We report a detailed study of the ground state helical magnetic structure in monophosphide FeP by means of 31P NMR spectroscopy. We show that the zero-field NMR spectrum of the polycrystalline sample provides strong evidence of an anisotropic distribution of local magnetic fields at the P site with substantially lower anharmonicity than that found at the Fe site by M\"{o}ssbauer spectroscopy. From field-sweep 31P NMR spectra we conclude that a continuous spin-reorientation transition occurs in an external magnetic field range of 4 - 7 T, which is also confirmed by specific-heat measurements. We observe two pairs of magnetically inequivalent phosphorus positions resulting in a pronounced four-peak structure of the single crystal 31P NMR spectra characteristic of an incommensurate helimagnetic ground state. We revealed a spatial redistribution of local fields at the P sites caused by Fe spin-reorientation transition in high fields and developed an effective approach to account for it. We demonstrate that all observed 31P spectra can be treated within a model of an isotropic helix of Fe magnetic moments in the (ab)-plane with a phase shift of 36∘ and 176∘ between Fe1-Fe3 (Fe2-Fe4) and Fe1-Fe2 (Fe3-Fe4) sites, respectively, in accordance with the neutron scattering data.
@article{arxiv.2008.10975,
title = {NMR study of magnetic structure and hyperfine interactions in binary helimagnet FeP},
author = {A. A. Gippius and A. V. Tkachev and S. V. Zhurenko and N. Büttgen and M. Schädler and I. O. Chernyavskii and I. V. Morozov and S. Aswartham and B. Büchner and A. S. Moskvin},
journal= {arXiv preprint arXiv:2008.10975},
year = {2021}
}