Insights into the magnetic dead layer in La0.7Sr0.3MnO3 thin films from temperature, magnetic field and thickness dependence of their magnetization

Experimental investigations of the magnetic dead layer in 7.6 nm thick film of La0.7Sr0.3MnO3 (LSMO) are reported. The dc magnetization (M) measurements for a sample cooled to T = 5 K in applied field H = 0 reveal the presence of negative remanent magnetization (NRM) in the M vs. H (magnetic field) measurements as well as in the M vs. T measurements in H = 50 Oe and 100 Oe. The M vs. T data in ZFC (zero-field-cooled) and FC (field-cooled) protocols are used to determine the blocking temperature TB in different H. Isothermal hysteresis loops at different T are used to determine the temperature dependence of saturation magnetization (M-S), remanence (M-R) and coercivity HC. The M-S vs. T data are fit to the Bloch law, M-S (T) = M-0 (1 - BT3/2), showing a good fit for T < 100 K and yielding the nearest-neighbor exchange constant J/k(B) congruent to 18 K. The variations of T-B vs. H and HC vs. T are well described by the model often used for randomly oriented magnetic nanoparticles with magnetic domain diameter approximate to 9 nm present in the dead-layer of thickness d = 1.4 nm. Finally, the data available from literature on the thickness (D) variation of Curie temperature (T-C) and M-S of LSMO films grown under 200, 150, and 0.38 mTorr pressures of O-2 are analyzed in terms of the finite-size scaling, with M-S vs. D data fit to M-S (D) = M-S(b)(1-d/D) yielding the dead layer thickness d = 1.1 nm, 1.4 nm and 2.4 nm respectively. Brief discussion on the significance of these results is presented. (c) 2018 Author(s).