X-ray absorption spectroscopy and magnetic circular dichroism studies of L1_0-Mn-Ga thin films

Abstract

Tetragonally distorted \(\rm{Mn}_{3-x}\rm{Ga}_x\) thin films with \(0.1< x < 2\) show a strong perpendicular magnetic anisotropy and low magnetization and thus have the potential to serve as electrodes in spin transfer torque magnetic random access memory. Because a direct capping of these films with MgO is problematic due to oxide formation, we examined the influence of a CoFeB interlayer, and of two different deposition methods for the MgO barrier on the formation of interfacial MnO for \(\rm{Mn}_{62}\rm{Ga}_{38}\) by element specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). A highly textured L1\(_0\) crystal structure of the Mn-Ga films was verified by X-ray diffraction (XRD) measurements. For samples with e-beam evaporated MgO barrier no evidence for MnO was found, whereas in samples with magnetron sputtered MgO MnO was detected, even for the thickest interlayer thickness. Both XAS and XMCD measurements showed an increasing interfacial MnO amount with decreasing CoFeB interlayer thickness. Additional element specific full hysteresis loops determined an out-of-plane magnetization axis for the Mn and Co, respectively.