Negative and linear positive magnetoresistance effect in silver-rich silver selenide

In the non-magnetic semiconduct or silver selenide (Ag2+delta Se) with a minor heterogeneous silver excess (0.79 x 10(-4) < delta <= 1 X 10(-2)) we measured either a saturating negative magnetoresistance. (MR) effect, a linear positive MR effect or a, superposition of both. This complex MR behavior depends on the amount of the silver metal excess, but-is also strongly influenced by the thermal treatment of the samples. Excess silver that cannot be at accommodated homogenously in the silver selenide lattice creates structural heterogeneities and forms a microstructure which is controlled by the thermal annealing procedure. We suggest that small silver segregations at the grain boundaries of the silver selenide matrix ("nanofilms") are responsible for the negative MR effect, whereas nanoscale silver particles within the silver selenide matrix (nanoparticles) cause a linear positive effect. (c) 2008 Elsevier Mason SAS. All rights reserved.