Charge and Spin Processes in Anisotropic Materials

Several materials have been investigated in order to study charge and spin processes in anisotropic materials, particularly in high magnetic fields. The behavior of charge carriers in graphite based material, such as bulk graphite, mesoscopic graphite and graphite intercalated compound is studied. In novel spin systems, a dense Kondo system, CeAgSb2 which has ferro- and antiferro-magnetic ordering depending on the direction of the magnetic field has been selected, in order to study the behavior of the spin in this system. Here, I present briefly an explanation of each part of this work. The nature of the magnetic field dependent metal-insulator behavior has been investigated in bulk highly oriented pyrolytic graphite at low temperatures by electronic transport. The metal-insulator behavior has been examined by applying uniaxial stress to our sample up to 8 kbar and found that the temperature dependence of the resistivity for different magnetic fields is the same as that in ambient pressure. The temperature dependence of the resistivity in mesoscopic graphite (called as few layer graphene or FLG) has a strong dependence on the thickness of the sample. The effect of electric field in FLG has been studied in both magnetic fields and zero field. The Shubnikov-de Haas (SdH) oscillations frequency increases with absolute value of the gate voltage. I do not observe the field induced charge density wave transition, which is observed in bulk graphite. The intercalated graphite superconductor CaC6 with Tc ~ 11.5 K has been synthesized and characterized with magnetoresistance measurements. By using the McMillan formula, the electron-phonon coupling constant is estimated to be ʎ = 0.85 which places this material in the intermediate-coupling regime. The angular dependence of the upper critical field parallel and perpendicular to the superconducting planes suggests that this material is a quasi-2D superconductor. Of the dense Kondo materials in the class CeTSb2 (where T = Au, Ag, Ni, Cu, or Pd), CeAgSb2 is special due to its complex magnetic ground state, which exhibits both ferro- and anti-ferromagnetic character below an ordering temperature TO ~ 9.8 K. To further elucidate a description this magnetic ground state, I have carried out a systematic study of single crystalline CeAgSb2 by magnetic, electrical magneto-transport, and SdH studies. At zero field the temperature dependent resistivity below TO is most consistent with antiferromagnetic order, based on transport theory which includes magnon scattering.