The growth of single crystals of FeCl₃, through sublimation and from the melt, is presented alongside a thorough investigation of their magnetostructural properties through a combination of DC magnetization and AC magnetic susceptibility measurements, single crystal X-ray diffraction (SCXRD), neutron powder diffraction (NPD) and small-angle neutron scattering (SANS). A new chiral polymorph of FeCl₃ is identified, crystallizing in the non-centrosymmetric space group P3₁. NPD and SANS reveal that a weakly first-order magnetic phase transition occurs from a paramagnetic phase with significant short-range correlations to an antiferromagnetic phase at T_N = 8.6 K, best described by the magnetic propagation vector k = (1/2, 0, 1/3) which differs from the previously reported magnetic structure of the well-known centrosymmetric polymorph (space group R3̄). We show that disordered crystallographic models including a large number of stacking faults are required to accurately reproduce the scattering observed in NPD patterns, preventing full determination of the magnetic structure. The magnetic field and temperature-dependent behavior of the intensities of the k = (1/2, 0, 2/3) and (1/2, 0, 5/3) magnetic Bragg peaks measured by SANS suggest that a field-induced spin reorientation occurs at H = 40 kOe when H‖c-axis and at a significantly lower field of H ≈ 25 kOe when H⊥c-axis. Above these magnetic fields in both cases the spins lie predominantly in the basal plane. The long-range magnetic ordering and the field-induced transitions observed in the neutron scattering experiments coincide with anomalies observed in the magnetisation versus both temperature and applied field along the principal crystal directions.

The bulk helimagnet Cu2OSeO3 represents a unique example in the family of B20 cubic helimagnets exhibiting a tilted spiral and skyrmion phase at low temperatures when the magnetic field is applied along the easy (001) crystallographic direction. Here we present a systematic study of the stability and ordering of these low-temperature magnetic states. We focus our attention on the temperature and field dependencies of the tilted spiral state that we observe persisting up to above T=35 K, i.e., up to higher temperatures than reported so far. We discuss these results in the frame of the phenomenological theory introduced by Dzyaloshinskii in an attempt to reach a quantitative description of the experimental findings. We find that the anisotropy constants, which are the drivers behind the observed behavior, exhibit a pronounced temperature dependence. This explains the differences in the behavior observed at high temperatures (above T=18 K), where the cubic anisotropy is weak, and at low temperatures (below T=18 K), where a strong cubic anisotropy induces an abrupt appearance of the tilted spirals out of the conical state and enhances the stability of skyrmions.