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

TL;DR

This paper demonstrates a method using polarized neutron diffraction with a large area detector and magnetically induced preferred crystallite orientation to measure local magnetic anisotropy in powder materials, previously difficult to analyze.

Contribution

It introduces a novel approach combining 2D Rietveld analysis and magnetically induced orientation to study local susceptibility tensors in powders.

Findings

Accurate susceptibility tensors obtained for Fe3O4 and Ho2Ti2O7 consistent with single crystal data.

Method successfully applied to a single-molecule magnet, expanding analysis capabilities.

Overcomes previous limitations of low luminosity and software in powder magnetic anisotropy studies.

Abstract

Polarized neutron diffraction allows 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, like molecular magnets or nanoscale systems because of the low luminosity of existing instruments and the absence of an 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 magnetically induced preferred crystallite orientation. This is demonstrated by revisiting two test powder compounds, namely, low anisotropy (soft) ferrimagnetic compound Fe3O4 and spin-ice compound Ho2Ti2O7 with high local anisotropy. The values of magnetic moments in Fe3O4 and the susceptibility tensors of Ho2Ti2O7 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([(CH3)2N]2CS)2Cl2. Hence, the studies of local magnetic anisotropy in powder systems might now become accessible.