NMR study of magnetic structure and hyperfine interactions in binary helimagnet FeP

TL;DR

This study uses ${}^{31}$P NMR spectroscopy to analyze the magnetic structure and hyperfine interactions in FeP, revealing an incommensurate helimagnetic ground state and a field-induced spin-reorientation transition.

Contribution

It provides a detailed NMR-based model of FeP's magnetic structure, including spin reorientation effects, aligning with neutron scattering data and offering new insights into hyperfine interactions.

Findings

Identification of incommensurate helimagnetic ground state.

Observation of a field-induced spin-reorientation transition.

Development of an effective NMR-based magnetic structure model.

Abstract

We report a detailed study of the ground state helical magnetic structure in monophosphide FeP by means of ${}^{31}$P 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 ${}^{31}$P 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 ${}^{31}$P 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 ${}^{31}$P 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$^{\circ}$ and 176$^{\circ}$ between Fe1-Fe3 (Fe2-Fe4) and Fe1-Fe2 (Fe3-Fe4) sites, respectively, in accordance with the neutron scattering data.