| Colossal magnetoresistive manganese oxides have been extensively studied by researchers because of their high spin polarization rates and large magnetoresistance effects near Curie temperature(Tc).In addition,there are polyphase coexistence and competition in the Poromagnetic Manganese Oxide,which makes these materials responsive to external conditions such as electric field,magnetic field,light and so on.Therefore,in this paper,we studied the effect of magnetic field and light(? = 405nm)on the magnetic field and the electrical properties by using the La1-xCaxMn O3 as the research object.The main research contents are as follows:1.La1-xCaxMn O3(x=0.10,0.15,0.2,0.3)and La0.7Ca0.3MnO3/Si heterojunction films were prepared by sol-gel method,and the structures and morphology of La1-xCaxMnO3 were characterized respectively.The XRD results show that La1-xCaxMn O3(x=0.10,0.15,0.2,0.3)and La0.7Ca0.3Mn O3/Si heterojunction films are orthogonally symmetric structures.The SEM results show th at the bulk and thin film samples are dense,the surface is flat without pores,the grain size is uniform and the grain boundary is clear.2.Electromagnetic transport properties and photoelectric properties of La1-xCaxMn O3(x=0.10,0.15,0.2,0.3)bulk samples were investigated.the electrical properties characterization(R-T curve and I-V curve)and magnetic transport characteristics(M-T curve and M-H curve)of the La1-xCaxMn O3(x=0.10,0.15,0.20,0.30)samples were systematically tested and characterized by multi-function vibrating magnetometer as test platform.The magnetic test results show that the magnetic state of La1-xCaxMnO3(x=0.10,0.15,0.20,0.30)has a paramagnetic to ferromagnetic transition with the decrease of temperature(300K-50K),and the paramagnetic-ferromagnetic transition temperature is obviously increased with the increasing of doping amount of Ca.From the change of the resistance of La1-xCaxMn O3 with temperature,it can be seen that La1-xCaxMn O3 sample undergoes a significant change the phase from insulator to metal.The electrical properties of the La1-xCaxMn O3 bulk sample under light conditions show that the resistance of the La1-xCaxMn O3 bulk sample increases in the low temperature region and decreases in the high temperature region as the laser intensity increases.From the results of the current voltage curve(I-V curve)of the La1-xCaxMn O3 sample,the I-V curve of the La1-xCaxMnO3 sample is changed and the open-circuit voltage is generated,which means,the photovoltaic effect is generated.The further study of La1-xCaxMnO3 sample open-circuit voltage with temperature curve shows that the change of the open circuit voltage of La1-xCaxMnO3 sample is related to the change of the magnetic state and the resistance of the La1-xCaxMnO3 sample with the decrease of the temperature after the addition of light.However,the microscopic mechanism of the effect still needs further study.3.The La0.7Ca0.3MnO3/Si heterojunction was prepared by La0.7Ca0.3Mn O3 sample which has high phase transition temperature.The transport characteristics and photovoltaic effects of the manganese oxide heterojunction was tested by the multi-functional magnetometer Vaserlab test system.The magnetic transport(M-T and M-H)curves of different concentrations and layers show that the magnetic properties of the sample are very strong.The magnetization reaches saturation at 1000 Oe and the coercivity of the 10 and 13 film samples is 364 Oe and 352 Oe,respectively.In the magnetic field and laser conditions,the electrical properties characterization of La0.7Ca0.3MnO3/Si heterojunction samples with different concentrations and layers shows that with the increase of the magnetic field strength,the resistance of the sample decreases;with the increase of the laser intensity,the resistance of the sample hardly changes.The analysis of the I-V curve of the magnetic field and the laser at different temperatures shows that magnetic field strength and laser intensity both have obvious effect on the photoelectric effect of the sample,but the influence of the photo-generated voltage is different(see 4.4),which means that the magnetic field and the laser have different influence on the magnetic ground state of the sample. |
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