TRANSPORT ANISOTROPY IN PLD-MADE La_(0.75)Sr_(0.25)MnO3 FILMS

摘要

A sequence of epitaxial La_(0.75)Sr_(0.25)MnO3 (LSMO) films with thickness ranging from 2400 to 50 A have been prepared by pulsed laser deposition onto (110) SrTiO3 (STO) substrates. Com-pared with our previous results on LSMO/STO(100) films, films on STO(110) substrates exhibit strong anisotropy of electrical resistivity rho. rho measured in [110] direction is comparable with the resistivity of LSMO/STO(100) films while rho in [001] direction is 25 times higher than in STO(100) case. The maximum value of anisotropy parameter rho_([001]) / rho_([110]) = 25 is reached for thick films at the low temperature of 90 K. Distinct crossover from 3D to 2D case has been ob-served. For thick films anisotropy monotonously decreases with the temperature increase. Films thinner than 200 A exhibit a maximum of anisotropy parameter, which shifts to lower tempera-tures with the thickness decrease. The maximum temperature coefficient of resistivity (TCR) was found to be around 2% if measured along [001] direction and about 50 % higher in [110] in-plane direction. We explain the observed effects in terms of the crystalline properties of fabri-cated films.