Temperature dependence of magnetoresistance in magnetic tunnel junctions with different free layer structures

Abstract

The temperature and bias voltage dependence of magnetoresistance and the resistance of two types of magnetic tunnel junction (MTJ) samples were studied. These two types of MTJ samples have different free layer structures, while having the same pinned layer structures and with the same material for free and reference layers. The layer structure for type 1 MTJs is $80\mathrm{Ru}\text{\penalty1000-\hskip0pt}8\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{\penalty1000-\hskip0pt}15{\mathrm{Al}}_{2}{\mathrm{O}}_{3}\text{\penalty1000-\hskip0pt}50\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{\penalty1000-\hskip0pt}9\mathrm{Ru}\text{\penalty1000-\hskip0pt}54\mathrm{Fe}\mathrm{Co}\text{\penalty1000-\hskip0pt}350\mathrm{Cr}\mathrm{Mn}\mathrm{Pt}$ (in angstroms). The layer structure for type 2 MTJs is $80\mathrm{Ru}\text{\penalty1000-\hskip0pt}40\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{\penalty1000-\hskip0pt}50\mathrm{Ru}\mathrm{Ta}\text{\penalty1000-\hskip0pt}40\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{\penalty1000-\hskip0pt}15{\mathrm{Al}}_{2}{\mathrm{O}}_{3}\text{\penalty1000-\hskip0pt}50\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{\penalty1000-\hskip0pt}9\mathrm{Ru}\text{\penalty1000-\hskip0pt}54\mathrm{Fe}\mathrm{Co}\text{\penalty1000-\hskip0pt}350\mathrm{Cr}\mathrm{Mn}\mathrm{Pt}$. The tunneling magnetoresistance (TMR) ratio $[({R}_{\mathit{AP}}\text{\penalty1000-\hskip0pt}{R}_{P})∕{R}_{P}]$ is about 26% and 69% at room temperature for type 1 and type 2 MTJs, respectively. A TMR as high as 107% has been observed for type 2 MTJ samples at $13\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. By analysis of the voltage and temperature dependence of the resistance and magnetoresistance in these MTJs, we discuss the effects of the magnetic behavior of the free layers, barrier qualities, and barrier interfaces. The results clearly indicate that the micromagnetization orientation at the interface between the free layer and the barrier layer is one of the important factors that determines the TMR ratio.