Crystal Structures and Magnetic Properties of Ca2−xSrxMnO4

We prepared Ruddlesden–Popper-type layered perovskites Ca2−xSrxMnO4 (x=0–2.0 at 0.25 intervals). Their precise crystal structures at room temperature and at 10 K were determined from both the X-ray and the neutron diffraction measurements. The compounds for x=0 and 0.25 have a tetragonal system with the space group I41/acd (No. 142). The compounds for x=0.5–2.0 have a tetragonal system with the space group I4/mmm (No. 139). Magnetic susceptibility measurements have been performed for all the compounds in the temperature range between 5 and 350 K. The temperature-dependent magnetic susceptibilities were measured under zero-field-cooled (ZFC) and field-cooled (FC) conditions at an applied field of 1000 G. A dramatic difference in magnetic susceptibilities between ZFC and FC was observed below the Néel temperatures for Ca2MnO4 and Ca1.75Sr0.25MnO4, which shows the onset of a ferromagnetic moment below these temperatures. This moment is caused by the Dzyaloshinsky–Moriya interaction. Magnetic structures of Ca2–xSrxMnO4 (x=0.0, 0.5, 1.0, and 1.5) solid solutions at 10 K have been determined by the neutron diffraction measurements. The nearest-neighbor Mn4+ ions are coupled antiferromagnetically in the (001) planes and the spins are parallel to the c axis.