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Neutron investigation of ferrimagnetic compounds containing gadolinium and boron gets easier

Could neutron diffraction be used to determine the magnetic structure of Gd-Co-B compounds ?

It is usually considered impossible (or at best, impractical) to perform neutron diffraction on compounds containing Gd and B due to the extreme thermal neutron absorption cross sections of these elements (natural Gd is the most powerful neutron absorber in the Periodic Table). We show that it is in fact possible to determine the ferrimagnetic structure of the GdCo12-xFexB6 series of compounds which are highly absorbing magnetic materials using a dedicated flat-plate, thin-film set-up.

Transition metal (TM) rich intermetallic compounds are of significant interest as they offer a relatively large magnetization combined with a high magnetic ordering temperature. Since the discovery of the high performance, hard magnetic system based on the Nd2Fe14B phase, extensive investigations have focused on intermetallic ternary borides combining the magnetic properties of a rare-earth with Co or Fe as the TM element. Gd-containing intermetallic compounds are interesting because Gd has a spherical 4f electronic shell (half-full, S-state 4f7) so no contribution to the magnetocrystalline anisotropy is expected from the Gd ions. Gd-Co-B phases are therefore ideal systems to probe the intrinsic magnetic properties of the transition metal sublattice. However, it is usually considered impossible (or at best, impractical) to perform neutron diffraction on compounds containing Gd and B due to the extreme thermal neutron absorption cross sections of these elements (natural Gd is the most powerful neutron absorber in the Periodic Table).

In J. Phys. : Condens. Matter 25 316001, we show that it is in fact possible to determine the ferrimagnetic structure of the GdCo12-xFexB6 series of compounds and to follow its composition dependence in detail. Using a variety of experimental techniques including magnetometry, 155Gd Mössbauer spectroscopy and neutron powder diffraction, we have shown that the orientation direction of the Gd and TM magnetic moments is extremely sensitive to the level of Fe for Co substitution in the GdCo12-xFexB6 series. Indeed, an axial to basal-plane spin-reorientation occurs at very low Fe concentrations x < 0.1. This has been directly confirmed by neutron diffraction experiments performed on these highly absorbing magnetic materials using a dedicated flat-plate, thin-film set-up.

The work is a combined structural, magnetic and spectroscopic study by the Institut Néel of the CNRS and Université Joseph Fourier, Grenoble, France, together with the Physics Department and Centre for the Physics of Materials, McGill University, Montreal, Canada and the School of Physical, Environmental and Mathematical Sciences, UNSW Canberra, Australia. The Grenoble group has extensive expertise in studying the magnetism of intermetallic compounds, neutron scattering and high magnetic field measurements and has investigated numerous compounds with these tools.

Rietveld refinement of the neutron diffraction pattern of GdCo12B6 a highly absorbing compound Rietveld refinement of the neutron diffraction pattern of GdCo12B6 a highly absorbing compound

This work is part of the Ph D Thesis of L.V.B. Diop under the supervision of O. Isnard

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