Observation of the strain-driven charge-ordered state in La0.7Ca0.3MnO3-d thin film with oxygen deficiency

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Анотація

The magnetic and transport properties of La_0.7Ca_0.3MnO_3-d films with an oxygen deficiency (d≃ 0.1) and a La_0.9Ca_0.1MnO₃ film with the stoichiometric oxygen content are investigated in a wide temperature range. It is shown that the charge-ordered insulating (COI) state is observed for a La_0.7Ca_0.3MnO_2.9 film with thickness d ≤ 30 nm, which manifests mainly a cubic crystal structure with an anomalously small lattice parameter for this composition. An increase in the film thickness (d ≃ 60 nm) leads to a structural transition from the lattice-strained cubic to the relaxed rhombohedral phase, is accompanied by a shift of the Curie point (T_C) to lower temperature and a frustration of the COI state. The magnetic and transport properties of the La_0.7Ca_0.3MnO_2.9 film with d ≃ 60 nm are similar to those exhibited by the optimally oxygen-doped La_0.9Ca_0.1MnO₃ film. It is concluded that the formation of the COI state in the La_0.7Ca_0.3MnO_3-d compound is governed by a compression of the crystal lattice rather than accumulation of oxygen vacancies, the low doping of the substituted divalent ions, or electronic phase separation.