a strong semi-metallic ferromagnet having robust spin polarization and magnetic transition temperature (T c) well above 300 K, has attracted significant attention as a possible candidate for a wide range of memory, spintronic, and multifunctional devices. Since varying the oxygen partial pressure during growth is likely to change the structural and other physical functionalities of La 0.7 Sr 0.3 MnO 3 (LSMO) films, here we report detailed investigations on structure, along with magnetic behavior of LSMO films with same thickness (~30 nm) but synthesized at various oxygen partial pressures: 10, 30, 50, 100, 150, 200 and 250 mTorr. The observation of only (00 l) reflections without any secondary peaks in the XRD patterns confirms the high-quality synthesis of the above-mentioned films. Surface morphology of the films reveals that these films are very smooth with low roughness, the thin films synthesized at 150 mTorr having the lowest average roughness. The increasing of magnetic T c and sharpness of the magnetic phase transitions with increasing oxygen growth pressure suggests that by decreasing the oxygen growth pressure leads to oxygen deficiencies in grown films which induce oxygen inhomogeneity. Thin films grown at 150 mTorr exhibits the highest magnetization with T C = 340 K as these thin films possess the lowest roughness and might exhibit lowest oxygen vacancies and defects. Interpretation and significance of these results in the 30 nm LSMO thin films prepared at different oxygen growth pressures are also presented, along with the existence and growth pressure dependence of negative remanent magnetization (NRM) of the above-mentioned thin films. The miniaturization of devices to increase speed and reduce the cost of materials is an ongoing need for many current and potential magnetic technologies such as spintronics, highly dense non-volatile memory, spin-caloritronics, and different multifunctional micro and nanoscale devices 1-5. Among important materials for device applications are room temperature ferromagnetic oxides such as the manganites, La 1−x Sr x MnO 3 , since their properties can be tuned using a number of degrees of freedom including charge, spin, orbital, and magnetic ordering phenomena 6,7. They are also excellent candidates for novel engineered nanostructures as they exhibit colossal magnetoresistance (CMR) effect which has been used for different multifunctional applications 8-10. La 1− x Sr x MnO 3 also shows CMR phenomena under smaller external magnetic fields compared to the other manganites and strongly correlated materials 11,12. Among the La 1−x Sr x MnO 3 manganites, the optimized stoichiometry La 0.7 Sr 0.3 MnO 3 (LSMO) is one of the most prominent members with outstanding magnetic and magneto-transport properties. Compared to other typical magnetic oxides, LSMO exhibits semi-metallic behavior, outstanding ferromagnetism, high Fermi-level spin polarization, with a bulk magnetic ordering temperature, T C (= 370 K) well above room temperature 13,14. Also, the spin polarization of LSMO ...

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 (MS), remanence (MR) and coercivity HC. The MS vs. T data are fit to the Bloch law, MS (T) = M0 (1 – BT 3/2), showing a good fit for T < 100 K and yielding the nearest-neighbor exchange constant J/kB ≅ 18 K. The variations of TB vs. H and HC vs. T are well described by the model often used for randomly oriented magnetic nanoparticles with magnetic domain diameter ≈ 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 (TC) and MS of LSMO films grown under 200, 150, and 0.38 mTorr pressures of O2 are analyzed in terms of the finite-size scaling, with MS vs. D data fit to MS (D) = MS(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.

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The observation of inverted magnetic hysteresis loops and negative magnetic remanence (NRM) in a 7.6 nm thin film of LaSrMnO grown on SrTiO substrates is reported. The film was grown employing pulsed laser deposition and characterized by reflection high-energy electron diffraction during growth and using x-ray reflectivity measurements post-growth. Magnetic properties of the film were measured from 5 K to 400 K under both the field-cooled (FC) and zero-field-cooled (ZFC) conditions. The observed results of inverted magnetic hysteresis loops and NRM are interpreted in terms of the co-existence of a magnetically inhomogeneous region consisting of superparamagnetic spin clusters with a blocking temperature T =  240 K and the ferromagnetic state with an ordering temperature T =  290 K. Hysteresis loop inversion is observed in the temperature region of T < T < T whereas NRM appears in the mixed superparamagnetic and ferromagnetic states for T< T down to 5 K. These observations of hysteresis loop inversion and NRM are related to the magneto-static interaction between the superparamagnetic and ferromagnetic phases leading to anti-alignment of spin of both magnetic phases with respect to each other.