Giant Coulomb blockade magnetoresistance in magnetic tunnel junctions with a granular layer

We show that the Coulomb blockade voltage can be made to depend strongly on the electron spin in a discontinuous magnetic granular layer inserted in the middle of an insulating layer of a tunnel junction. This strong spin dependence is predicted from the local intergranular magnetoresistance effects, including giant magnetoresistance (GMR), tunneling magnetoresistance, colossal magnetoresistance, or GMR through a polymer spacer. The resulting Coulomb blockade magnetoresistance (CBMR) ratio can exceed the magnetoresistance ratio of the granular layer itself by orders of magnitude. Unlike other magnetoresistance effects, the CBMR effect does not require magnetic electrodes.

Figure 1

(a) When the moments of two magnetic QDs are antiferromangetically oriented, the CB voltage is $V_c$ for each dot. (b) An external magnetic field aligns the moments of the two dots, which are now coupled electronically due to enhanced interdot tunneling, and the CB voltage is reduced to $V_c/2$.

Figure 2

(Color online) (a) Ratio $G_H\left(V\right)/G_0\left(V\right)$ given by Eq. (13) for two spin-dependent QD size distributions, ${\lambda }_H/{\lambda }_0=1.1$, and ${\lambda }_H/{\lambda }_0=2$. (b) Comparison of Eq. (13) with experiment (Ref. 18) for a LaSrMnO/SrTiO/LaSrMnO junction with the fitted parameters ${\lambda }_H/{\lambda }_0=2.33$ for $H=4\text{T}$ and ${\lambda }_H/{\lambda }_0=4.67$ for $H=14\text{T}$.