Current Fluctuations in Ferromagnetic Tunnel Junctions

Current shot noise in a double junction consisting of a small metallic grain connected to two ferromagnetic electrodes is analysed in the limit of sequential tunneling. We show that, apart from charge fluctuations, there are strong spin fluctuations. We also show that two distinct relaxation processes can be distinguished in the frequency dependent current noise: one in a low frequency range and corresponding to spin fluctuations and another one in a high frequency range corresponding to charge fluctuations.