Influence of strain relaxation on magnetotransport properties of epitaxial La0.7Ca0.3MnO3 films

摘要

In this paper, we study the effect of strain relaxation on the magnetotransport properties of La0.7Ca0.3MnO3 (LCMO) epitaxial films (200 nm thick), which were deposited by pulsed laser deposition technique under identical conditions. All the films are epitaxial and have a cubic unit cell. The amount of strain relaxation has been varied by taking three different single crystal substrates of SrTiO3, LaAlO3 and MgO. It has been found that for thicker films the strain becomes relaxed and produces a variable amount of disorder depending on the strength of strain relaxation. The magnitude of lattice relaxation has been found to be 0.384%, 3.057% and 6.411% for film deposited on SrTiO3, LaAlO3 and MgO respectively. The films on LaAlO3 and SrTiO3 show higher T-IM (insulator-metal transition temperature) of similar to 243 and 217 K respectively as compared to TIM of similar to 191 K for the film on MgO. Similarly the Curie temperature T-C of the films on SrTiO3 and LaAlO3 is sharper and has values of similar to 245 and 220 K respectively, whereas the TC of the film on MgO is similar to 186 K. A higher degree of relaxation creates more defects and hence the TIM ( TC) of the film on MgO is significantly lower than those of SrTiO3 and LaAlO3. We have adopted a different approach to correlate the effect of strain relaxation on the magnetotransport properties of LCMO films by evaluating the resistivity variation through Mott's variable range hopping (VRH) model. The variable presence of disorder in these thick films due to lattice relaxation, which have been analysed through Mott's VRH model, provides strong additional evidence that the strength of lattice relaxation produces disorder dominantly by an increase in density of defects such as stacking faults and dislocations, which affect the magnetotransport properties of thick epitaxial La0.7Ca0.3MnO3 films.