Magnetic and electronic properties of the ferroelectric-photovoltaic ordered double perovskite CaMnTi₂O₆ investigated by x-ray absorption spectroscopies

Abstract

The ferroelectric and magnetic phases of the double perovskite CaMnTi₂O₆ with A-site order have been investigated by soft x-ray absorption and magnetic circular dichroism. All spectra point to a very ionic state of divalent Mn and tetravalent Ti atoms. The effects of the crystal field produced by O ligands around tetravalent titanium and the dissimilar Mn1 and Mn2 sites were investigated. Both the so-called square-planar and the octahedrally coordinated Mn sites spectroscopically contribute in a rather similar way, with little influence by the oxygen environment. Multiplet calculations suggest a small O2p-Ti3d charge-transfer component in the FE phase. Magnetic symmetry calculations were performed to determine probable configurations of Mn spins compatible with the acentric P4₂mc structure and, in combination with the computational magnetic results in Inorg. Chem. 56, 11854 (2017), we have identified the P4₂′m′c as the most likely magnetic space group keeping invariant the unit cell below TN. This symmetry forces the sign of the magnetic coupling along the Mn columns parallel to c to reverse with respect to the coupling between neighboring columns. Below TN, the dichroic magnetization loops at the MnL₃ edge confirm the absence of spontaneous ferromagnetism, although a very small field-induced spin polarization was detected in the sample.