The Magnetic Modulation Effects On Magnetization Behaviors Of Perovskite-like Oxides With Different Magnetic Coupling System

The magnetism of transition metal compound plays a central role in the condensed matter physics. Intensive study has been carried out to breakthrough accomplishments in understanding the fundamentals since the 1950s. Magnetic filed, similar to temperature and pressure, is a kind of thermodynamic parameter which can change the internal energy of the material. It can directly interact with the charge and spin of the material, and then change the electronic structure. Thus, we can make use of the magnetic field to study the spin frustration, pinning effect and spin gap. In this thesis, we investigate the magnetic field modulation effects on the magnetization behavior of different magnetic coupling system with the distortion perovskite, perovskite and perovskite-like structure in magnetic field. The main investigations of the thesis are as the following.First, we present a brief introduction of the magnetic frustration and ferroelectricity of the rare-earth manganites RMnO3 with distorted perovskite structures (hexagonal or orthorhombic). The research background, crystal structure and research status of these three different coupling systems are introduced.Second, a general introduction of the optical floating zone method, the principle of single crystal growth, polycrystalline preparation and experimental procedures are introduced.Third, a magnetic measurement system in the pulsed high magnetic field is designed.Fourth, the magnetic properties of the frustrated hexagonal YMnO3 and orthorhombic EuMnO3 are investigated, and the doping effect of these single crystal materials of Y1-xErxMnO3, Eu1-xYxMnO3 and Y1-xTb-xMnO3 are investigated. Results suggest that the magnetic or nonmagnetic ions doping has important effect on the magnetic properties of the mother compound of YMnO3, in which the frustration effect is the doping level dependence. Meanwhile, the Mn3+moments reorientation behavior is observed in the doping system, which indicates that doping brings complicated magnetic structure and the coexist of multi-phases.Five, the abnormal magnetization and field-induced transition in (La1-xBix)0.67Cao.33MnO3(x=0.2,0.27) are investigated. Results suggest that the coexistence of the charge order and ferromagnetic phase in the low temperature. And the irreversible phenomenon of the filed-induced ferromagnetic transition is observed. In the high temperature region, the content of ferromagnetic phase decreases and ferrimagnetic and paramagnetic phases increase.Sixth, the magnetic and structure properties of the low dimensional cobalt oxygen compounds with the perovskite-like structure are investigated. For Sr6Co5O15-δsingle crystal, the experiments results suggest that oxygen deficient have much effect on the magnetic properties. Theory calculations confirm the high field magnetization behavior measured in pulsed high magnetic field. Meanwhile, nonmagnetic Mg2+ions doping in quasi-one-dimensional BaCo2V2O8 make the long range order destroy andthe inter-chain interaction increase.