Effect of Interface Roughness on Magnetoresistance and Magnetization Switching in Double-Barrier Magnetic Tunnel Junction

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The three kinds of double-barrier magnetic tunnel junction (DMTJ) with or without amorphous ferromagnetic Co<formula formulatype="inline"><tex Notation="TeX">$_{70.5}$</tex> </formula>Fe<formula formulatype="inline"><tex Notation="TeX">$_{4.5}$</tex> </formula>Si<formula formulatype="inline"><tex Notation="TeX">$_{15}$</tex> </formula>B<formula formulatype="inline"><tex Notation="TeX">$_{10}$</tex> </formula> (in at. %) free-layer were investigated to understand the effect of the free-layer on the bias voltage dependence of tunneling magnetoresistance (TMR) ratio. The DMTJ structure consisted of Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO<formula formulatype="inline"><tex Notation="TeX">$_{\rm x}$</tex></formula>/free-layer 7/AlO<formula formulatype="inline"><tex Notation="TeX">$_{\rm x}$</tex></formula>/CoFe 7/IrMn 10/Ru 60 (thickness in nm). Various free layers, such as CoFe 7, CoFeSiB 7, and CoFe 1.5/CoFeSiB 4/CoFe 1.5 were prepared and compared. The roughness values of the interface between free-layer and tunnel barrier were confirmed by using the techniques of X-ray reflectivity and transmission electron microscopy. As a result, the amorphous free-layer made the interface roughness of DMTJ smoother, reducing the interlayer coupling field and suppressing the bias voltage dependence of TMR ratio at a given voltage. </para>