Tunneling magnetoresistance anomalies in a Coulomb blockaded quantum dot

We consider quantum transport and tunneling magnetoresistance (TMR) through an interacting quantum dot in the Coulomb blockade regime, attached to ferromagnetic leads. We show that there exist two kinds of anomalies of TMR, which have different origins. One type, associated with the TMR sign change and appearing at conductance resonances, is of a single-particle origin. The second type, inducing a pronounced increase in TMR value far beyond 100%, is caused by electron correlations. It is manifested in between Coulomb blockade conductance peaks. Both types of anomalies are discussed for zero and finite biases, and their robustness to the temperature increase is also demonstrated. The results are presented in the context of recent experiments on semiconductor quantum dots in which similar features of TMR have been observed.