Charge pumping in magnetic tunnel junctions: Scattering theory

We study theoretically the charge transport pumped by magnetization dynamics through epitaxial FIF and FNIF magnetic tunnel junctions (F, ferromagnet; I, insulator; N, normal metal). We predict a small but measurable dc pumping voltage under ferromagnetic resonance conditions for collinear magnetization configurations, which may change sign as a function of barrier parameters. A much larger ac pumping voltage is expected when the magnetizations are at right angles. Quantum size effects are predicted for an FNIF structure as a function of the normal layer thickness.

Figure 1

(Color online) (a) FNIF heterostructure, in which $S_{1,2}$ indicate two different scattering regions. (b) Potential profiles for majority and minority spins in $F$ are shown by solid and dashed lines. The exchange splitting is $\Delta$ and the tunnel barrier has height $U_b$ relative to the Fermi energy $E_F$.

Figure 2

(Color online) Barrier height $\left(U_b\right)$ and width $\left(d\right)$ dependence of the pumping voltage. Left: dc. Right: Maximum amplitude of ac voltage.

Figure 3

(Color online) $V_{\mathrm{cp}}$ vs N-layer thickness $a$ for FNIF $(U_b=0.25E_F)$.