Effects of Oxygen Modification on the Structural and Magnetic Properties of Highly Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films

Abstract

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 ...

Double-Exchange Bias Modulation under Horizontal and Perpendicular Field Directions by 3D Nanocomposite Design

“…Generally, the magnetic response of LSMO is highly dependent on the double exchange of the e g hopping from Mn 3+ to Mn 4+ , and the modification of the angle or length of the Mn–O–Mn bond caused by strain can correspondingly tailor its magnetic performance. It was reported that IP compressive strain results in higher T c because of the reduced Mn–O–Mn bond length, while oppositely, tensile strain leads to lower T c . , In addition, defects such as oxygen vacancies could break the exchange mechanism and increase the spin disorder and thus reduce T c . Therefore, the mechanism of the increased T c in this case is quite complicated as both the strain state and the interfacial defects could contribute to the magnetic properties.…”

Metal–Insulator Transition via Ion Irradiation in Epitaxial La0.7Sr0.3MnO3−δ Thin Films

“…The pristine state exhibits ferromagnetic behavior with a high Curie temperature above 300 K. The result is in good agreement with the domination of the double-exchange mechanism among the d-orbital magnetic ions (Mn 3þ and Mn 4þ ) for this stoichiometry. [30][31][32] After implantation, we expect that the nominal manganese valence is reduced due to the introduction of defects (primarily oxygen vacancies), in which the fraction of Mn 3þ ions becomes more abundant. As a result, a Mn 3þ -O-Mn 3þ combination is prevalent among most manganese centers in the system and a strong superexchange coupling starts to take over.…”

Диффузия кислорода в La-=SUB=-0.8-=/SUB=-Sr-=SUB=-0.2-=/SUB=-MnO-=SUB=-3-delta-=/SUB=- пленках разной толщины на NdGaO-=SUB=-3-=/SUB=--подложках

“…Технология получения высококачественных пленок на основе легированных манганитов с кислородным содержанием (КС), близким к стехиометрическому составу, как правило, включает термообработку пленочных структур в кислородосодержащей газовой среде. Обеспечить стехиометрический состав по кислороду непосредственно в процессе роста пленок (in situ) довольно сложно [1][2][3]. Процедура термообработки уже готовой пленки позволяет изменять КС пленочного материала и, таким образом, корректировать электрические и магнитные характеристики объекта, например, обеспечивать максимальное значение температурного коэффициента сопротивления в заданном интервале температур.…”