Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We provide compelling evidence to establish that, contrary to one's elementary guess, the tunneling spin polarization (TSP) of amorphous CoFeB is larger than that of fcc CoFeB. First-principles atomic and electronic structure calculations reveal striking agreement between the measured TSP and the predicted s-electron spin polarization. Given the disordered structure of the ternary alloy, not only do these results strongly endorse our communal understanding of tunneling through AlO x , but they also portray the key concepts that demand primary consideration in such complex systems.

We report a correlation between the spin polarization of the tunneling electrons and the magnetic moment of amorphous CoFeB alloys. Such a correlation is surprising since the spin polarization of the tunneling electrons involves s-like electrons close to the Fermi level (E_{F}), while the magnetic moment mainly arises due to all the d electrons below E_{F}. We show that probing the s and d bands individually provides clear and crucial evidence for such a correlation to exist through s-d hybridization, and demonstrate the tunability of the electronic and magnetic properties of CoFeB alloys.

We present measurements of tunneling spin polarization of Co 72 Fe 20 B 8 in Al/ AlO x / CoFeB tunnel junctions using superconducting tunneling spectroscopy. We consistently observe high spin polarization ͑above 53%͒, higher than that measured for comparable CoFe alloys, indicating a crucial role played by the 8% atomic boron. X-ray diffraction measurements on 700 Å thick films reveal an amorphous structure for as-deposited films, while anneals above 250°C initiate a gradual crystallization. Superconducting quantum interference device magnetometery shows that the magnetic moment exhibits minor changes after anneals, but there is a dramatic change in the coercivity after anneals above 400°C. However, these structural and magnetic changes induce only a slight change in the tunneling spin polarization of CoFeB.

We examine the role of Mn diffusion in the thermal stability of tunneling spin polarization P by directly measuring P of Al∕AlOx∕Co∕FeMn and Al∕AlOx∕Co90Fe10∕FeMn junctions using superconducting tunneling spectroscopy (STS). We confirm Mn diffusion in our junctions using x-ray photoelectron spectroscopy after an ultrahigh vacuum 500°C anneal. Surprisingly, and in contrast to the current belief, no drop in P is observed using STS. Therefore, though Mn diffuses significantly, it cannot be solely responsible for the drop in tunneling magnetoresistance observed after postdeposition anneals above 300°C.

We present measurements of tunnelling spin polarization (TSP) of CoFeB alloys in Al/AlOx/CoFeB tunnel junctions using superconducting tunnelling spectroscopy. We observe that though Co72Fe20B8 (at.%) layers crystallize in the fcc structure, in junctions annealed above 300 °C the measured TSP degrades, indicating that in these junctions the TSP of amorphous CoFeB is higher than its crystalline counterpart.