Abstract
Near the metal-insulator transition, the Hall coefficient R of metal-insulator composites (M-I composite) can be up to 104 times larger than that in the pure metal called Giant Hall effect. Applying the physical model for alloys with phase separation developed in [1] [2], we conclude that the Giant Hall effect is caused by an electron transfer away from the metallic phase to the insulating phase occupying surface states. These surface states are the reason for the granular structure typical for M-I composites. This electron transfer can be described by [1] [2], provided that long-range diffusion does not happen during film production (n is the electron density in the phase A. uA and uB are the volume fractions of the phase A (metallic phase) and phase B (insulator phase). β is a measure for the average potential difference between the phases A and B). A formula for calculation of R of composites is derived and applied to experimental data of granular Cu1-y(SiO2)y and Ni1-y(SiO2)y films.
Highlights
Nanocomposites play a growing role in both scientific research and practical applications because of the possibility of combination of special properties which cannot be reached in classical materials [3]-[5]
This model can be summarized by three points1: For large ranges of concentration there is (1) Phase separation between two phases called phase A and phase B, where each phase has its “own” short-range order (SRO), (2) The phase separation leads to band separation in the conduction band (CB) and valence band (VB) connected with the phases A and B, respectively, and the electrons are freely propagating and the corresponding wave functions are extended over connected regions of one phase as long as the phase forms an infinite cluster through the alloy
A formula is derived for the Hall coefficient R of composites and applied to a discussion of the concentration dependence of R in M-I composites
Summary
Nanocomposites play a growing role in both scientific research and practical applications because of the possibility of combination of special properties which cannot be reached in classical materials [3]-[5]. We present a discussion of the reasons for the GHE applying the electron transfer model [1] [2] developed for metal-metalloid alloys. This model can be summarized by three points: For large ranges of concentration there is (1) Phase separation between two phases called phase A and phase B, where each phase has its “own” short-range order (SRO), (2) The phase separation leads to band separation in the conduction band (CB) and valence band (VB) connected with the phases A and B, respectively, and the electrons are freely propagating and the corresponding wave functions are extended over connected regions of one phase as long as the phase forms an infinite (macroscopic) cluster through the alloy.
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