LAUSR

The paramagnetic defects in the magnesium-oxide (MgO) thin-film grown on a silicon (Si) substrate (MgO|Si) by a molecular beam epitaxy method are reported. These thin films have been used as an MgO tunnel barrier material for the spin-injection to Si from Fe. According to the crystallinity evaluation, the MgO film possessed a (001) oriented structure. We investigated the paramagnetic defects and impurities of several MgO|Si samples by electron paramagnetic resonance (EPR). The EPR spectra showed a strong isotropic signal with a g-value of 2.002 and six weak satellite peaks which were assigned to oxygen vacancies of highly oriented MgO(001) (F+ center) coupled with 25Mg nuclei (I = 5/2). The spin area density of MgO (thickness = 1.6 nm), which can be used as a tunnel barrier for spin injection, was determined to be 7 × 1013 cm−2. This value corresponds to 1% of O atoms replaced with vacancies. The identification of the paramagnetic centers and the quantitative estimation of their concentration in MgO films...