Europhys. Lett, 45 (3), pp. 368-373 (1999)
The level-shifting-induced negative magnetoresistance
in the nearest-neighbor hopping conduction
X. R. Wang 1, S. C. Ma 1 and X. C. Xie 2
1 Department of Physics, The Hong Kong University of Science
Clear Water Bay, Hong Kong
2 Department of Physics, Oklahoma State University - Stillwater, OK 74078, USA
(received 21 July 1998; accepted in final form 26 November 1998)
PACS. 72.80Tm - Composite materials.
PACS. 75.70Pa - Giant magnetoresistance.
PACS. 81.05Rm - Porous materials; granular materials.
We propose a new mechanism of negative magnetoresistance in non-magnetic granular materials in which electron transport is dominated by hopping between two nearest-neighbor clusters. We study the dependence of magnetoresistance on temperature and separation between neighboring clusters. At a small separation we find a negative magnetoresistance at low temperatures and it changes over to a positive value as temperature increases. For a fixed temperature, magnetoresistance changes from negative to positive when the cluster separation increases. The change of magnetoresistance can be more than 80 % at low temperatures.