Resonant Enhancement of Tunneling Magnetoresistance in Double-Barrier Magnetic Heterostructures

We show that spin-dependent resonant tunneling can dramatically enhance tunneling magnetoresistance. We consider double-barrier structures comprising a semiconductor quantum well between two insulating barriers and two ferromagnetic electrodes. By tuning the width of the quantum well, the lowest resonant level can be moved into the energy interval where the density of states for minority spins is zero. This leads to a great enhancement of the magnetoresistance, which exhibits a strong maximum as a function of the quantum well width. We demonstrate that magnetoresistance exceeding 800% is achievable in $\mathrm{G}\mathrm{a}\mathrm{M}\mathrm{n}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{M}\mathrm{n}\mathrm{A}\mathrm{s}$ double-barrier structures.

Figure 1

Schematic flat-band diagrams illustrating the resonant spin-valve effect

Figure 2

TMR of the one-band spin-RTD as a function of the quantum-well width. Inset: Fermi surfaces in the emitter (solid lines) and quantum well (dashed line) corresponding to the maximum TMR.

Figure 3

TMR of $\mathrm{G}\mathrm{a}\mathrm{M}\mathrm{n}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$-based spin-RTDs as a function of the quantum-well width. Upper inset: Fermi surfaces in the emitter (solid) line and quantum well (diamonds) corresponding to the maximum TMR. Lower inset: schematic band diagram.