Large magnetoresistance at high bias voltage in double magnetic tunnel junctions

This paper reports on the magnetic and transport properties of [IrMn/CoFe]/AlOx/SL/AlOx/[CoFe/IrMn] double magnetic tunnel junctions (DMTJ) deposited by magnetron sputtering and patterned using optical lithography. The aim is to obtain a high-quality magnetoresistive hard-soft system presenting a large magnetoresistance at a high applied bias voltage. For this purpose, two DMTJ were studied where the soft layer (SL) was CoFe₁/NiFe₅/CoFe₁ (nm) and NiFe₇ (nm). The similar quality of both AlOx barriers within each sample is supported by the symmetric character of the tunnel magnetoresistance (TMR) versus the bias voltage variation. The junctions having a CoFe/NiFe/CoFe (NiFe) SL show a resistance-area product (RAP) about 35 (19) k Ω·μm², a high TMR at room temperature of 49 (20)%, and a high bias voltage at which the TMR signal is decreased to half of its maximum value, V₁2/=1.33(1.0) V. Both hard magnetic layers are rigid in negative field up to 51.5 kA/m, while the coercive field of the SL is around 1.16 and 0.48 kA/m for the DMTJ integrating, respectively, the CoFe/NiFe/CoFe and NiFe SL. The large difference of coercive fields associated with the low dependence of the TMR versus bias voltage, recommend this systems for spin electronic devices.