Preparation And Properties Of Single-Phase Multiferroic Material YFO₃

The single-phase multiferroic oxides are simultaneously ferromagnetic andferroelectric, and often also ferroelastic. They are to achieve rich functionality in onematerial through magnetoelectric coupling and attract now considerable attentionbecause these materials are key components for many technological applications.Both hydrothermal synthesis play an important role in the inorganic synthesischemistry, so that the materials obtained by methods mentioned above exhibit specialphysical features. Therefore, the current research involves in the chemistry, physics,and science of materials. During the hydrothermal process, the taking place ofchemical reactions leads to produce advanced oxides containing more transitionelements whose oxidation states are crucial for determining electric and magneticproperties. It is better to understand that the transition metal ions, asymmetric unit,electron spin, and structure match with ferromagnetism and ferroelectricity based oncurrent ferromagnetic and ferroelectric theories. The idea of producing new materialsalso allows new fundamental knowledge of properties of solid state to be developed.In ABO₃perovskite oxides, it is particularly difficult to simultaneously realizeferroelectric and magnetic orderings, i.e., multiferroicity, because the electronsoccupying the d shells of the transition metal ions prevent the simultaneousappearance of the two conventional orderings. Using multiferroic materials toconstruct ever smaller, multifunctional electronic devices is one of the most appealingprospects in the fields of information storage and spintronics. Consequently,researchers never stop searching for materials exhibiting multiferroic behavior via alternative mechanisms that might enable circumvention of chemical incompatibilitiesin attempts to simultaneously achieve ferroelectric and magnetic orderings.BiFeO₃is perhaps the only single-phase multiferroic material which exhibits alarge electric polarization （40μC/cm²） in a ceramic sample at room temperature, butits magnetization is now thought to be near zero. Regarding the origin offerroelectricity in BiFeO₃, it has been accepted that this arises in Bi3+with its lonepairs of electrons. Orthoferrites have been studied for decades, and until very recently,there has been no report of ferroelectricity; this is because in theory, ferroelectricitywould in fact be forbidden by their centrosymmetric Pnma/Pbnm structure. However,there is now more recent work suggesting not only low-temperature ferroelectricity inGd（Dy）FeO₃but also room-temperature ferroelectricity in SmFeO₃. In these cases, thestriction through the exchange interaction between the Gd and Fe spins in GdFeO₃,and reverse Dzyaloshinskii-Moriya interaction in SmFeO₃provided theferroelectricity.In the second chapter of the thesis, the orthoferrite YFeO₃with orthorhombicperovskite structure （Pnma） has been synthesized by mild hydrothermal method. Thetemperature-dependent magnetization and hysteresis loops indicate that, due to thesuperexchange and Dzyaloshinskii-Moriya interactions in the crystals, the Fe spinsorder antiferromagnetically at the Neel temperature655K with a weak ferromagneticmoment. The observation of saturation polarization loops at room temperature and77K provide evidence for the ferroelectric character of the polycrystalline samples. ItsCurie temperature has been obtained from the temperature dependence of the relativepermittivities and thermal analysis. We present direct experimental evidence for thesimultaneous coexistence of ferroelectricity and weak ferromagnetism in the titlecompound at room temperature. The spin reorientation occurred at about70K. Theelectric polarization detected in YFeO₃at77K is relatively small, but is comparableto the polarization of GdFeO₃at2K. As a result, the structure exhibits simultaneouslyweak ferromagnetic and ferroelectric behavior.In the third chapter of the thesis, we introduce pulsed laser deposition technique （PLD）about the preparation of oxide thin films, and its advantages. Then, we havegrown YFeO₃oxide film on the SrTiO₃（the direction of the crystal axis is100）,According to the relevant experimental, we know the crystal structure of the film,thickness and elemental composition. Finally, we have analyzed the weakferromagnetic behavior of the film.This thesis possesses the relevant characteristics of chemistry, physics andmaterials science, and introduce multiferroicity, hydrothermal Synthesis and theregular pattern of magnetoelectric. The work helps in opening a route to achievemultiferroic materials.