Anomalous strain relief and physical properties of La_0.5Ca_0.5MnO₃ films

La_0.5Ca_0.5MnO₃ films were grown using pulsed laser deposition. Several factors, such as variation of substrates, interface effects, and annealing effects, influencing the properties of the grown films were investigated. As-grown films on LaAlO₃ substrates showed anomalous strain relief; they had strained and partly relaxed layers, both of which had tetragonal structures. On SrTiO₃ substrates, only coherently strained layers were observed. Such a difference of growth behaviors cannot be explained solely in terms of lattice mismatch since only partly relaxed layers appeared on LaAlOs substrates with strained SrTiO₃ interlayers. Annealing treatments relieved the strains in the films, and relaxed layers were obtained after annealing. The transport and the magnetic properties of the annealed films were quite different from those of the as-grown films.