期刊
PHYSICAL REVIEW LETTERS
卷 105, 期 20, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.105.207201
关键词
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资金
- NRF-CRP [NRF-G-CRP 2007-05, NRF2008NRF-CRP002-024]
- NUS YIA
- NUS Cross Faculty
- FRC
- DOE [DE-AC02-98CH10886]
- CMSN and NNSFC [10774091]
- NUS [C-380-003-003-001, A*STAR/MOE RP 3979908M, A*STAR 12 105 0038]
We report direct evidence of room-temperature ferromagnetic ordering in O-deficient ZnO:Cu films by using soft x-ray magnetic circular dichroism and x-ray absorption. Our measurements have revealed unambiguously two distinct features of Cu atoms associated with (i) magnetically ordered Cu ions present only in the oxygen-deficient samples and (ii) magnetically disordered regular Cu2+ ions present in all the samples. We find that a sufficient amount of both oxygen vacancies (V-O) and Cu impurities is essential to the observed ferromagnetism, and a non-negligible portion of Cu impurities is uninvolved in the magnetic order. Based on first-principles calculations, we propose a microscopic indirect double-exchange model, in which alignments of localized large moments of Cu in the vicinity of the VO are mediated by the large-sized vacancy orbitals.
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