Spin and orbital Ti magnetism at LaMnO3/SrTiO3 interfaces

Abstract

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.

Tuning the Two-Dimensional Electron Liquid at Oxide Interfaces by Buffer-Layer-Engineered Redox Reactions

“…Here we identify both octahedrally Oh and tetrahedrally Td coordinated Mn 2+ , along with a dip in the oxygen concentration [supporting information], suggesting the formation of the oxygen deficient brownmillerite structure in a thin layer at the interface. Such a structural transformation has been observed before for LAO and STO film growth on LSMO buffer layers 34 It has been previously revealed that when the LSMO is strongly strained on STO (such as at t≤ 6uc), orbital reconstructions result in a situation that the Mn eg levels become comparable to or even higher than the Ti t2g electron level 36 , in this case, charge transfer could occur from Mn 2+ to STO (as indicated by the arrow in the upper schematic of Fig. 3(c)).…”

“…Below 4 uc, the polar potential of the LSMO is below the threshold for electronic reconstruction, and the conduction in STO remains dominated by the redox reaction. Above 6 uc, besides lattice distortions 36 Fig.2 …”

Cationic-vacancy-induced room-temperature ferromagnetism in transparent, conducting anatase Ti 1− x Ta x O 2 ( x ∼0.05) thin films

“…By the same analogy, when we compare the pure TiO 2 with Ti 1−x Ta x O 2 (x ∼ 0.05) films grown at 750 • C (figure 9b), the t 2g peak of the latter decreases in height with respect to the former, which (together with the support of XPS data) suggests no or very reduced V Ti . In retrospect, it is important to note that the SXMCD signal in the present case is different from the one observed in LaMnO 3 /SrTiO 3 , which originates from the Ti 3+ states present at its interface, as recently reported by Garcia-Barriocanal et al [41]. This also suggests that the strong SXMCD signal in Ti 1−x Ta x O 2 (x ∼ 0.05) films grown at 600 • C does not arise from the Ti 3+ defect and is most likely from the V Ti .…”

Reversible electric-field control of magnetization at oxide interfaces

“…The phenomenon was first reported in cuprate YBa 2 Cu 3 O 7 (YBCO)/manganite La 0.7 Ca 0.3 MnO 3 (LCMO) interfaces where charge transfer and orbital reconstruction induce a net magnetic moment in the Cu sublattice, with antiferromagnetic coupling between Mn and Cu 15,16 . The effect was also observed at PrBa 2 Cu 3 O 7 (PBCO)/LCMO interfaces 17 , and also at other interfaces between magnetic and non-magnetic oxides [18][19][20] , suggesting the generality of the phenomenon.…”