Preparation Of La_1-xCa_xMnO₃:Ag_0.2 Thin Films By Ultraviolet Pulsed Laser Deposition Technology And Electrical And Magnetic Properties Can Study

As a strongly correlated oxide,La_1-xCa_xMnO₃:Ag_0.2 has rich physical properties,and it has giant magnetoresistance effect and metal-insulator transition behavior.It can be applied to the production of photoelectric fast devices,bolometers,high-density magnetic storage heads,refrigerators,and infrared detectors.So,it has great research and application value.In this paper,La_1-xCa_xMnO₃:Ag_0.2?x=0.28,0.285,0.30,0.33?ceramic polycrystalline samples were prepared by sol-gel method,and then the effect of different Ca content on the performance of polycrystalline target was investigated.According to the previous experiments,the addition of Ag can significantly improve the electrical properties of polycrystalline e samples.Polycrystalline samples with excellent properties are used as targets for the preparation of thin film materials.We use pulsed laser deposition?PLD?to prepare thin film materials.In this paper,the effects of coating technology on the electrical and magnetic properties of thin films were studied by adjusting the coating process parameters such as laser energy,growth temperature,growth oxygen pressure,annealing temperature,annealing oxygen pressure,substrate material,and laser frequency.The X-ray diffraction?XRD?,scanning electron microscopy?SEM?,and atomic force microscopy?AFM?were used to test the phase structure and surface morphology of thin film samples.We use four probe testing equipment?R-T?and superconducting quantum interferometer?SQUID?to test the changes of electrical and magnetic values with the temperature.The analysis of the test results shows that the change of Ca doping amount will have a significant effect on the properties of polycrystalline samples.With the increase of Ca content,the T_p value of the sample increases,the resistivity decreases,and the TCR decreases.Through the analysis?-T of samples,the change of Ca content is mainly responsible for the change of the ratio between Mn⁴⁺/Mn³⁺.Meanwhile,the average ionic radius of A will also be affected,which will further affect the performance of samples.The film material was prepared by PLD with different coating process parameters.The XRD pattern shows that all the film samples grew along the c orientation.Changing the coating process will have a significant effect on the crystalline quality of the film.At the time,the presence of stress will cause the diffraction peak to have a certain degree of angular shift.Through the SEM test images,We can see that the thickness of the thin films prepared by PLD with different laser energy are different.Meanwhile,the change of energy will affect the deposition and migration of plume particles.It can be seen from the AFM test image that the films all exhibit three-dimensional island growth.As the coating process parameters change to a certain extent,the film changes from the island growth to the layered growth.The R-T test shows that the films material exhibit the metal-insulator transition behavior with the change of temperature.During the process parameter changes,the resistivity and the T_p of the thin film will change.This is mainly due to the effect of Mn⁴⁺-O-Mn³⁺double switching.The M-T test results show that the film samples all exhibit a ferromagnetic-paramagnetic transition.Due to changes in the coating process parameters,the saturation susceptibility and curie temperature?T_c?of the film show different changes.This is because the magnetic spin order of the film is affected during the film preparation.By comparing the properties of the films,the best electrical and magnetic properties of the films can be prepared at:laser energy 300 mJ,growth oxygen pressure 100 Pa,growth temperature 790°C,annealing oxygen pressure 10⁵ Pa,annealing temperature 900°C,and laser frequency 5 Hz.It can be used as a reference parameter for the preparation of Perovskite Thin Film Materials in the later period.