Effect of pressure on magnetotransport properties in Fe/MgO granular films

Abstract

A special example of granular thin films is the discontinuous metallic and insulator multilayers (DMIMs) consisting of metallic layers with different degrees of discontinuity intercalated between insulating layers. However, the studies about the effect on the magneto-transport properties of the hydrostatic pressure are scarce. In this work we report the effect of hydrostatic pressure on the resistance and magnetoresistance of a DMIM of nominal composition [Fe(t=0.7nm)/MgO(t=3 nm)]15 ,deposited on a substrate of corning glass. The DMIM has been characterized previously showing a superparamagnetic behaviour. The resistivity has been measured at room temperatures with hydrostatic pressure (Ph) up to 7 Kbar. The resistivity decreases linearly with pressure, indicating an increase in conduction via tunneling. The value of the coefficient, (1/ρ0)dρ/dPh =-3.9 10-2 kbar-1 is higher than the value obtained in other granular films. This result implies that the electronic state of the DMIM is near the percolation threshold. Magnetoresistance (MR) isotherms have been measured at room temperatures for Ph=1bar and Ph=7Kbar. At the maximum applied magnetic field (3KOe) the MR increases from 0.6% at ambient pressure to 1.1% at 7 Kbar. This result will be explained due to the reduction of the tunnel barrier induced by the hydrostatic pressure.