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Transverse magnetoresistance (TMR) measurements have been carried out at 4.2 and 1.7 K for magnetic fields up to 25 kG. The sample used is Sb-doped Ge with an intermediate level of concentration, ~6 × 1016 cm−1. At this doping level, two conduction regimes compete in the temperature range below 4.2 K. The temperature at which one regime gives way to another is 2.6 K. The TMR at 1.7 K has been found to be greater than that at 4.2 K. Moreover, at both temperatures, TMR is larger than that predicted by TMR theory for conduction-band electrons. In our case, TMR is mainly caused by carrier reduction with partial compensation by mobility increase. It has also been found that a magnetic field of 5.6 kG has no effect on the activation energies that exist at temperatures higher than 2.6 K, while it increases the lower temperature ones.

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ABSTRACT:Recently, considerable interest has been paid to polychelates of polymeric ligand with transition metal ions in order to improve their electrical properties. Some polymeric ligand complexes of Cu(II), Ni(II), and Co(II) have been synthesized, followed by chemical and physical characterization to emphasize their structure and evaluate their electrical behavior. Direct current (dc) and alternating current (ac) electrical conductivities were measured at variable temperatures (300 -50 K). Relative dielectric permittivity ⑀Ј, dielectric loss factor ⑀Љ, and loss tangent tan ␦ were measured and discussed in relation to the presence of transition metal ions.