Preparation, Microstructure, Electrical And Magnetic Properties Of YMnO₃Based Multiferroic Ceramics

Multiferroic materials have recently attracted significant research interests inmaterials science owing to their integration of ferroelectricity and ferromagnetism,where the magnetoelectric coupling could enable the mutual control of electric andmagnetic properties through one on the other. Hexagonal YMnO3is one of the mostimportant multiferroic materials with a Curie temperature (TC) of900K and a Neeltemperature (TN) of70K.In this study, microwave-assisted sol-gel method and low-temperature solid statereaction method are employed to synthesize YMnO3nanoparticles. The as-preparednanoparticles have been investigated with X-ray Diffraction (XRD), field emissionscanning electron microscopy (FSEM) and transmission electron microscopy (TEM).The results demonstrate that YMnO3nanoparticles synthesized by the low-temperaturesolid state reaction method have smaller average particle size than the ones by thesol-gel method. The simplified process by the solid reaction method, as well as thesmaller nanoparticle size, is more advantageous for a following preparation of densebulk ceramics.Low-temperature and conventional solid reaction methods are used to prepareYMn0.8Fe0.2O3powders. The magnetic properties of corresponding ceramics bydifferent methods are investigated and compared. The dense YMn0.8Fe0.2O3ceramicsynthesized by low-temperature solid reaction method is further processed in oxygenand nitrogen atmosphere,respectively. The effect of oxygen vacancy concentration onceramic microstructure and magnetic properties is studied. The results show that thedifferent preparation methods have large effects on the microstructure and magneticproperty of the ceramics.In addition,ceramics annealed in O2and N2atmosphere show alarge decrease of magnetic transition temperature and different distribution of valencestates of magnetic ions.The N2-annealed ceramic shows the competition between FMand AFM interactions when temperature is lower than its TN,which indicates that theceramic favor the spin-glass phase.Dense Y1-xCexMn0.8Fe0.2O3(x=0.05，0.1) and Y1-xZrxMn0.8Fe0.2O3(x=0.05，0.1)solid solution ceramics are prepared, where the Ce4+、Zr4+with high-valence states (Ce4+and Zr4+) are used for the partial substitution for Y3+in YMn0.8Fe0.2O3samples. This study investigates the effect of A-site substitution with high-valance ions on themicrostructure and properties of YMn0.8Fe0.2O3ceramic. The results show that：Thedielectric loss decreases and the electrical resistivity increases as the doping amount ofCe4+、Zr4+is0.05. The different distribution of valence states of magnetic ions leads tothe magnetic transition temperature graudually decreases with increased Ce4+、Zr4+doping concentration.