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Information × Registration Number 0203U006409, 0100U002127 , R & D reports Title Investigations of magnetic and transport properties of perovskite-like oxides with the colossal magnetoresistance and development of the functional elements on their basis popup.stage_title Head Prokhorov Valeriy Georgiyovich, Registration Date 08-05-2003 Organization Institute for metal physics NAS Ukkraine popup.description2 The complex investigations of the magnetic and transport properties of the films for following compositions: Pr_0.65Ca_0.35MnO_3; La_1-xSr_xCoO_3 (0.15 < x < 0.5); La_1-xCa_xMnO_3-d (0.1 < x < 0.3; 0 < d < 0.2) and La_0.8Sr_0.2MnO_3, prepared by method of pulse laser deposition and magnetron sputtering, were carried out in this work. The charge- and magnetic-ordering effect controlled by the lattice strain, owing to the epitaxial growth on the two types of substrates (SrTiO_3 and YSZ), was observed in the Pr_0.65Ca_0.35MnO_3 films. The energy gap between charge-ordered and charge-disordered states was obtained experimentally for this compound. It was shown, that the long-time ageing (one year) of the La_0.5Sr_0.5CoO_3-d film leads to depletion of the oxygen up to d = 0.8. The accumulation of the oxygen vacancies provides not only the charge-redistribution between cobalt ions with different valency, but forms the topological disordering in conducting channel of Co-O-Co chains, as well. The observedgrowth in a resistance with decreasing temperature in La_0.5Sr_0.5CoO_2.92 with oxygen deficiency is governed by the weak localization of carriers owing to the introduced disordering in the oxygen ions distribution, and is not connected with the thermal activated or the hopping conductivity. Analysis of the magnetization curves displays that the aged La_0.5Sr_0.5CoO_2.92 film undergoes the additional magnetic transition at T = 50 K, which is accompanied by a small increase in magnetic moment. The large difference between FC and ZFC magnetization curves M(T) testifies to the considerable inhomogeneity in distribution of the magnetic moments in films (0.35 < x < 0.5) and confirms the existence of the FM ordered regions divided by the matrix of the disordered spins ( spin-cluster state). It was observed, that as-deposited La_0.8Ca_0.2MnO_3-d thin films become unstable to the phase transition during long-time ageing in area. Two crystalline phases with different oxygen concentration, cubic La_0.8Ca_0.2MnO_2.92 and rhombohedral La_0.8Ca_0.2MnO_2.84, form in the film, that is confirmed by magnetic and transport measurements. Accumulation of the non-uniform distributed lattice strains can be stimulate not only charge-phase separation, but lead to the change of crystal lattice. Magnetic and transport properties of La_0.8Sr_0.2MnO_3 films deposited onto LaAlO_3 (001) substrate and La_0.8Ca_0.2MnO_3 layer have been investigated in the wide temperature range. It was shown, that the electron and magnetic transitions of the La_0.8Sr_0.2MnO_3 film, deposited onto La_0.8Ca_0.2MnO_3 layer, turn out to be at higher temperature than that grown on LaAlO_3 substrate. Increasing in the magneto-resistance and the ferromagnetic ordering in two-layer sample are explained by the relaxation of the lattice strain. It is confirmed the truth of the Millis model for the description of the ferromagnetic properties of CMR films. The appearance of the charge-ordered state in the thin La_0.7Ca_0.3MnO_2.9 films is connected with the change inthe crystal symmetry and the decreasing of the unit cell volume that appears owing to the epitaxial growth rather than with the oxygen deficiency as it was suggested early. The observed enhancement in the temperature of magnetic ordering in the film with the artificial compression of crystal lattice opens up wide possibilities for the controlling of spin states in these compounds. The magnetic and the transport properties of the nano-crystalline twinned La_0.65Ca_0.35MnO_3 films have been investigated in the temperature range of 77 - 300 K. It was observed that the increase in transport current leads to the formation of COI state in the temperature range below the MI transition. Observed correlation between the formation and the growth of FM and COI phases is explained by the non-uniform distribution of the transport current between metal-like and insulating domains, which is accompanied by the metal-insulator transition. Thermal cycling of the film leads to the formation of the non-equilibrium state in the ensemble of COI domains and to appearance of giant oscillations in the resistance, up to 100%. It was suggested that the main reason for this effect is the martensate nature of the charge-ordered transition. Product Description popup.authors popup.nrat_date 2020-04-02 Close