Studies of the effect of internal and hydrostatic pressure on the structure and transport properties of La2/3Ca1/3MnO3 thin films

Lanthanum manganites belong to the perovskite type Mott insulators. They sh ow a doping dependent drastic modification of conductivity including a meta l-insulator transition associated with ferromagnetic ordering. We investiga ted La2/3Ca1/3MnO3 thin films, a member of this class of material showing a colossal magnetoresistance. Application of internal and external pressure can be used to modify the electronic and magnetic properties of this materi al. It has been shown that, in La2/3Ca1/3MnO3, as the band width for the it inerant e, electrons broadens, it causes an enhancement of the ferromagneti c coupling and consequently an increase of the metal-insulator transition t emperature T-MI, which is close to the ferromagnetic transition temperature T-MI. Thin films were deposited on SrTiO3 (STO) single crystals using the pulsed laser deposition technique. In this study we prepared films with dif ferent T-MI by choosing an appropriate depositing temperature, annealing co ndition and thickness range. We studied the effect of hydrostatic pressures on the in-situ annealed films in order to investigate the effect of extern al pressure on T-MI and resistivity as a function of annealing. Due to latt ice mismatch between film and substrate we introduced controllable biaxial strain. The increase of lattice parameters and T-MI shows the relaxation pr ocess by varying the film thickness and by annealing thin layers. Our resul ts are a contribution to the clarification of the interplay between the mic roscopic structure of Mn-O-Mn units with the macroscopic transport properti es. (C) 2001 Elsevier Science B.V. All rights reserved.