An investigation on strain and magnetic properties of perovskite manganite superlattice films

The mixed-valence perovskite manganites attracted much attention because of their interesting electro-magnetic properties, and strain modulation on magnetic properties of perovskite manganites is worth exploring. In this paper, [La0.8Ca0.2MnO3/La0.5Ca0.5MnO3](20) superlattice films with different La0.8Ca0.2MnO3 layer thicknesses are prepared by pulsed laser deposition (PLD). The crystal structures (lattice constants) of samples are measured by X-ray diffraction (XRD). The strain of the films is determined according to their crystal structures. The magnetic hysteresis loops (M-H loops) and magnetization versus temperature (M-T) curves of these superlattice films are measured by the physical property measurement system (PPMS). From the M-H loops, the coercive field (H-C) of the samples can be measured. From the M-T curves, the Curie temperature (T-C) of the samples can be obtained. All samples show a ferromagnetic to paramagnetic transition at T-C, and the [La0.8Ca0.2MnO3/La0.5Ca0.5MnO3](20) sample with the La0.8Ca0.2MnO3 layer thicknesses of 72 angstrom has an antiferromagnetic Neel transition at T-N. According to the strain state and magnetic phases, the magnetic properties are comprehensively analyzed. It is found that with the increase of ferromagnetic La0.8Ca0.2MnO3 layer thickness, the ferromagnetic phase is increased, and the double exchange effect can also be enhanced, resulting in the increase of T-C. When the thickness of La0.8Ca0.2MnO3 reaches 96 angstrom, the uneven strain distribution in the superlattice can induce the reduction of ferromagnetic phase compared with antiferromagnetic phase (even antiferromagnetic phase starts to appear), and the double exchange effect can be weakened, and finally leading to the decrease of T-C. In addition, with increasing the La0.8Ca0.2MnO3 layer thickness, H-C gradually decreases. The change of H-C is related to strain states and magnetic phase interactions in the samples. The analysis of the strain and magnetism can contribute to the understanding of perovskite manganite superlattice films.