Strain Dependence of Magnetic and Transport Properties in Half-Doped La0.5Ca0.5MnO3 Films

Tensile strain effects on the magnetic and electrical properties of La_0.5Ca_0.5MnO₃ (LCMO₅) films deposited on SrTiO₃ (001) substrates are investigated with varying the thickness of LCMO₅ from 16.5 to 62.2 nm. A microstructure analysis indicates that the film remains tensile-strain state with its thickness thinner than 50 nm. Magnetic measurements show that the ferromagnetic (FM) transition temperature (T_C) of the films increases from 250 to 265 K with the film evolving from tensile to relaxed state. Meanwhile, the saturation magnetization at 5 K increases from 21.88 to 43.88 emu/cm³. It is interesting to find that colossal magnetoresistance is drastically enhanced from 18% to 740% with increasing the film thickness from 22.2 to 62.2 nm, which is attributed to the relaxation of tensile strain in association with an enhancement of FM interaction within an antiferromagnetic matrix.