Magnetic and electrical properties of K2NiF4-type Sr2CrO4

Sr2CrO4 with a K2NiF4 structure can be synthesized by different methods under ambient pressure and high pressure, while the properties reported are quite different. In this paper, pure phase Sr2CrO4 with K2NiF4 structure is obtained by one-step solid state reaction under high pressure and high temperature. Powders of SrO and CrO2 are used as the starting materials. The Sr2CrO4 structure at room temperature is determined by powder XRD measurement and GSAS Rietveld refinement. Sr2CrO4 crystal is of tetragonal symmetry with space group I4/mmm and its lattice parameters a = 3.8191 Å and c=12.5046 Å. There are two oxygen sites, apical O1 and equatorial O2. The CrO6 octahedron is slightly elongated along the c-axis, forming a longer bond Cr–O1=1.9180 Å and a shorter bond Cr–O2=1.9096 Å. Temperature dependence of the magnetic susceptibility is measured in the temperature range of 2-300 K under the magnetic field 1 T. A weak antiferromagnetic transition can be seen at TN=95 K. Above TN, the susceptibility obeys Curie-Weiss law. The Curie-Weiss fitting gives the Weiss constant θ =-364 K and the effective magnetic moment μeff=2.9 μB, in good agreement with the theoretical value of localized Cr4+, indicating the localized electronic state. Field dependence of susceptibility has been measured at different temperatures. The magnetic properties here are different from those in the previous reports, and this discrepancy is attributed to the quite different sample synthesis methods. Temperature dependence of electrical resistivity of Sr2CrO4 shows insulating behavior. Activation energy Δ is estimated by the relation ρ ∝ exp(Δ/kBT) at temperature range 150-300 K. In the temperature range 150-200 K and 200-300 K the activation energies are ΔL=0.134 eV and ΔH=0.168 eV, respectively. The insulating behavior is consistent with the previous experiment reports and the theoretical calculation, which is possibly attributed to the suppression of orbital degree of freedom, resulting from the elongation of CrO6 octahedron and the narrow band width induced by the two-dimensional crystal structure.