Helical magnetic structure and hyperfine interactions in FeP studied by 57Fe Mossbauer spectroscopy and 31P NMR

We report results of Fe-57 Mossbauer and P-31 NMR studies of a phosphide FeP powder sample performed in a wide temperature range including the point (T-N approximate to 120 K) of magnetic phase transitions. The Fe-57 Mossbauer spectra at low temperatures T < T-N present a very complex Zeeman pattern with line broadenings and sizeable spectral asymmetry. It was shown that the change of the observed spectral shape is consistent with the transition into a space-modulated helicoidal magnetic structure. Analysis of the experimental spectra was carried out assuming an anisotropy of the magnetic hyperfine field H-hf at the Fe-57 nuclei when the Fe3+ magnetic moment rotates with respect to the principal axis of the electric field gradient (EFG) tensor. The obtained large temperature independent anharmonicity parameter m approximate to 0.96 of the helicoidal spin structure results from easy-axis anisotropy in the plane of the iron spin rotation. It was assumed that a very low maximal value of H-hf(11 K) approximate to 36 kOe and its high anisotropy Delta H-anis(11 K) approximate to 30 kOe can be attributed to the stabilization of iron cations in the low-spin state (S-Fe = 1/2). The 31P NMR measurements demonstrate an extremely broad linewidth reflecting the spatial distribution of the transferred internal magnetic fields of the Fe3+ ions onto P sites in the magnetically ordered state. (C) 2016 Elsevier B.V. All rights reserved.