Studies On Ferroic Properties Of Niobate And Ferrite

Magnetic and ferroelectric materials have attracted constant research interests for decadessince they have important applications in industry daily life. Multiferroic materials are thematerials which both have ferromagnetic and ferroelectric, and even ferroelastic. Themultiferroic materials have the characteristic of magneto-electric coupling which the polarizationcan be switched under the applied magnetic field, and also magnetization can be switched underthe applied electric field. The research of multiferroic materials is considered as a broad newfield for condensed matter physics and material science which contain abundant research area formaterial science and physics research. Multiferroic materials is national focus, and havebeen assessed as one of the most remarkable science in focus by "Science" magazine in2008.The current single-phase multiferroic materials have shortcomings in the actual production andapplication, the preparation of new single-phase multiferroic materials, as well as the newferroelectric and ferromagnetic principles of coexistence are still the focus.The ferroelectric (FE) niobates, with their relatively large spontaneous polarization (Ps)values and good piezoelectric performance which due to the satisfaction of d0rule for Nb5+ion,have become very important in applications for laser technologies, holographic techniques,integrated optics, surface acoustic wave devices, and high frequency telecommunication signalprocessing techniques. In addition, a large saturation polarization can be induced in AgNbO3under a very high external electric field, which has the commercial prospects, but thepolarization mechanism of ferroelectric is still an unresolved issue, and we have also noticed thatthere are very few low temperature studies for AgNbO3, it is still a challenge.The development of ferrite is closely connected with some foundation discipline asmagnetism, solid physics, chemistry, radio and electronics. New application areas are appearingwhen they promote each other. Rare earth iron garnets with narrow ferromagnetic resonance linewidths, very low hysteresis losses, and excellent dielectric properties have been widely appliedin microwave devices in a wide range of frequencies and typically employed as magneticrecording media. Researcher focus on the magnetic properties of garnet ferrite, but the electric properties need further research.Ferrite’s structure depends on its physical and chemical property. New structure shows goodnew character on multiferroic or the coexistence of high spin or the magneto optical properties.Combination and research for new ferrite material still are remarkably compelling.The motivation of this dissertation is to research the ferroelectricity and magnetic ofniobate and ferrite.1. The AgNbO3has been synthesized by mild hydrothermal method, the cryogenicpolarization state of AgNbO3has been researched by the dielectric, pyroelectric, thermalanalysis and P–E hysteresis loop etc. The research allows us to reveal a new ferroelectricphase in AgNbO3at low temperature which is mainly associated with the alignment of theoff-center displacements of Ag.2. The Nd3Fe5O12has been synthesized by mild hydrothermal method, the polarization state ofNd3Fe5O12has been researched by the dielectric, pyroelectric，Magnetic dielectric and P–Epolarization etc. Characterized Nd3Fe5O12by ferromagnetic resonance linewidthmeasurements. The research suggests that Nd3Fe5O12has a narrow ferromagnetic resonancelinewidth， and Nd3Fe5O12is the single-phase multiferroic material, and has strongmagneto-electric coupling effect.3. The K—2Fe4O7（P31m）has been synthesized by mild hydrothermal method, and characterizedby XRD、EDS、SEM、VSM、SQUID、Mossbauer and single crystal structure analysis. Theresearch suggests that K2Fe4O7is weak ferromagnetic material, and LS-HS transition of Fe3+occurs in this sample.