We investigate charge transport in two-dimensional ferromagnet/feromagnet junction on a topological insulator. The conductance across the interface depends sensitively on the directions of the magnetizations of the two ferromagnets, showing anomalous behaviors compared with the conventional spin-valve. It is found that the conductance depends strongly on the in-plane direction of the magnetization. Moreover, in sharp contrast to the conventional magnetoresistance effect, in the p-n junction, the conductance at the parallel configuration is much smaller than that at the antiparallel configuration. This stems from the way how the wavefunctions connect between both sides.

4 pages, 5 figures, two potential parameters added in v2