A simple formulation for magnetoresistance in metal-insulator granular films with increased current

Abstract

We studied the tunnel magnetoresistance in metal/insulator granular films when the applied current is varied. The tunnel magnetoresistance shows a strong modification related to a non-Ohmic behaviour of theses materials. It was verified that spin-dependent tunnelling is the main mechanism for magnetoresistance at low applied current. However, when the current is high, another mechanism gets to be important: it is independent of the magnetization and is associated to variable range hopping between metallic grains. In this work, we propose a simple modification of Inoue and Maekawa’s model for tunnelling magnetoresistance in granulars, rewriting the expression for resistance as a function of magnetic field and temperature, also taking into account the two different contributions.