The s-d exchange model as the underlying mechanism of magnetoresistance in ZnO doped with alkali metals

Abstract

High field magnetoresistance has been studied in epitaxial n-type ZnO:Na and ZnO:Li thin films in a temperature range between 4 K and 150 K. The resulting negative magnetoresistance can be well fitted using a semiempirical model of Khosla and Fischer based on third order contributions to the s-d exchange Hamiltonian. The parameters obtained from this model were carefully analyzed. One of these parameters is related to a ratio between electron mobilities at zero field (a non-exchange scattering mobility µ 0 and an exchange or spin dependent one µ J ). From Hall effect measurements µ 0 was obtained, displaying a weak temperature dependence in accordance with highly n-doped ZnO while the extracted µ J exhibits an anomalous T -dependence. On the other hand, our magnetoresistance data cannot be properly fitted using Kawabata's expression based on a weak-localization model.

Ambient aging effects on the effective energy gap of ZnO thin films

“…being the CB effective density of states (N c ¼ 2:94 Â 10 18 cm À3 for ZnO), n the carrier density obtained from Hall effect measurements in the film, 30,31 and E C the minimum of the CB. In the case of TA-Vac, n Vac ¼ 2:57 Â 10 17 cm À3 , while for TA-O 2 , n O2 ¼ 8:46 Â 10 16 cm À3 .…”

Ab-initio study of half-metallic ferromagnetism and transport characteristics of MgV2S/Se4 spinels for spintronics and thermoelectric applications

“…The double exchange (DE) theory is explored as a foundation for describing the physics of gigantic magnetoresistance manganite. The effective Hamiltonian of the DE theory is obtained from the sd-exchange model for a finite scenario of an exchange mechanism that is large than the bandgap [32]. The dynamical mean-field approach, which has been effective for several other heavily interconnected networks, is more suited for representing the system of concern due to its complexity.…”