Low-temperature structural anomalies in Pr$_{0.5}$Sr$_{0.5}$CoO$_{3}$

The magnetic and crystal structures of the Pr$_{0.5}$Sr$_{0.5}$CoO$_{3}$ metallic ferromagnet have been studied by the neutron diffraction technique. It is demonstrated that below $150$ K, the compound is mesoscopically separated into two crystalline phases with different spatial symmetries and with different directions of the magnetic anisotropy. The phase separation exists down to $1.5$ K, and at temperatures below $90$ K, the low-symmetry phase occupies about 80% of the sample volume. The main structural difference between the phases is the configuration of oxygen atoms around praseodymium and, to a certain extent, around cobalt. The ferromagnetic structure with the magnetic moment lying in the basal plane of the structure ($\mu_{\rm Co}\approx 1.7 \,\mu_{B }$ at $1.5$ K) arises at $234$ K, whereas the component directed along the long axis of the unit cell appears at $130$ K. The formation of the new structural phase and change in the orientation of the magnetic moment give rise to the anomalies of the physical and magnetic characteristics of this compound observed earlier at temperatures about $120$ K.