Publication: Spin and orbital Ti magnetism at LaMnO3/SrTiO3 interfaces
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2010-09
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In systems with strong electron-lattice coupling, such as manganites, orbital degeneracy is lifted, causing a null expectation value of the orbital magnetic moment. Magnetic structure is thus determined by spin–spin superexchange. In titanates, however, with much smaller Jahn–Teller distortions, orbital degeneracy might allow non-zero values of the orbital magnetic moment, and novel forms of ferromagnetic superexchange interaction unique to t_2g electron systems have been theoretically predicted, although their experimental observation has remained elusive. In this paper, we report a new kind of Ti^3+ ferromagnetism at LaMnO_3/SrTiO_3 epitaxial interfaces. It results from charge transfer to the empty conduction band of the titanate and has spin and orbital contributions evidencing the role of orbital degeneracy. The possibility of tuning magnetic alignment (ferromagnetic or antiferromagnetic) of Ti and Mn moments by structural parameters is demonstrated. This result will provide important clues for understanding the effects of orbital degeneracy in superexchange coupling.
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© 2010 Macmillan Publishers Limited.
We thank Andrew Millis and Giniyat Khaliullin for stimulating discussions. J.G.-B. thanks the Spanish Ministry of Science and Innovation (MICINN) for financial support through the Specialization in International Organizations fellowship. This work was supported by Spanish MICINN Grant MAT 2008 06517, Consolider Ingenio CSD2009-00013 (IMAGINE), CAM S2009-MAT 1756 (PHAMA). Work at ORNL was supported by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Some XMCD experiments were conducted with the approval of JASRI (proposal no. 2007B1516) and supported by UK EPSRC Grants EP/F062729 and EP/G056463/1.
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