Development And Application Of Magneto-Optical Imaging System Under Pulsed Magnetic Field

The measurement technique under high magnetic field has developed rapidly in recent years. High magnetic field can induce changes in electronic state, magnetic moment and microstructure of different material which will eventually help us understand the physical theory. Nowadays, various measurement method has been found under both pulsed and static high magnetic field such as magnetization measurements, electrical transport measurements, polarization measurements, thermal capacity measurements etc.. Especially, breakthrough has been made in the magneto-optical micro imaging method, using this method the microstructure of the material surface can be observed under high magnetic field. However due to the technique difficulties few of this method has been done under pulsed high magnetic field. While the technique of high speed filming, cryogenics and pulsed high magnet moves forward, magneto-optical imaging (MOI) solution under pulsed high magnetic field becomes possible. In this paper, after the MOI system in institute for solid state physics attached to the university of Tokyo we’ve developed the first MOI system in China. Several experimental researches have been done using MOI method by this equipment. The main investigations of the thesis are as the following.First, we present a brief introduction to the measurement methods under high magnetic field. Among them, the advantage of using MOI method is to observe more detail of the material surface in micro scale. The significance of this method under pulsed high magnetic field will certainly heighten the max field and reduce both the cost of the static field equipment and the relying on liquid helium.Second, we have successfully made the first pulsed magnetic field MOI system in the country. To describe this system we introduced several aspect of it, such as power, pulsed magnets, cryogenic vacuum systems, imaging acquisition and signal measurements. Both software simulations and experimental tests have been made to magnet field and thermal conduct, furthermore we introduced the magneto-optical Kerr imaging and the signal acquisition method.Thirdly, after the test of the equipment, we performed MOI observation of CuFeO2under extreme temperature and pulsed high magnetic field which shows the magnetic domain of the CuFeO2and the changes induced by magnetic field. To indicate the magnetization of the material surface we analyzed the Kerr light intensity through the pulsed magnetic field and confirmed the possibility of measuring the magnetization using MOI method.Fourthly, we have investigate the Ni-Mn based ferromagnetic shape memory alloy (FSMA) which are rich for various transitions and physical characteristics. Using the MOI method we investigate the martensite transition of Ni-Mn based FSMA both induced by thermal and magnetic field. For the first time, using in situ observation we shows the direct evidence of the irreversibility of Ni-Mn-Sn martensite transition induced by magnetic field. Further more, we investigate the NiMnInAl alloy and confirmed the reversibility of the martensite transition induced by magnetic field.