Effect Of Different Crystalline States On The Electrical And Magnetic Properties Of La_1-xSr_xMnO₃ Thin Films

Perovskite manganese oxide has been the focus of research in condensed matter physics due to it exhibits many novel physical properties such as colossal magnetoresistance,exchange bias,and resistance switching characteristics.It can obviously broaden the application range of such devices and make transparent glass devices to be the focus of the development of modern electronics.This paper focuses on the research of the resistance switch and magnetoresistance characteristic of La0.67Sr0.33MnO3?LSMO?film,and the research on the exchange bias effect of La0.5Sr0.5MnO3with phase separation.The research contents of this paper mainly include the following three parts:?1?Resistance switching characteristics of different crystalline La0.67Sr0.33MnO3filmsOn the FTO substrate,two different crystalline LSMO films were prepared by sol-gel method,respectively defined as LSMO-1 and LSMO-2.The XRD and EDS spectra show that the LSMO-1 thin film is an amorphous film,while the LSMO-2 is a single-phase polycrystalline film.The microscopic morphology of the two samples observed by AFM and SEM shows that the surface of LSMO-1 has a lot of particle clusters in together,no grain was observed,and with 250nm thickness.The surface distribution of LSMO-2 film are relatively uniform,the density and clear grain boundary with the thickness of 290nm.Two kinds of films were evaporated on the top electrode to form Ag/LSMO/FTO devices.A study of the translucency of these two devices shows that the light transmission of the LSMO-1 device is 67%,while the LSMO-2 is a completely opaque device.A study of the resistive switching characteristics of these two devices shows that the resistance of the LSMO-1 device has reached 10⁶ to 10⁸?,which is nearly 4 orders of magnitude higher than that of the LSMO-2 device,but its high/low resistance ratios have been achieved 10²,far higher than the resistance ratio of LSMO-2 devices,and has good retention and fatigue.A study of the resistance switching mechanism of these two devices found that the resistive effect of LSMO-1 devices is the conductive filament mechanism,and the resistance of the LSMO-2 device is mainly due to the role of the Schottky barrier at the interface.?2?Effect of annealing temperature on magnetic properties of La0.67Sr0.33MnO3thin filmsThe sol-gel method was also used to prepare different samples.By measuring the M-H and M-T curves of the two films,the amorphous 500°C film was paramagnetism.The crystalline 600°C and 650°C films exhibit ferromagnetism.Whether it is a crystalline film or an amorphous film,they are not spin glass states.As the preparation temperature increases,the degree of crystallinity increases and oxygen vacancies gradually decrease.According to the principle of valence balance,oxygen ions enter the crystal lattice and increase the proportion of Mn⁴⁺/Mn³⁺.Therefore,as the temperature rises,disorder in the internal arrangement becomes orderly,resulting in smaller resistance.The magnetoresistance of each sample was calculated.The magnetoresistance of the sample at 500°C is a positive magnetoresistance?about 30%?.Since it is an amorphous sample,its mechanism is not a category that double exchange can explain.The interface is explained with wear,and the magnetoresistance of both samples at 600°C and 650°C is a negative magnetoresistance?-3.5%and-25%?,and the magnetoresistance gradually increases as the temperature increases.Mainly due to the increase in temperature,the double exchange effect becomes stronger leading to a decrease in the resistance and a larger magnetoresistance.?3?Study on the exchange bias of La0.5Sr0.5MnO3A single phase polycrystalline La0.5Sr0.5MnO3film was prepared on a FTO substrate by a sol-gel method.Observation of the surface microstructure by SEM revealed that the grain size was in the range of 5.3²2.1nm,and its thickness is 163nm.The magnetic measurement of the film found that the horizontal exchange bias can reach 255Oe in the field of 500Oe,and the measurement of the training effect of the film finally proves that the film has higher stability.The exchange bias of the sample increases gradually as the temperature decreasing,abruptly increases rapidly when the blocking temperature reaches approximately 68K,and the bias is exchanged as the temperature decreases.Due to the coexistence of FM and AFM at low temperatures,the coupling of the FM/AFM interface leads to the generation of exchange bias,and the lower the temperature,the stronger the interfacial coupling of the film.