Study On Single Crystal Growth Of Colossal Magnetoresistance La_2-2xSr_1+2xMn₂O₇ By Floating Zone Method And Characteristic

In 1993, the magnetoresistance effect in the manganese oxides was found larger than the conventional'giant magnetoresistance', known as the 'colossal magnetoresistance (CMR). Although CMR has been extensively studied for nearly two decades, there still remain some questions or phenomenons to be clarified. This work focus on the La2-2XSr1+2xn2O7 single crystal system because the LSMO system not only has the typical features of colossal magnetoresistance effect and a wide range of hole doping, but also has the advantages of using angle resolved photoelectrons spectroscopy (ARPES) to reveal its electronic structure.Perfect single crystals are highly demanded for investigating the important physical phenomenon because of the anisotropic properties showing in the structure of LMSO(327). By using four mirror infrared heating traveling solvent floating zone (TSFZ) method, we have successfully prepared a series of high quality LSMO single crystals. The Sr doping cotentx= 0.33,0.36,0.38,0.40,0.42. The typical size of as grown ingots isφ6×L85mm. The density and homogeneity of the ceramic feed rods is crucial for stable growth. High quality feed rods were finally obtained under our optimized conditions of processing including prefiring and sintering. And we also optimized crystal growth process parameters to obtain high quality single crystal. The TSFZ method is widely accepted as the most successful approach to growing such congruent and uncongruent melting compounds. TSFZ method is also unique as a crucible free technique and produce large temperature gradient, grow large size single crystals.X-ray diffraction (XRD) and Laue back-scattering analysis show that the single crystal samples have a perfect single phase and crystallinity. The inductively coupled plasma atomic emission spectrometry and EDX measurement show that the concentration of Sr doping is very close to the expected value. And also almost no defects were observed in crystal surface by SEM. Superconducting quantum interference device (SQUID) analysis on the different doping concentration of single crystal shows that the magnetic transition temperature reaches the maximum of 134K when x=0.36. From PPMS study on the specific heat of single crystal, we investigated the variation of electron, phonon and magnetic specific heat with doping concentration for the first time. By using the laser ARPES, we clearly observed the electron type Fermi surface and band structure which originated from dz2 orbital and centered at Gamma point for the first time. We can clearly observe the "kink" structure caused by electronic phonon interaction. And also by using the Synchrotron Radiation ARPES the band structure and the evidence of quasi-particle peak can be clearly observed.