The physics of nanostructures have extended the frontier of quantum mechanics and have realized several important quantum effects, such as the Kondo effect in quantum dot (QD), the Aharonov-Bohm (AB) effect, etc. Recent fabrication technique of magnetic nanostructures evolved the active research field \'spintronics\'. The nanospintronics devices possess basic interest since they provide a way to control the spin degrees of freedom and realize novel many-body states. We analyze the possibility of the Kondo effect in a QD coupled for two ferromagnetic leads. We show that for parallel alignment of magnetizations, the zero-bias anomaly is split. For antiparallel alignment and symmetric coupling, the Kondo resonance recovers and splitting is suppressed. We show that such anomalous behavior induces a negative large dip in bias voltage dependence of the tunnel magnetoresistance. We also theoretically investigate the Ruderman-Kittel-Kasuya-Yosida (RRKY) interaction between two semiconducting QDs embedded in an AB ring. In such a system, the RKKY interaction can be controlled by the flux and the flux-dependent RKKY interaction dominates the conductance. For the ferromagnetic coupling, the amplitude of AB oscillations is enhanced by the Kondo correlations. For the antiferromagnetic coupling, the phase of AB oscillations is shifted by pi. Discussed many-body effects, which were very recently demonstrated experimentally, can be utilized for future nanospintronics devices.