Incommensurate magnet iron monophosphide FeP: Crystal growth and characterization

We report an optimized chemical vapor transport method that enables the growth of FeP single crystals up to 500 mg in mass and $80{\mathrm{mm}}^3$ in volume. The high quality of the crystals obtained by this method was confirmed by means of energy-dispersive x-ray spectroscopy, high-resolution transmission electron microscopy, low-temperature single-crystal x-ray diffraction, and neutron diffraction experiments. We investigated the transport and magnetic properties of the single crystals, and we calculated the electronic structure of FeP. We show both theoretically and experimentally that the ground state of FeP is metallic. The examination of the magnetic data reveals antiferromagnetic order below $T_{\mathrm{N}}=119\mathrm{K}$ while transport remains metallic in both the paramagnetic and the antiferromagnetic phase. The analysis of the neutron diffraction data shows an incommensurate magnetic structure with the propagation vector $\mathbf{Q}=\left(0,0,\pm \delta \right)$, where δ is close to 0.2. For a full understanding of the magnetic state, further experiments are needed. The successful growth of large high-quality single crystals paves the way for further investigations of itinerant magnets with incommensurate spin structures using a wide range of experimental tools.

Figure 1

Examples of FeP single crystals grown by the iodide vapor transport method. (a) This crystal $(m=519\mathrm{mg})$ was used for inelastic neutron scattering experiments; (b,c) the heaviest crystals from other ICVT experiments (407 and 346 mg, respectively). Cell scale is 1 mm.

Figure 2

EDX spectrum of a FeP single crystal.

Figure 3

X-ray Laue diffraction pattern of FeP crystal [see Fig. 1], measured along the $a$ and $b$ axes.

Figure 4

High-resolution transmission electron microscopy (HRTEM) of FeP. (a) HRTEM image recorded in [001]-orientation. (b) Fourier transform (diffractogram) computed from the HRTEM image (a). (c) Atomic structure model (Fe, gold; P, violet).

Figure 5

Magnetic and transport properties of single-crystal FeP. (a) The temperature dependence of the magnetic susceptibility of FeP; (b) the temperature dependence of the resistivity shows a kink at around 120 K, which is seen more clearly in its temperature derivative (right axis).

Figure 6

Neutron diffraction intensity maps in the $\left(h0l\right)$ plane, measured at $T=10\mathrm{K}$ (left) and $T=200\mathrm{K}$ (right). In the low-temperature dataset, incommensurate magnetic satellites are seen around the (101), (002), (202) and equivalent Bragg reflections. The two powder rings originate from scattering on the sample holder made of polycrystalline aluminum.

Figure 7

X-ray diffraction intensity map in the $\left(hk0\right)$ plane, measured at $T=300\mathrm{K}$. The Bragg peaks violating the extinction rules for the space group Pnma are marked with red circles.

Figure 8

Total and partial density of states for each atomic species of FeP. The Fermi level is set to 0 eV.

Figure 9

(a) Orbital projected representation of the electronic band structure of FeP. The size of the circles is proportional to the weight of $3d{t}_{2g}$ and $e_g$ states of Fe and $3p$ states of P in the corresponding Bloch wave function. (b) Fermi surface in the nonmagnetic state.