Strain-enhanced phase separation affecting electro- and magnetotransport in La0.67Ca0.33MnO3 films
Journal article, 2004
Biaxial strain during nucleation influences phase separation into ferromagnetic (metallic) and nonferromagnetic (insulating) regions and that, in turn, markedly affects the electric transport of a manganite film. A 40-nm-thick La0.67Ca0.33MnO3 film, coherently constrained by a (001)LaAlO3 substrate, possesses a noticeably contracted unit cell volume (Veff[approximate]56.70 Å3) as compared with that of a stoichiometric bulk sample. It corresponds to a higher relative concentration (45%) of tetravalent manganese ions in the manganite layer than that in the target (33%). The resistivity rho(T) curve of the strained film peaks twice in the range 4.2300 K. The charge transport of strained La0.67Ca0.33MnO3 films is non-ohmic at T<130 K. A magnetic field H linearizes the currentvoltage characteristic, but its impact on rho(T) and IV decreases at low temperature. The unusual features in the electro- and magnetotransport properties of thin La0.67Ca0.33MnO3/(001)LaAlO3 films are ascribed to a strain-enhanced phase separation, which is also responsible for the large magnetoresistance (up to 90%) at 5 T within a broad temperature range. Thicker films experience a relaxation, a smaller resistivity, and less non-linear properties.