Ru M 3 -edge resonant inelastic x-ray scattering (RIXS) measurements of α-RuCl 3 with 27 meV resolution reveals a spin-orbit exciton without noticeable splitting. We extract values for the spin-orbit coupling constant (λ = 154 ± 2 meV) and trigonal distortion field energy (|∆| < 65 meV) which support the j eff = 1/2 nature of α-RuCl 3 . We demonstrate the feasibility of Medge RIXS for 4d systems, which allows ultra high-resolution RIXS of 4d systems until instrumentation for L-edge RIXS improves.

Using x-ray emission spectroscopy, we find appreciable local magnetic moments until 30-40 GPa in the high-pressure phase of iron, however no magnetic order is detected with neutron powder diffraction down to 1.8 K contrary to previous predictions. Our first-principles calculations reveal a "spinsmectic" state lower in energy than previous results. This state forms antiferromagnetic bilayers separated by null spin bilayers, which allows a complete relaxation of the inherent frustration of antiferromagnetism on a hexagonal close-packed lattice. The magnetic bilayers are likely orientationally disordered, owing to the soft interlayer excitations and the neardegeneracy with other smectic phases. This possible lack of long-range correlation agrees with the null results from neutron powder diffraction. An orientationally-disordered, spinsmectic state resolves previously perceived contradictions in high pressure iron and could be integral to explaining its puzzling superconductivity.Iron is well-known since antiquity for its unique magnetic properties and continues to captivate scientists to this day. The study of iron and its alloys has many applications, including steel production and geophysics. Regarding the latter, the application of hydrostatic pressure induces a phase transition from the body-centered cubic (bcc) structure of α-iron to the hexagonal close-packed (hcp) structure of ε-iron (Fig. 1). Iron is being studied at increasingly high pressures and temperatures, since it and its alloys compose the majority of the Earth's core (1). Nonetheless, the relatively low-pressure, low-temperature region of ε-iron has remained a mystery for decades. The ferromagnetism (fm) found in α-iron disappears during the α-ε transition (2-4), however the magnetic state of 1 B.W.L and T.G contributed equally to this work 2 Corresponding author -matteo.dastuto@neel.cnrs.fr -Institut Néel CNRS -25, av des Martyrs -38042 Grenoble cedex 9; tel: (+33)(0)4 76 88 12 84 arXiv:1903.04792v2 [cond-mat.mtrl-sci]

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