Regensburg 2007 – scientific programme
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MA: Fachverband Magnetismus
MA 12: Spindependent Transport I
MA 12.5: Talk
Tuesday, March 27, 2007, 11:15–11:30, H22
Spin Polarization at the Co / MgxO1-x interface: the influence of interface stoichiometry — •Frank Matthes1, Liu-Niu Tong2, Martina Müller1, and Claus M. Schneider1 — 1Institute of Solid State Research, Research Centre Jülich, 52425 Jülich, Germany — 2Institute of Material Science and Engineering, Anhui University of Technology, Ma-An-Shan, 243002, Anhui, China
One decisive factor for the functionality of single crystalline magnetoresistive tunnelling junctions, like Fe/MgO/Fe or Co/MgO/Co, are the spin transport properties through the interface between ferromagnet and isolator. In this study, we extended our earlier studies of Fe/MgO to the Co/MgO system, because i) the affinity to form oxides at the interface should be less compared to Fe/MgO , ii) theoretically, a higher tunnelling magnetoresistive ratio is predicted and iii) we want to compare the results of both systems. We modified the interfacial bonding conditions by precisely controlling the amount of oxygen offered during growth of MgO. Utilizing spin polarized valence band photoemission spectroscopy, we studied the electronic band structure of bct Co and monitor its modification upon the coverage with MgO layers of different stoichiometries. Upon coverage with MgO of correct stoichiometry, we determined an unexpected attenuation of the spectral weight for transitions originating from Δ5 spin down initial states. The oxygen deficiency in MgO caused a positive increase in the measured spin polarization. Analogue observations existing in the Fe/MgO system lead to the assumption that similar mechanism is responsible for the observed effects in both systems.