Crystal and magnetic structure of CrAs as function of temperature and pressure

Chromium arsenide, CrAs (space group Pnma at ambient conditions), is considered a model system in which superconductivity and helimagnetism coexist. The superconductivity is induced by pressure and forms a dome-like phase region with a maximum TC of 2.2 K at about 1 GPa. The superconductivity occurs in the vicinity of an antiferromagnetical phase of CrAs. We investigated the crystal structure of CrAs using synchrotron X-ray single crystal diffraction in dependence of temperature (30–400 K) and on pressure increase (0–9.46 GPa) [1]. The isosymmetrical magnetostructural phase transition at TN ≈ 270 K induces a change in the microstructure by twinning due to a crossing of the orthohexagonal setting of the unit-cell parameter ratio c/b. Within the crystal structure, one particular Cr–Cr distance exhibits an anomalous behavior in that it is nearly unaffected by temperature and pressure in the paramagnetic phase, which is stable above 267 K and at high pressures. The distinct behavior of this shortest Cr–Cr distance might be of importance for the superconducting properties of CrAs.