Band-Edge Noise Spectroscopy of a Magnetic Tunnel Junction

We propose a conceptually new way to gather information on the electron bands of buried metal-(semiconductor-) insulator interfaces. The bias dependence of low frequency noise in Fe1-xVx/MgO/Fe(0 < x < 0.25) tunnel junctions shows clear anomalies at specific applied voltages, reflecting electron tunneling to the band edges of the magnetic electrodes. The change in magnitude of these noise anomalies with the magnetic state allows evaluating the degree of spin mixing between the spin polarized bands at the ferromagnet-insulator interface. Our results are in qualitative agreement with numerical calculations.