Local atomic and electronic structures of epitaxial strained LaCoO3thin films

The effects of Co3O4on the structure and unusual magnetism of LaCoO3

“…Fuchs et al found that highly stressed LCO films exhibited a decreasing ferromagnetic order to depths of 100 nm when deposited on (LaAlO 3 ) 0.3 (SrAl 0.5 Ta 0.5 O 3 ) 0.7 (LSAT) substrates. [40] Other experiments indicate ferromagnetism persisting for 20 to 30 nm into LCO [18,20], while experiments on nanoparticle LCO suggest it is in the range of 20 -100 nm. [43,44] Based on these studies, we roughly estimate that ferromagnetism penetrates our particles to a depth of 20 to 100 nm.…”

“…Sterbinsky et al reported that a 20 nm film of LCO deposited on a SrTiO 3 (STO) substrate had a significantly elongated in-plane Co-O bond length and a shortened out-of-plane bond length compared to the bulk value. [18] They estimated Co-O-Co angles of 168 • and 159 • for the in-and out-of-plane bond lengths, respectively. Another thin film study by Fuchs et al connected structural distortions to the presence of ferromagnetic order, estimating that the Co-O-Co angle above which there can be ferromagnetism is approximately 160 • .…”

“…Thin film studies [16,18,40] have suggested that LCO thin films grown on certain substrates exhibit ferromagnetic long-range order, in particular when the substrate induces tensile stress at the interface with LCO. Sterbinsky et al reported that a 20 nm film of LCO deposited on a SrTiO 3 (STO) substrate had a significantly elongated in-plane Co-O bond length and a shortened out-of-plane bond length compared to the bulk value.…”

“…A previous study suggested that ferromagnetic effects are induced by strain from Co-impurities in bulk powders of LCO [17] and that the Co-O-Co bond angle, γ, is a structural indicator of the strength of ferromagnetic ordering. Other groups, however, have singled out changes in the Co-O bond length [14,18], the amount of rhombohedral distortion [13], or the unit cell volume [19] as direct mechanisms for ferromagnetic ordering.…”

Strain-driven spin-state transition and superexchange interaction in LaCoO3:Abinitiostudy

“…Furthermore, strain engineering in these oxide heterostructures opens up routes for creating novel electronic phases [2][3][4]. An exciting example is the recent demonstration of biaxial tensile strain stabilizing an insulating ferromagnetic (FM) ground state in LaCoO 3 (LCO) [5][6][7][8][9][10][11][12][13][14]. Though LCO is a classic example of a correlated 3d transition metal perovskite oxide [15,16], FM correlation has never been observed for the bulk ground state where the Co 3+ ions exist in the so-called low spin (LS) state (total spin per Co S=0) [15].…”