Ferromagnetic order in epitaxially strainedLaCoO3thin films

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

“…In our previous work, using local spin density approximation combined with the Hubbard U correction (LSDA+U), we have shown that a ferromagnetic state based on a homogenous intermediate spin (IS) state (S=1) can be stabilized above 3.8% tensile strain [10]. The ferromagnetic IS state is, however, inconsistent with two experimentally determined properties of strained LCO: the IS state is half-metallic while experiment shows that strained LCO is insulating [7], and a rather high critical strain of 3.8% is required, which is somewhat higher than that in experiment (~2%) [5][6][7][8][9][10]. Most recently, using a LDA+U approach, Hsu et al have shown that a HS/LS mixed state has a lower energy than that of the IS state in tensile-strained LCO on STO [28].…”

“…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].…”

“…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]. Since the first demonstration by Fuchs et al using films grown by pulsed laser deposition (PLD) [5] and by our group using molecular beam epitaxy (MBE) [10], several intriguing properties of strained LCO have been found experimentally. In addition to transport measurements showing insulating behavior for tensile-strained FM LCO [7], Fuchs and co-workers have also shown that both the population of higher spin states and the magnetization in LCO increase as tensile strain increases [6].…”

Lattice mismatch accommodation via oxygen vacancy ordering in epitaxial La0.5Sr0.5CoO3-δ thin films

“…LaCoO 3 provides a good example as it adopts a low-spin "non-magnetic" ground state in bulk, but exhibits strain-stabilized ferromagnetism in films. [1][2][3] In the doped case, e.g., in bulk La 1-x Sr x CoO 3-δ (LSCO), substitution of Sr 2+ for La 3+ changes the Co valence, inducing metallic ferromagnetism, 4 but also O vacancies. Without the use of high pressures, these vacancies form in high concentrations for x > 0.5-0.6, 5 eventually forming ordered superstructures, as exemplified by Brownmillerite SrCoO 2.5 (SCO).…”

“…For STO(001)/LSCO and LAO(001)/LSCO, the (013) reflection was chosen. For STO(110)/LSCO, the fourfold in-plane symmetry is broken, and we chose the (310) and (222) reflections to probe two orthogonal high symmetry in-plane directions ( [1][2][3][4][5][6][7][8][9][10] and [001]). In all cases, white crosses mark the positions of the fully strained (pseudomorphic) and fully relaxed (bulk) LSCO reflections.…”