Relationship of tunnelling magnetoresistance and buried-layer densities of states as derived from standing-wave excited photoemission

We have measured the valence-band densities of states (DOSs) in buried CoFeB and CoFe layers in a magnetic tunnel junction using a novel extension of a recently developed standing wave/wedge soft x-ray photoemission technique. The CoFe DOS at the Fermi level is substantially enhanced when the CoFe thickness is reduced from 25 to 15 Å. This enhancement, which we suggest is due to the amorphous character of the CoFe when in thickness and results in a spin-polarized peak in the DOS of primarily Co origin, can be directly correlated to marked improvements in magnetic transport and switching properties. This technique for studying buried-layer DOSs should also be applicable to other multilayer nanostructures. © 2006 IOP Publishing Ltd.