Magnetic ground state and the spin-state transitions in YBaCo2O5.5 |
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Authors: | D. P. Kozlenko Z. Jirák N. O. Golosova B. N. Savenko |
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Affiliation: | (1) Frank Laboratory of Neutron Physics, JINR, 141980 Dubna Moscow Reg., Russia;(2) Institute of Physics, Cukrovarnická 10, 162 53 Prague 6, Czech Republic |
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Abstract: | The crystal and magnetic structure of the perovskite-like, oxygen deficient cobalt oxide YBaCo2O5.5 has been studied by means of neutron and X-ray diffraction in the 10–300 K temperature range. The magnetic ground state is characterized by a coexistence of two distinct antiferromagnetic phases. In the first one, the ionic moments of high-spin Co3+ ions in the pyramidal sites are ordered in a spiral arrangement, while octahedral sites are non-magnetic due to presence of low-spin Co3+ ions. The arrangement in the second phase is collinear of the G-type, with non-zero moments both in pyramidal (high-spin Co3+ ions) and octahedral sites (presumably a mixture of the low- and high-spin states). With increasing temperature, at 260–300 K, the system develops a gradual structural transformation, which is associated with appearance of spontaneous magnetic moment. This process is related to a thermally induced reversion of low- and high-spin states at the octahedral sites to the intermediate-spin Co3+ states, resulting in an insulator-metal transition at TC ≈ TIM ≈ 295 K. |
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Keywords: | KeywordHeading" >PACS 75.25.+z Spin arrangements in magnetically ordered materials 61.05.fm Neutron diffraction |
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