Abstract
We present a comprehensive investigation of lattice dynamics in the double-helix antiferromagnet FeP by means of high-resolution time-of-flight neutron spectroscopy and ab-initio calculations. Phonons can hybridize with the magnetic excitations in noncollinear magnets to significantly influence their properties. We observed a rich spectrum of phonon excitations, which extends up to $\sim$50 meV. We performed detailed analysis of the observed and calculated spectra for all high-symmetry points and high-symmetry directions of the Brillouin zone. We show that the DFT calculations quantitatively capture the essential features of the observed phonons, including both dispersions and scattering intensities. By making use of the detailed intensity comparison between the theory and the data, we were able to identify displacement vectors for the majority of the observed modes. The overall excellent agreement between the DFT predictions and the experimental results breaks down for the lowest mode at the $Y$-point, whose energy is lower than calculated by $\sim$13%. The present study provides vital information on the lattice dynamics in FeP and demonstrates applicability of the DFT to novel pressure-induced phenomena in related materials, such as MnP and CrAs.
Highlights
Transition-metal monophosphates AP (A = Fe, Mn) are metallic binary compounds that attracted significant attention due to their magnetic and electronic properties
We present a comprehensive investigation of lattice dynamics in the double-helix antiferromagnet FeP by means of high-resolution time-of-flight neutron spectroscopy and ab initio calculations
In the previous section we have shown that our calculations quantitatively reproduce the dispersion and intensity distribution of the observed phonon spectrum at all high-symmetry points of the Brillouin zone (BZ)
Summary
The magnetoresistance appears to be highly anisotropic and shows a linear behavior when the magnetic field is aligned along the c axis, this is along the propagation vector of the helical magnetic structure It was argued [36] that the large nonsaturating magnetoresistance might arise due to the presence of a semi-Dirac point in its electronic structure, which is a feature of the nonsymmorphic symmetry of this material class [14]. The linear magnetoresistance can be linked to the magnetic order, which provides the first evidence on the coupling of different subsystems, electronic and magnetic, in FeP This motivates further studies of this compound, including its lattice dynamics and the relation between its structural, electronic, and magnetic degrees of freedom.
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