Low-frequency and shot noises in CoFeB/MgO/CoFeB magnetic tunneling junctions

摘要

The low-frequency and shot noises in spin-valve CoFeB/MgO/CoFeB magnetictunneling junctions were studied at low temperature. The measured 1/f noisearound the magnetic hysteresis loops of the free layer indicates that the mainorigin of the 1/f noise is the magnetic fluctuation, which is discussed interms of a fluctuation-dissipation relation. Random telegraph noise (RTN) isobserved to be symmetrically enhanced in the hysteresis loop with regard to thetwo magnetic configurations. We found that this enhancement is caused by thefluctuation between two magnetic states in the free layer. Although the 1/fnoise is almost independent of the magnetic configuration, the RTN is enhancedin the antiparallel configuration. These findings indicate the presence ofspin-dependent activation of RTN. Shot noise reveals the spin-dependentcoherent tunneling process via a crystalline MgO barrier.