Fabrication of Magnetic Tunnel Junctions With Co$_{2}$ FeSi Heusler Alloy and MgO Crystalline Barrier

Abstract

Tunneling magnetoresistance (TMR) characteristics of magnetic tunnel junctions with a Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeSi electrode and an MgO crystalline barrier have been investigated. Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeSi Heusler alloy electrode grown on Cr-buffered MgO(100) substrate starts to have an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> 2 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> structure when annealed above 420degC. In the cases of CoFeB/MgO/Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeSi junctions, a high TMR ratio of 158% has been achieved after annealing at 350degC, which is obtained by coherent tunneling between the electrodes and barrier, not by the half-metallic nature of Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeSi Heusler alloy. However, the Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeSi Heusler alloy electrode degrades the TMR ratio when compared with an amorphous CoFeB electrode and the bottom Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeSi electrode makes more degradation of the TMR ratio than the top Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeSi electrode. The major reason for the low TMR ratio in Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeSi-based junctions is the broken epitaxial relationship between the bottom Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeSi electrodes and the MgO crystalline barrier, which is investigated by a cross-sectional transmission electron micrograph.