Abstract
Magnetic tunnel junctions (MTJs) with thin crystalline MgO(001) barriers displaying large tunnel magnetoresistance (TMR) and low resistance-area product (R×A) will likely be used as the next generation sensors in read heads of ultrahigh density hard drives. However, the thin insulting barrier may result in the unwanted presence of metallic pinholes joining the two electrodes. Here we study the transport properties of thin MgO-based low resistance MTJs (barrier thickness, t=0.6nm), deposited by physical vapor deposition, with R×A values as low as 8Ωμm2 and TMR as high as 70% at room temperature. We performed temperature dependent (300–20K) resistance and magnetoresistance measurements on different samples of the same series and observed different behaviors for different samples and magnetic states. All samples showed positive dR∕dT for the parallel state due to the presence of pinholes in the barrier. However, in the antiparallel state the R(T) curves always exhibit a mixed character, with dR∕dT changing from negative to positive with decreasing temperature. Our results then show an interesting competition between tunnel and metallic transport in the studied samples.
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