Magnetic origin and oxydation states of cations in the TC∼440 K ferrimagnet Sr 2Cu(Re 0.69Ca 0.31)O 6

Abstract

We have studied crystal structure, ionic-model energy calculation, and electron energy-loss spectroscopy (EELS) for a new magnetic ordered-perovskite Sr 2Cu(Re 0.69Ca 0.31)O 6 in order to determine oxidation states of the Re and Cu ions. All of the experimental results of the bond-valence sum, the static energies, and the energy-loss near-edge structure (ELNES) in EEL spectra consistently indicated that the Re 7+, Cu 2+ and Cu 3+ valence states are realized in the compound. This is evident that the Cu spins are responsible for the magnetism in the phase. By considering the Cu 3d and O 2p orbital shapes, we concluded that the unusually high Curie temperature, T C∼440 K, originates in ferrimagnetism with strongly coupled Cu spins in a three dimensional (3-D) network of the Cu 2+–O–Cu 3+–O–Cu 2+ bond in structure.