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

Abstract Magnetocaloric studies reported here on a 7.6 nm thin film of La 0 . 7 Sr 0 . 3 MnO 3 grown on SrTiO 3 substrate show that the film is magnetically inhomogeneous since the - ∆ S M (magnetic entropy change) vs. temperature data has two broad peaks, one centered near T ∼ 220 K and the other centered near T ∼ 270 K. Combining these results with magnetic studies show that T B ∼ 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 TC ∼290 K. Detailed analysis of - ∆ S M (T, H) vs. T data is used to determine the volume fraction of the superparamagnetic (SPM) to ferromagnetic (FM) phases to be ∼ 17% 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 - ∆ 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.