Magnetocaloric investigations show magnetic inhomogeneity in a 7.6 nm thin film of La0.7Sr0.3MnO3/SrTiO3

Magnetocaloric studies reported here on a 7.6 nm thin film of La0.7Sr0.3MnO3 grown on SrTiO3 substrate show that the film is magnetically inhomogeneous since the -Delta S-M (magnetic entropy change) vs. temperature data has two broad peaks, one centered near T similar to 220 K and the other centered near T similar to 270 K. Combining these results with magnetic studies show that T-B similar to 220 K represents the blocking temperature of spin clusters present in the surface layer whereas the rest of the film has ferromagnetic to paramagnetic transition at the Curie temperature T-C similar to 290 K. Detailed analysis of -Delta S-M (T, H) vs. T data is used to determine the volume fraction of the superparamagnetic (SPM) to ferromagnetic (FM) phases to be similar to 17% to similar to 83% at 4 kOe. The dependence of the RCP (relative cooling power) and the volume fraction of SPM and FM phases on the applied magnetic field up to H = 4 kOe is evaluated by fitting the -Delta S-M vs. T data to two Gaussian functions. This analysis shows that the RCP and the volume fraction of the FM (SPM) phase increases (decreases) with an increase in H. (C) 2020 Elsevier B.V. All rights reserved.