R. Fruchart

Mossbauer spectroscopy of R2Fe14B

The authors present results obtained by 57Fe Mossbauer spectroscopy on R2Fe14B, where R represents any of the rare earth elements except Pm, Eu and Yb. Additional measurements have been performed on oriented powder for R=Y, Pr and Ho. For the case of Y the measurements at 4.2 K were performed in applied magnetic fields up to 4 T. From these measurements it is deduced that the only compounds with an easy c axis at room temperature which show a spin reorientation of the iron sublattice at a lower temperature are the Nd and Ho alloys. Iron hyperfine fields are anisotropic and the anisotropy has different signs on different sites. An analysis of the non-4f contribution to the electric field gradient at the 161Dy or 166Er nuclei in Dy2Fe14B and Er2Fe14B is consistent with published results on 155Gd in Gd2Fe14B. In order to explain that a spin rotation is found only for R=Nd, Ho the authors invoke the relative small quadrupole moment of the 4f shell for these two ions and crystal field terms of higher than second order.

Magnetization, 57Fe and 161Dy Mössbauer study of Dy2Fe14BHx with 0 ⩽ x ⩽ 4.7

Abstract From the hydrogen dependence of Mossbauer hyperfine parameters in Dy2Fe14BHx and neutron diffraction results on Y2Fe14BD3.5 we infer the hydrogen localization as a function of hydrogen concentration in Dy2Fe14BHx. Our 161Dy Mossbauer spectroscopy data recorded at 4.2 K put constraints on the magnetic properties of the heavy rare-earth (RE) ions in RE2Fe14BHx. A combination of results from 57Fe Mossbauer spectroscopy and bulk magnetization measurements allows us to determine the magnetic structure of the compounds.

Structures magnetiques et transitions du premier ordre dans les perovskites metalliques GaMn3(C1−xNx). Relation avec les composes de terres rares a changement de valence

Abstract Strong analogies are shown between the change of electronic structure in metallic perovskite-type compounds of manganese GaMn 3 (C 1−x N x ) and the valence instabilities in rare earth compounds.

Hydrogen dependence of the intrinsic magnetic properties of R2Fe14B

Abstract Magnetization measurements on Dy2Fe14BHx show that hydrogen increases the magnetization Ms, the Curie temperature Tc and the magneto-crystalline anisotropy. On saturation, at x = 4.7, Ms increased from 9 to 15 μB per formula unit at 4.2 K, Tc increased from 595 to 661 K and the phenomenological fourth-order anisotropy constant K2 was doubled throughout the range 4.2–300 K. A non-collinear spin structure was deduced for the dysprosium sublattices in the hydride. No spin reorientation was observed for Er2Fe14BHx. as x was varied at room temperature.

Transformations de phases dans les nitrures et carbures du manganese de structure-type perovskite

Abstract We have studied, mostly by neutron diffraction, systems derived from Mn 3 GaN: Mn 3 Ga 1-x Mn x N (substitution on the metal) and Mn 3 GaN 1-X C x (substitution on the metalloid). New magnetic structures, different from the end members x = 0 and x = 1 and different in each type of substitution, appear with an appreciable ferromagnetic component. A chemical pressure effect acting on the Mn-octahedron, contracting or expanding the distance Mn-metalloid seems to be responsible for structural and magnetic phase transitions.

Evolution structurale et magnetique des perowskites metalliques (Sn1−xMnx) Mn3C structure magnetique non colineaire de SnMn3C

The non-colinear magnetic structure of the perovskite carbide SnMn3C has been studied by neutron diffraction. A crystallographic and magnetic analysis shows a first order transition to take place in the solid solutions (Sn1−xMnx) Mn3C towards x = 0.1.

Positive muon spectroscopy of Nd2Fe14B and Pr2Fe14B

Abstract We have performed positive muon spin rotation measurements on polycrystalline samples of Nd 2 Fe 14 B and Pr 2 Fe 14 B in zero applied field. In both samples a single sharp μSR line was observed which was unexpected in this complicated structure. The temperature dependence of the muon frequency for Nd 2 Fe 14 B clearly reflects the spin reorientation below 150 K and can be explained qualitatively by assuming that only the c -axis component of a magnetization is sampled by the muon. A smooth decrease of the muon frequency with increasing temperature is observed for Pr 2 Fe 14 B.

Instabilites electroniques dans les composes du manganese de type perovskite metallique. Relation avec les changements de valence dans les composes de terres rares

Abstract Structural instabilities can be systematically induced in metallic perovskites of manganese. Analogies are shown between the instabilities of manganese and the valence changes in rare earth compounds.

Mössbauer spectroscopy on RE2Fe14BHx (RE-Y, Ce, Dy, Er) alloys

RE2Fe14B alloys and some of their hydrides have been studied through57Fe and161Dy Mössbauer spectroscopy (MS). For both the paramagnetic and ordered phases a consistent and physically sound analysis of the57Fe spectra is presented. Fe hyperfine fields and the local magnetic moments are obtained and compared with magnetic and structural data. A spin reorientation is observed for Er2Fe14B. A constant collinear structure down to 4.2 K was determined for the other samples. The161Dy spectra are interpreted for a pure ¦JZ=15/2 > ground multiplet in Dy2Fe14B and its hydride. The B2 crystal field parameters were estimated empirically for the Dy-alloy. Their values can account for the anisotropy in the compounds.

Effets locaux et interactions magnetiques a courte distance dans les perovskites metalliques du manganese mixtes SnMn3CCuMn3N

Abstract The study of the solid solution between the magnetically isotypic compounds SnMn 3 C and CuMn 3 N shows important short range magnetic effects due to the intervention of Mn-N and Mn-C bonds.