Studies On Magnetoelectric Coupling And Other Behaviors Of Materials With Perovskite Structure

ABO3with perovskite structure is a kind of multifunctional materials and It has been attracted much attention in recent years because of the good performances of ferroelectric, magnetism and gas-sensing. The macroscopic properties are not independent of each other. There exists a close relationship between them.The coupling of ferroelectric and magnetism is always be found in multiferroic, in which ferromagnetism (anti-ferromagnetism) and ferroelectricity (anti-ferroelectricity) can coexist. Multiferroic is rare because of the difficulty of coexisting of ferroelectric and magnetism. In spite of it, several multiferroic have been found in the material of rare-earth RFeO3with perovskite structure. It is interesting to find ferroelectric in the family of centrosymmetric RFeO3with a non-polar group point of Pbnm. It is generally accepted that the improper ferroelectricity is originated from the spin configurations which are related to the canted spins of R and Fe ions. Therefore, there exists a potential magneto-electric effect in the RFeO3whose ferroelectricity is induced by this canted spin structure and the magneto-electric coupling of RFeO3with perovskite structure has become a hot spot in research. However, most of magnetoelectric coupling of RFeO3are found at low temperature and are not conducive to the paractical application. Here we present room-temperature magnetoelectric coupling in NdFeO3and Nd1-xSmxFeO3(x=0.2,0.4) in the system of RFeO3.The electrical properties can be influenced by the magnetism in the perovskite-structure material, but not limited to. There also exists a close relationship between the gas-sensing property and the electrical performance. As we all know, the gas-sensing property of perovskite rare-earth oxides can be measured though the change of the dielectric constant and the conductance, however, the mechanism is still not clear. We studied the gas-sensing property through XPS and found that it was Fe ions that dominated the gas-sensing property and it also had an influence on the electrical properties. The main conclusions of our work are as follows:1. We measured M-T curve of perovskite-structrue NdFeO3below room temperature and found several anomalies, which were accompanied by the change of dielectric constant, especially in the temperature range of spin reorientation. We also measured M-H curves at different temperatures and the results showed a small coercivity in the temperature range of spin reorientation. In short, there exists an obvious magnetodielectric effect in NdFeO3below room temperature.2. We demonstrated ferromagnetism of NdFeO3at room temperature and the antiferromagneic transition point at680K through the curves of M-H and M-T respectively. We observed the electric field controlled magnetization under a field of14kOe. The magnetization decreased under a square wave electric fields slowly and abruptly when E//H and E⊥H respectively. Besides, we observed the room-temperature magnetodielectric effect through the curves of the frequency dependence of dielectric constant under various magnetic fields. We attributed the relaxation of dielectric constant which we observed on the curve of ε-T to the small polaronic hopping among various valences of Fe ions.3. In the single phase sample of Ndo.8Smo.2FeO3, we observed the room-temperature magnetodielectric effect. The curves of magnetization as a function of magnetic filed under/without7.5kV/cm electric field parallel to the magnetic field were measured at room temperature and we observed an increase of magnetization when the electric field was introduced. We also found the electrical field controlled magnetization under the square wave electric fields parallel to the magnetic field H at room temperature. In the single phase sample of Ndo.6Smo.4Fe03, we observed the room-temperature magnetodielectric effect through the curves of dielectric constant as a function of frequency under various magnetic fields. Being different from NdFeO3and Ndo.8Smo.2Fe03, the time dependence of magnetization decreased abruptly when E//H under the square wave electric fields, Above all, we observed the magnetoelectric coupling at room temperature in the samples mentioned above.4. We also investigated the close relationship between the electrical property and the gas-sensing of perovskite-structure La1-xBaxFeO3(x=0,0.1,0.2,0.3). Through the analysis of XPS, we found that the ratio of Fe4+/Fe3+had an inverse correlation with the resistance of La1-xBaxFeO3(x=0,0.1,0.2,0.3), moreover, the ratio of Fe4+/Fe3+is in agreement with the gas-sensing property. Therefore, the Fe ions act as the role of bridge connecting the gas-sensing property and the electric properties in the perovskite-structrue materials. In multifunctional materials with perovskite structure, There exists a close relationship between the electrical property, magnetic performance and the gas-sensing property.