Citation: HEWETT Extraordinary magnetoresistance ͑EMR͒ arises in hybrid systems consisting of semiconducting material with an embedded metallic inclusion. We have investigated such systems with the use of finite-element modeling, with our results showing good agreement to existing experimental data. We show that this effect can be dramatically enhanced by over four orders of magnitude as a result of altering the geometry of the conducting region. The significance of this result lies in its potential application to EMR magnetic field sensors utilizing more familiar semiconducting materials with nonoptimum material parameters, such as silicon. Our model has been extended further with a geometry based on the microstructure of the silver chalcogenides, consisting of a randomly sized and positioned metallic network with interspersed droplets. This model has shown a large and quasilinear magnetoresistance analogous to experimental findings.

Abstract:Simulations utilising the finite element method (FEM) have been produced in order to investigate aspects of circular extraordinary magnetoresistance (EMR) devices. The effect of three specific features on the resultant magnetoresistance were investigated: the ratio of the metallic to semiconducting conductivities (σ M /σ S ); the semiconductor mobility; and the introduction of an intermediate region at the semiconductormetal interface in order to simulate a contact resistance. In order to obtain a large EMR effect the conductivity ratio (σ M /σ S ) is required to be larger than two orders of magnitude; below this critical value the resultant magnetoresistance effect is dramatically reduced. Large mobility semiconductors exhibit larger EMR values for a given field (below saturation) and reduce the magnetic field required to produce saturation of the magnetoresistance. This is due to a larger Hall angle produced at a given magnetic field and is consistent with the mechanism of the EMR effect. Since practical magnetic field sensors are required to operate at low magnetic fields, high mobility semiconductors are required in the production of more sensitive EMR sensors. The formation of a Schottky barrier at the semiconductor-metal interface has been modelled with the introduction of a contact resistance at the semiconductor-metal interface. Increasing values of contact resistance are found to reduce the EMR effect with it disappearing altogether for large values. This has been shown explicitly by looking at the current flow in the system and is consistent with the mechanism of the EMR effect. The interface resistance was used to fit the simulated model to existing experimental data. The best fit occurred with an interface with resistivity of 1.55×10 −4 Ωm (overestimate). The EMR effect holds great potential with regard to its future application to magnetic field sensors. The design of any such devices should incorporate high mobility materials (such as graphene) along with the specific features presented in this paper in order to produce effective magnetic field sensors. 72.20.My, 72.15.Gd PACS (2008):

We show that extraordinary magnetoresistance (EMR) arises in systems consisting of two components; a semiconducting ring with a metallic inclusion embedded. The important aspect of this discovery is that the system must have a quasi-two-dimensional character. Using the same materials and geometries for the samples as in experiments by Solin et al. 1,2 , we show that such systems indeed exhibit a huge magnetoresistance. The magnetoresistance arises due to the switching of electrical current paths passing through the metallic inclusion. Diagrams illustrating the flow of the current density within the samples are utilised in discussion of the mechanism responsible for the magnetoresistance effect. Extensions are then suggested which may be applicable to the silver chalcogenides. Our theory offers an excellent description and explanation of experiments where a huge magnetoresistance has been discovered 2,3 .

No abstract