Size effect of substitutional alkaline-earth elements on the electrical and structural properties of LaMnO₃ films

Tolerance factor controlled Mn-based colossal magnetoresistance (CMR) thin films (La_0.7Ca_0.3MnO₃, La_0.7Sr _0.3MnO₃, La_0.7Sr_0.11Ba _0.19MnO₃, and La_0.7Ba_0.3MnO ₃) which have the same content of divalent cation and Mn ³⁺/Mn⁴⁺ ratio were deposited on amorphous SiO ₂/Si substrate by rf magnetron sputtering at 350°C substrate temperature. Post annealing treatment for 1 h at 600°C was also carried out to investigate the effects of internal strain and chemical bonding nature from different divalent ions on the electrical properties of the films by maintaining a similar crystalline state. The films crystallized with pseudo cubic structure in spite of different tolerance factors. The sheet resistance of films changed according to crystallization and Mn-O bonding character. Mn L-edge X-ray absorption spectra revealed that Mn³⁺/Mn⁴⁺ ratio did not change in all the films and Mn 2p core level X-ray photoelectron spectra showed that Mn-O bonding property changed to more covalence as increasing tolerance factor by substitution with larger size divalent cation. O K-edge X-ray absorption spectra observed t_2g and e_g electron states and low resistivity after post anneal could be explained by the promotion of electrons to low binding energy state. Temperature coefficient of resistance (TCR) values were about -2.24 ∼ -2.57 %/K of as deposited CMR films and these values were reasonable for uncooled microbolometer applications.