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(a) Schematic GaMnAs-based MTJ structure with an AlMnAs barrier studied here. (b) RA product as a function of the barrier thickness in the GaMnAs-based MTJs when the tunnel barrier is AlAs, ( and 12%), and GaAs. These data were obtained at zero magnetic field in parallel magnetization with a bias voltage of 1 mV at 3.5 K. The solid rectangles and solid triangles are the data of MTJs with an barrier with and 12%, respectively. The broken line and the open circles correspond to the data of the GaMnAs-based MTJs with AlAs (Ref. 1) and GaAs tunnel barriers, respectively. (c) Schematic valence-band diagram of the GaMnAs-based MTJ with an AlMnAs barrier. Here, the GaAs spacer layers are omitted for simplicity.
(a) Inset shows the magnetic-field dependence of RA of the MTJ with a 4-nm-thick barrier at 2.6 K with a magnetic field applied in plane along the  axis when the bias voltage is 1 mV. The main graph shows the temperature dependence of TMR of this device with a magnetic field applied in plane along the  axis when the bias voltage is 10 mV. (b) Bias dependence of TMR of the GaMnAs-based MTJs with the thickness of 3 nm (red), 4.5 nm (green), and 5 nm (blue) when the magnetic field is applied in plane along the  axis. The inset shows the magnified view near zero bias.
(a) barrier thickness dependence of the TMR, where the bias voltage was set so that the TMR became maximum in each device due to the peculiar bias dependence as shown in Fig. 2(b). The rhombic and triangle points correspond to and 12%, respectively. The measurement temperature was 3.5 K, except for the data of 175% at and measured at 2.6 K. (b) Simplified band diagram of the MTJ structure used for our calculation of the decay constant . (c) Calculated as a function of at 80 meV higher than the valence-band top of GaAs (thin curve) and at 110 meV higher than that of AlMnAs (thick curve), respectively. Here, the effective mass in GaAs and AlMnAs was assumed to be and , respectively.
Details of the structures and growth conditions of the studied MTJs comprising on substrates. “Bottom” and “Top” mean the bottom and top GaMnAs layers, respectively.
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