A first principle study of the massive TMR in magnetic tunnel junction using Fe 3 Al Heusler alloy electrodes and MgO barrier Worasak Rotjanapittayakul 1, a , Thomas Archer 2, b , Stefano Sanvito 3, c and Wanchai Pijitrojana 4, d 1, 4 Department of Electrical and Computer Engineering, Faculty of Engineering, Thammasat University, Bangkok, 10120, Thailand 2, 3 School of Physics and CRANN, Trinity College Dublin, Ireland a r.borwornsak@gmail.com, b archert@tcd.ie, c sanvitos@tcd.ie, d pwanchai@engr.tu.ac.th Keywords: Tunneling Magnetoresistance, Magnetic Tunnel Junction, Heusler alloy Abstract. The massive tunnel magnetoresistane (TMR) is expected when Fe 3 Al Heusler alloy are used for magnetic electrodes in magnetic tunnel junction (MTJ). We demonstrate the Fe 3 Al/MgO/Fe 3 Al MTJ, which have good lattice matching interfaces. The electronic and transport properties of these system are systematically investigated by first principle calculation. The electronic band structure of Fe 3 Al Heusler alloy and MgO are represented for discussion spin filtering effect. Besides, the transmission conductance is calculated to study the spin tunneling effect. We found that the massive TMR is clearly achieved at zero-bias condition, and the TMR is decreased when the finite bias are applied. Thus, among ferromagnetic materials, the Fe 3 Al Heusler alloy will be good alternative to bcc-Fe based electrodes with MgO barrier for the MTJs beyond. Introduction The magnetic tunnel junction (MTJ) component consists of two ferromagnetic (FM) electrodes sandwiching a tiny insulating barrier. The tunneling magnetoresistance (TMR) ratio is the primary property of a MTJ, the electrical resistance/spin injection can depend either on magnetization of electrodes, which were controlled by an applied external magnetic field or spin-polarized current [1, 2]. Generally, to achieve a high spin injection the ordinary approach is using an insulator to select the spin carriers from the ferromagnet. The Fe/MgO/Fe MTJ was proposed to achieve a large TMR (1,000%) using bcc-Fe as ferromagnetic electrodes and fcc-MgO as insulating barrier [3]. For the further approaches, some half-metallic ferromagnets (HMFs) Heusler alloys have been investigated for the magnetic electrodes, because their exist a gap in one spin state, correspond to high spin polarization (100%) at Fermi energy and then enhance the efficiency carriers of spin injection which initiated to achieve high TMR. In addition, the interfacial strain and roughness in multilayer are also essential to the spin injection and TMR, hence in oder to achieved a large TMR the scientists investigate materials in the multilayer of MTJs with the similar lattice constant to reduce an interfacial strain [4]. Among the plenty of HMFs, some Heusler alloys electrodes were fabricated in MTJs due to their large magnetic moment per cell such as Co 2 FeSi, Co 2 MnSi and Co 2 FeAl [5-7]. The high spin polarization of HMFs Heusler alloys is losing because the ordered-disorder transition and defects, although HMFs Heusler alloys have high spin polarization. The Fe 3 Al intermetallic alloy in Heusler phase has attracted a great interest for high temperature application due to a large magnetic moment 5.61 μB/cell and high Curies temperature (780K) were found in ordered Fe 3 Al (D0 3 ) [8,14]. Generally, a single crystalline MgO is widely used as an insulating barrier of MTJs because a wide band gap and good selection carriers of spin injection were clarify [9]. Besides, the Fe 3 Al (110) layer have a small lattice mismatched with MgO (001) layer due to experimental lattice constant of bulk Fe 3 Al Heusler alloy and MgO are 5.792 and 4.212 Å, respectively. In this paper we report a first principle study of the Fe 3 Al/MgO/Fe 3 Al system due to electronic and transport properties. The