Possible adiabatic polaronic hopping in Ca1-xEuxB6 (x=0.005, 0.01, and 0.05)

Abstract

Using temperature- and field-dependent resistivity rho(T,H) measurements, we investigate the anomalous transport properties of a series of compounds of Ca1-xEuxB6 (x=0.005, 0.01, and 0.05). It is found that the electrical transport in Ca1-xEuxB6 (x=0.005, 0.01, and 0.05) at high temperatures (T >= 100 K) is dominated by polaron hopping in an adiabatic regime. Magnetoresistance, defined by Delta rho/rho(0)=[rho(H)-p(0)]/rho(0), is also found to be positive and follows Kohler's rule for compounds of x =:0.005 and 0.01, indicating that the transport property is also dominated by a normal metallic conduction. Comparing the results in this study with the polaron hopping model in a nonadiabatic regime for Ca1-xEuxB6 (x >= 0.1) [Jong-Soo Rhyee et al., Phys. Rev. B 67, 125102 (2003)], we suggest that the hopping mechanism changes gradually from adiabatic to nonadiabatic hopping with increasing Eu concentration.