Strain-Induced Spin States in Atomically Ordered Cobaltites

Abstract

Epitaxial strain imposed in complex oxide thin films by heteroepitaxy is recognized as a powerful tool for identifying new properties and exploring the vast potential of materials performance. A particular example is LaCoO(3), a zero spin, nonmagnetic material in the bulk, whose strong ferromagnetism in a thin film remains enigmatic despite a decade of intense research. Here, we use scanning transmission electron microscopy complemented by X-ray and optical spectroscopy to study LaCoO(3) epitaxial thin films under different strain states. We observed an unconventional strain relaxation behavior resulting in stripe-like, lattice modulated patterns, which did not involve uncontrolled misfit dislocations or other defects. The modulation entails the formation of ferromagnetically ordered sheets comprising intermediate or high spin Co(3+), thus offering an unambiguous description for the exotic magnetism found in epitaxially strained LaCoO(3) films. This observation provides a novel route to tailoring the electronic and magnetic properties of functional oxide heterostructures.

Role of entropy and structural parameters in the spin-state transition of LaCoO3

“…Interest in this compound has also been enhanced in light of recent discoveries of ferromagnetism induced by Sr (hole) doping [26][27][28][29] , and by experiments reporting strain induced magnetism in epitaxially grown thin films. [30][31][32][33][34][35][36] Additionally, there have been reports of the emergence of a striped phase in thin films (with alternating LS and HS/IS regions) 37 , as well as the presence of low temperature ferromagnetism in experiments performed on LaCoO 3 nanoparticles 38 . Furthermore, there have also been experiments conducted on single crystals of LaCoO 3 in the presence of a strong magnetic field [39][40][41][42] which have reported the presence of multiple metamagnetic transitions, which have been attempted to be explained by spin-state superlattices as well as excitonic condensation.…”

Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films

“…[15][16][17][18][19] Recent computational studies have investigated the effects of epitaxial strain on oxygen vacancies in conventional perovskites. While they predict that the activation energies of these vacancies can be tuned by tenths of an eV under modest strains of a few 3 percent, the initial energies of >2 eV render these changes relatively insignificant at reduced temperatures.…”

Strain tuning of electronic structure inBi4Ti3O12−LaCoOChoi1, Lee2 2015Phys. Rev. BSelf Cite18120View full textAdd to dashboardCite

“…As epitaxial strain is an efficient tuning parameter for various physical properties of TMOs [22][23][24], we were able to observe detailed crystal and electronic structure evolution with Co incorporation into BiT depending on the strain state. In particular, we observed a systematic change in the lattice parameters and a subsequent decrease in the optical transition energy between the electronic states with Co incorporation.…”