Geometric influence on the Net Magnetic Moment in LaCoO₃ thin films

The different magnetic behaviors of LaCoO₃ films grown on LaAlO₃ and SrTiO₃ are related to the Co-O-Co bond angles and the constraints imposed on the Co-O bond lengths by the substrate geometries. Long-range magnetic order occurs in the films grown on SrTiO₃ below T = 90 K because the Co-O-Co bond angle exceeds the critical value of 163° due to the biaxial tensile strain imposed by the substrate. A LaAlO₃ substrate, on the other hand, prevents magnetic-long-range order at low temperatures. Here, we will present a common basis for these strikingly different magnetic behaviors under different strain conditions using x-ray diffraction and magnetization measurements on PLD grown LaCoO₃ thin films. The fundamental antiferromagnetic interaction in the films was characterized using Curie’s law above the critical temperature, and the ensuing ferromagnetic moment was analyzed in view of the strain induced by the substrate, and the results were correlated with the purported Co-O-Co bond angle determined from x-ray diffraction.