Hard Template Synthesis And Magnetic Properties Of Perovskite Maganese Nanowire Bundles

perovskite maganeses are strongly correlated electronic materials.Although the effect of double exchange and Jahn-Teller effect could explain some phenomenons in the past study of experiment and theories,there still remain some questions or phenomenons need to be clarified such as some special magnetic transition behaviors.Therefore,scientists used a variety of theoretical models to explain phase transition by simple simulation of the real physical system.Recent developments in nanomaterials confirm perovskite maganeses contain unique physical and chemical properties.In this subjects,we synthesised perovskite maganeses nanobundles by hard templat,then studied their magnetic properties and calculated critical parameters for describing critical behaviors.The main studies includes:（1）Nanobundles LaMn O3 with ordered arrangement were synthesized by hard template method and the mesoporous silica dioxide SBA-15 as the template.The effect of calcined temperature,template pore’s structure on the obtained samples’ specific surface was researched.In the temperature region of 650 ℃-700 ℃,the higher of calcined temperature,the larger of the specific surface.Extra-high temperature will destroy the stability of template then affect the structure of obtained LaMn O3 samples,result in the less of samples’ surface.Under same calcined temperature 700 ℃,the larger of the pore diameter of template,the higher of the samples’ specific surface.The magnetic of nanowires LaMnO₃ can be influenced by uncompensated surface and interface spins moments.The larger of specific surface,the more of the surface uncompensated spin moments,the stronger of ferromagnetic.（2）Highly ordered La_0.5Ca_0.5MnO₃ nanowires bundles were synthesized using mesoporous SBA-15 silica as the hard template.The magnetic properties and critical behaviors of the ferromagnetic-paramagnetic（FM-PM）phase transition of the La_0.5Ca_0.5MnO₃ nanowires bundles are investigated through isothermal magnetization methods.The calculated results show that the FM-PM transition is second order and the magnetic interaction has some deviations from the mean-field model.Though the obtained critical parameters of β=0.596±0.009,γ=1.131±0.008 and δ=2.99±0.05 follow the Widom scaling relation and the single scaling equation,the critical exponents do not obey the magnetization entropy scaling theory.The Curie temperature was comfirmed to be 238 K.These peculiar behaviors indicated that the nanometer-size effect play a significant role in the magnetic phase transition and magnetic entropy of La_0.5Ca_0.5MnO₃ nanowires bundles.（3）Highly ordered La_0.5Sr_0.5MnO₃ nanowires bundles were synthesized using mesoporous SBA-15 silica as the hard template.We investigated the critical behaviors of the perovskite La_0.5Sr_0.5MnO₃ nanobundles around the ferromagnetic-paraferromagnetic transition through critical isothermal analysis.The critical exponents β=0.93,γ=2.25 and Curie temperature Tc≈328 K were determined acccording to modified Arrott plots under a low external magnetic field of 0-0.8KOe.The availability of the parameters was proved by fulfilling the Widom scaling relation and obeying the single scaling equation.In this system,the critical exponents were determined anomalous and do not belong to any transition theories reported before.This result may be attributed to the nano-size effect and surface magnetism.