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Magnetic structure of a CaMnO2.75 crystal with ordered oxygen vacancies
Authors:S F Dubinin  N N Loshkareva  S G Teploukhov  A V Korolev  É A Neĭfel’d  V E Arkhipov  V D Parkhomenko  Yu P Sukhorukov  A M Balbashov
Institution:(1) Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S. Kovalevskoĭ 18, Yekaterinburg, 620041, Russia;(2) Energy Research Institute, Russian Academy of Sciences, ul. Vavilova 44/2, Moscow, 117935, Russia
Abstract:The magnetic state of a CaMnO3 ? δ crystal with ordered oxygen vacancies (for δ = 0.25, when the numbers of Mn4+ and Mn3+ ions in the manganite are equal to each other) is studied using neutron diffraction. Magnetic scattering in the CaMnO2.75 crystal in the ground state is determined by the wave vector (1/2, 1/2, 1/2)2π/a c (G-type antiferromagnetic order). In the crystal, long-range magnetic order disappears at the temperature T N = 116 K, whereas short-range magnetic order is retained up to 240 K. It is shown that the instability of the G-type structure in the temperature range 60 K < T < T N is associated, in many respects, with the formation of the C′ antiferromagnetic phase in the bulk of the crystal. The structure of the C′ antiferromagnetic phase involves chains with Mn3+-Mn4+ ferromagnetic interaction. A comparison of the results of the neutron diffraction investigations with the experimental data on the magnetic characteristics and electrical resistivity demonstrates that the specific features revealed in the spin system of the CaMnO2.75 crystal are governed directly by the competition of the Mn3+-Mn4+ ferromagnetic double exchange with the antiferromagnetic superexchange between manganese ions.
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