Microstructure And Electronic Property Modulation Of La_0.8Sr_0.2MnO₃ Films

Perovskite manganese oxides have been studied intensively due to their rich physical properties,such as magnetic,multiferroic,colossal magnetoresistance,and transport properties,which offer possible applications in electronic devices.Novel approaches,such as chemical doping,oxygen vacancy,and misfit strain,have been proposed to tune the crystalline structure and electronic properties in perovskite manganites.The oxide films with ferromagnetic insulator phase,which simultaneously possess both spin polarization and insulation,are central to the integration of versatile spintronic devices.However,the study of promising high-temperature ferromagnetic insulators in perovskite manganese films is still at the infant stage,comparing with the extensively explored bulk materials.In this paper,La_0.8Sr_0.2MnO₃ thin films are taken as the research object,to modulate the microstructures and electronic properties by means of oxygen vacancy,misfit strain and hydrogen plasma treatment.A weak ferromagnetic phase,accompanied with a topotactic metal-insulator transition has been obtained in strained La_0.8Sr_0.2MnO₃ films,through the hydrogen plasma treatment,which provides new direction to explore high Curie temperature magnetic insulators.The main findings of this study are listed as follows:La_0.8Sr_0.2MnO₃ films were prepared by pulsed-laser deposition.High-quality La_0.8Sr_0.2MnO₃ thin films were obtained by optimizing the deposition parameters,such as oxygen pressures,laser energy,temperature,substrates and film thickness.Firstly,the magnetic and electrical properties of La_0.8Sr_0.2MnO₃ thin films clamped by different?001?-oriented substrates were systematically.It was observed that properly small misfit strains?-1.35%to+0.26%?could obviously improve the Curie temperature of?001?-oriented La_0.8Sr_0.2MnO₃ films with prominent saturated magnetization?up to 576emu/cm³?.An insulating phase with a wide temperature range?10–400 K?has been achieved for the largely strained La_0.8Sr_0.2MnO₃ films.These results could inspire a new direction in developing high-temperature magnetic insulators,which are beneficial to applications of manganite films as promising spintronic devices.Secondly,La_0.8Sr_0.2MnO₃ thin films were deposited on substrates with different orientations?i.e.,?001?,?110?and?111??to control the microstructures and physical properties.The metal-insulator transition was found for La_0.8Sr_0.2MnO₃ thin films deposited on?111?LaAlO₃ substrate,with obviously enhanced saturation magnetization?143 emu/cm³?and Curie temperature?297 K?.Finally,a perovskite-brownmillerite phase transition was found in La_0.8Sr_0.2MnO₃ thin films via hydrogen plasma treatment.A metal-insulator transition and high Curie temperature weak ferromagnetism were obtained for the hydrogenated La_0.8Sr_0.2MnO₃ thin films.This provides a feasible method for the exploration of high temperature ferromagnetic insulators.In summary,we have obtained the structure-induced high-temperature metal-insulator transition in La_0.8Sr_0.2MnO₃ films by means of large misfit strain.Meanwhile,we have obtained a weak ferromagnetic insulator with relative high Curie temperature in the plasma driven phase transition of La_0.8Sr_0.2MnO₃ films.This study provides a new method of thinking for the research of high temperature magnetic insulators.