Local magnetic anisotropy by polarized neutron powder diffraction: Application of magnetically induced preferred crystallite orientation

Abstract

Polarized neutron diffraction allows one to determine the local susceptibility tensor on the magnetic site both in single crystals and powders. It is widely used in the studies of single crystals, but it is still hardly applicable to a number of highly interesting powder materials, such as molecular magnets or nanoscale systems because of the low luminosity of existing instruments and the absence of appropriate data analysis software. We show that these difficulties can be overcome by using a large area detector in combination with the two-dimensional Rietveld method and powder samples with a magnetically induced preferred crystallite orientation. This is demonstrated by revisiting two test powder compounds, namely, the low anisotropy (soft) ferrimagnetic compound Fe_{3}O_{4} and the spin-ice compound Ho_{2}Ti_{2}O_{7} with high local anisotropy. The values of the magnetic moments in Fe_{3}O_{4} and the susceptibility tensors of Ho_{2}Ti_{2}O_{7} at various temperatures and fields were found in perfect agreement with these found earlier in single-crystal experiments. The magnetically induced preferred crystallite orientation was used to study the local susceptibility of a single-molecule magnet Co([(CH_{3})_{2}N]_{2}CS)_{2}Cl_{2}. Hence, the studies of local magnetic anisotropy in powder systems might now become accessible.