The interface magnetism between Co2FeGe Heusler alloy layers and MgO layers was investigated using Fe-57 Mossbauer spectroscopy. Interface-sensitive samples, where the Fe-57 isotope was used only for the interfacial atomic layer of the Co2FeGe layer on the MgO layer, were prepared using atomically controlled alternate deposition. The Fe-57 Mossbauer spectra of the interface-sensitive samples at room temperature were found similar to those of the bulk-sensitive Co2FeGe films in which the Fe-57 isotope was distributed throughout the films. On the other hand, the tunnel magneto-resistance effect of magnetic tunnel junctions with Co2FeGe layers as the ferromagnetic electrodes showed strong reduction at room temperature. These results indicate that the strong temperature dependence of the tunneling magnetoresistance of magnetic tunnel junctions using Heusler alloy electrodes cannot be attributed simply to the reduction of the magnetization at the interfaces between the Heusler alloy and insulator layers. (C) 2014 AIP Publishing LLC.