2, Department of Mechanical & Aerospace Engineering, West Virginia University,, Morgantown, West Virginia, United States
As fabrication technology pushes magnetic structures into nanoscale dimensions, understanding the magnetization processes of these structures is of fundamental interest, and the key to future applications in spin-caloritronics, high density non-volatile magnetoresistive random memory (MRAM), spintronic and other multifunctional devices. Manganite perovskite La0.7Sr0.3MnO3 (LSMO) has been extensively investigated in the last decade due to its colossal magnetoresistance, high spin polarization, and above room temperature Curie temperature (Tc) which make this material very promising for various applications. La0.7Sr0.3MnO3 (LSMO) thin films were fabricated by optimized pulsed laser deposition on (100) SrTiO3 single crystal substrates in a different oxygen growth pressure varied from 50 mTorr to 250 mTorr. The quality of growth and crystallinity of the films were monitored in situ with RHEED. The RHEED pattern clearly showed two-dimensional spots with 2D streaks for the films grown at 100 and 150 mTorr. These films were confirmed to be single crystalline with atomically flat surfaces, whereas single crystalline films with rough three dimensional surfaces were found for the LSMO films grown in other oxygen pressures. The thickness of these films was estimated from RHEED oscillations and X-ray reflectivity (XRR) measurements. The θ-2θ large angle x-ray scans showed only diffraction peaks from the substrate and (00l) pseudocubic reflections from LSMO, confirming that these films are highly oriented. The atomic force micrographs revealed that the surfaces of all the thin films are observed to be smooth and homogeneous, free of microcracks, pores or holes with average surface roughness below 1 nm. The films grown at 100 mTorr exhibits lowest surface roughness. All the thin films exhibit excellent saturated ferromagnetic behavior with large magnetization. Negative remanent magnetization (NRM) in these thin films have been observed in zero-field-cooled magnetization vs. temperature measurements with low measurement fields. Thin films grown at 150 mTorr possesses highest saturation magnetization (Ms) of ~540 emu/cm3 at 5 K among all and showed Ferromagnetic to Paramagnetic transition around 335 (+/-5) K. Detailed studies on structural, morphological and magnetic properties of these thin films will be discussed in the meeting. We acknowledge WVU Shared Research Facilities and funding support from NSF (DMR-1608656) and DOE (DE-SC0016176) for the growth, and characterization of these films.