Influence of strain relaxation on magnetotransport properties of epitaxialLa0.7Ca0.3MnO3 films

Abstract

In this paper, we study the effect of strain relaxation on the magnetotransport properties ofLa0.7Ca0.3MnO3 (LCMO) epitaxial films (200 nm thick), which were deposited by pulsed laser depositiontechnique under identical conditions. All the films are epitaxial and have a cubic unit cell. Theamount of strain relaxation has been varied by taking three different single crystal substrates ofSrTiO3,LaAlO3 and MgO. It has been found that for thicker films the strain becomes relaxed and producesa variable amount of disorder depending on the strength of strain relaxation. The magnitude oflattice relaxation has been found to be 0.384%, 3.057% and 6.411% for film deposited onSrTiO3,LaAlO3 and MgO respectively.The films on LaAlO3 and SrTiO3 showhigher TIM (insulator–metal transition temperature) of∼243 and 217 K respectivelyas compared to TIM of ∼191 K for the film on MgO. Similarly the Curie temperatureTC of the filmson SrTiO3 andLaAlO3 is sharper and hasvalues of ∼245 and 220 Krespectively, whereas the TC of the film on MgO is ∼186 K. A higher degree of relaxation creates more defects and hence theTIM (TC) of the film on MgO is significantly lower than those ofSrTiO3 and LaAlO3. We have adopted a different approach to correlate the effect of strain relaxation on themagnetotransport properties of LCMO films by evaluating the resistivity variation throughMott’s variable range hopping (VRH) model. The variable presence of disorder in thesethick films due to lattice relaxation, which have been analysed through Mott’s VRH model,provides strong additional evidence that the strength of lattice relaxation producesdisorder dominantly by an increase in density of defects such as stacking faultsand dislocations, which affect the magnetotransport properties of thick epitaxialLa0.7Ca0.3MnO3 films.