Dynamic Spin-Polarized Resonant Tunneling in Magnetic Tunnel Junctions

Precisely engineered tunnel junctions exhibit a long sought effect that occurs when the energy of the electron is comparable to the potential energy of the tunneling barrier. The resistance of metal-insulator-metal tunnel junctions oscillates with an applied voltage when electrons that tunnel directly into the barrier’s conduction band interfere upon reflection at the classical turning points: the insulator-metal interface and the dynamic point where the incident electron energy equals the potential barrier inside the insulator. A model of tunneling between free electron bands using the exact solution of the Schrödinger equation for a trapezoidal tunnel barrier qualitatively agrees with experiment.

Figure 1

Differential resistance measurements of NiFe devices at 5 K in the $p$ and $ap$ magnetic configurations. (inset) The bias dependence of $d{I}_p/dV$ for NiFe (green squares) is fit well by a 4th order polynomial (black line).

Figure 2

Normalized differential magnetoresistance for NiFe (bottom, blue), CFB1 (middle, red), and CFB2 (top, black) at 300 K. The nominal dMR ($V=0$) and resistance-area products were 80% and $3.1\mathrm{k}\Omega ·\mu {\mathrm{m}}^2$ for NiFe, and 120% and $6.0\mathrm{k}\Omega ·\mu {\mathrm{m}}^2$ for both CFB devices. The barrier heights (eV) from BDR fits of $d{I}_p/dV$ are indicated schematically to the right, and a cartoon of electron standing waves is shown to the left.

Figure 3

Model results for the dMR bias dependence for NiFe (blue line), CFB1 (red dots), and CFB2 (black dashes) show qualitative agreement with experiment. For a thickness of 28 Å and no roughness, the barrier heights (eV) used in the model are indicated schematically to the right.