The Effect In Microstructure For Magnetic And Electrical Properties Of Rare Earth Chromium Oxides

People pay more and more attention to the rare earth chromium oxide which has the novel physical characteristics,because it has a broad application prospect in the solar cell,colossal magnetoresistance,multiferroic memory and photosensitive sensor,and other fields.Therefore,it is very meaningful to explore the influence of microstructure on the performance of the system and expect to find the possible intrinsic relationship between them.In this paper,rare earth chromium oxide RCrO₃?R=La,Nd,Sm,Eu,Gd,Dy,Ho,Er,Yb,?is taken as the research object,and the basic physical properties of magnetic,dielectric and magnetic dielectric are taken as the starting point.The microstructure and crystal structure of polycrystalline samples were studied systematically.The polycrystalline samples of RCrO₃ in this paper were prepared by conventional solid state.The crystal structure,microstructure,magnetic and dielectric properties and resistance of the system samples were analyzed by X-ray powder diffraction,field emission scanning electron microscopy,comprehensive physical property testing system,precision impedance analyzer and high resistance meter,respectively.By refining the XRD data of the whole system sample,it is verified that there is an abnormality in the cell parameter b when IR=1.11?.Combined with the changes of cell parameters and bond length and bond angle,we have a clear understanding of the process of crystal structure distortion.We believe that the tolerance of the whole cell reaches its limit when the rare earth ion radius reaches IR=1.11?(Gd³⁺).Therefore,the original crystal structure cannot be maintained if the volume of crystal cell continues to shrink.In order to adapt to the trend of further reduction of the whole crystal cell,the octahedrons will tend to increase torsion,and the bond angle of O₁-Cr-O₂₁1 within the octahedrons began to gradually decrease,and greater degree of distortion occurred between the octahedrons and within the octahedrons.For the novel magnetic properties of this system.We believe that the sample whether have magnetization reversal in field-cooling?FC?mode was determined by the magnetic moment between the Cr³⁺canted-antiferromagnetism and R³⁺magnetic moment tend to be ferromagnetic or anti-ferromagnetic.And this is related to the H_I value of the inner field obtained by fitting.The negative magnetization in the zero-filed-cooling?ZFC?mode is attributed to the remaining negative trapped field?TF?of the superconducting coil and the interaction between particles.Dielectric relaxation was observed in the dielectric temperature spectra of the samples.By combining the microstructure and impedance spectrum analysis of the samples,we believe that the samples in this system have the contribution of different components?grain,grain boundary?.In addition,according to the analysis of the change rate of dielectric loss with frequency in EuCrO₃ sample,we the dielectric relaxation phenomenon in this system is a kind of Maxwell-Wagner?M-W?relaxation.By combining resistance and magnetization data at low temperature the,we consider the magnetodielectric?MD?effect existing in the sample which without the magnetic structure transformation at low temperature is simply due to the resistance of any layer within the sample was changed by magnetic field.Such as:EuCrO₃,DyCrO₃,HoCrO₃,YbCrO₃.However,such as NdCrO₃,SmCrO₃ and GdCrO₃,the sample which have magnetic structure transformation at low temperature,the MD effect is not only caused by the above reasons,but also the intrinsic magnetoelectric coupling effect caused by ferroelectric phase transformation induced by magnetic structure.