spin-crossover compound

We have measured the 57Fe Mössbauer spectra of the Hofmann pyridine complex Fe(pyridine)2Ni(CN)4 sample before and after exposure to high pressure of gaseous xenon. The temperature dependence of the high spin molar fraction has been determined from the 57Fe Mössbauer spectra. The spin transition of the sample without the high pressure treatment occurs between 175 and 220 K with a hysteresis width of 15 K. Although the 57Fe Mössbauer spectra suggest that the spin crossover behavior of the sample before and after the high pressure treatment are almost the same, the hysteresis of the latter sample is somewhat larger.