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

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 $80\mathrm{Ru}\text{‐}8\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{‐}15{\mathrm{Al}}_2{\mathrm{O}}_3\text{‐}50\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{‐}9\mathrm{Ru}\text{‐}54\mathrm{Fe}\mathrm{Co}\text{‐}350\mathrm{Cr}\mathrm{Mn}\mathrm{Pt}$ (in angstroms). The layer structure for type 2 MTJs is $80\mathrm{Ru}\text{‐}40\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{‐}50\mathrm{Ru}\mathrm{Ta}\text{‐}40\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{‐}15{\mathrm{Al}}_2{\mathrm{O}}_3\text{‐}50\mathrm{Co}\mathrm{Fe}\mathrm{B}\text{‐}9\mathrm{Ru}\text{‐}54\mathrm{Fe}\mathrm{Co}\text{‐}350\mathrm{Cr}\mathrm{Mn}\mathrm{Pt}$. The tunneling magnetoresistance (TMR) ratio $[\left(R_{\mathit{AP}}\text{‐}{R}_P\right)∕R_P]$ 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 $13\mathrm{K}$. 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.

Figure 1

(Color online) The layer structures of (a) type 1 and (b) type 2 MTJ samples.

Figure 2

(Color online) Magnetoresistance transverse loops for (a) type 1 and (b) type 2 MTJs between temperature 13 and $300\mathrm{K}$.

Figure 3

(Color online) The squareness $\left(S\right)$ and hysteresis field $\left(H_c\right)$ of type 1 and type 2 MTJs.

Figure 4

(Color online) Conductance vs bias voltage at $13\mathrm{K}$ for type 1 in the (a) $P$ state and (b) $\mathit{AP}$ state and for type 2 in the (c) $P$ state and (d) $\mathit{AP}$ state.

Figure 5

(Color online) Temperature dependence of the resistance area product (RAP) in the $P$ and $\mathit{AP}$ states for (a) type 1 and (b) type 2 MTJs.

Figure 6

(Color online) Temperature dependence of TMR for (a) type 1 and (b) type 2 MTJs.

Figure 7

(Color online) Voltage dependence of TMR at different temperatures for (a) type 1 and (b) type 2 samples and voltage dependence of ${\mathrm{V}}_{\mathrm{out}}$ (defined as $V^{*}\mathrm{TMR}$) for (c) type 1 and (d) type 2 samples. The direction of bias voltage is defined with respect to upper electrode.