J Supercond Nov Magn DOI 10.1007/s10948-016-3630-z ORIGINAL PAPER Understanding the Spin Transport in H 2 O-Adsorbed Graphene-Based Magnetic Tunnel Junction Alok Kumar Singh 1 · Sudhanshu Choudhary 1 Received: 7 July 2016 / Accepted: 12 July 2016 © Springer Science+Business Media New York 2016 Abstract First-principles calculations of spin-dependent electronic transport properties of a magnetic tunnel junction consisting of a H 2 O (water)-adsorbed graphene nanosheet sandwiched between two CrO 2 half-metallic ferromagnetic (HMF) electrodes is reported. H 2 O adsorption on graphene opens a bandgap in the graphene nanosheet which makes it more suitable for use as a tunnel barrier in magnetic tunnel junctions. It was found that H 2 O adsorption sup- presses transmission probabilities for a spin-down channel in the case of parallel configuration (PC) and also sup- presses transmission in antiparallel configuration (APC) for both spin-up and spin-down channels which result in higher tunnel magnetoresistance (TMR) at higher bias voltages in these structures. HMF electrodes were found suitable to achieve the perfect spin filtration effect and high TMR. I -V characteristics for both parallel and antiparallel magnetiza- tion states of junction are calculated. A high value of TMR ∼100 % is obtained at all bias voltages in the range of 0 to 1.2 V. High TMR suggests its usefulness in spin valves and other spintronics-based applications. Keywords Half-metallic ferromagnet (HMF) electrodes · Magnetic tunnel junction (MTJ) · Parallel configuration (PC) · Antiparallel configuration (APC) · Tunnel magnetoresistance (TMR)  Alok Kumar Singh alok.kh95@gmail.com Sudhanshu Choudhary sudhanshu@nitkkr.ac.in; hellosudhanshubit@gmail.com 1 School of VLSI Design and Embedded Systems, National Institute of Technology, Kurukshetra, India 1 Introduction Spintronics, a new classification of electronics, capitalizes on the spin property of an electron in addition to its charge property, providing a future solution for high operating speed and low power consumption in electronic devices. The major use of spintronics-based devices has been in the field of information storage, and magnetoresistive ran- dom access memory (MRAM) is the best example of it. A giant magnetoresistance (GMR) device has been pro- posed based on a graphene nanosheet and has been studied experimentally leading to remarkable results in informa- tion storage [1]. A typical magnetic tunnel junction (MTJ) consists of two ferromagnetic/half-metallic ferromagnetic (HMF) electrodes with a tunnel barrier (thin) connecting the two electrodes. The resistance of the MTJ device depends on the relative orientation of the electron spin for the two ferromagnetic/HMF electrodes. In an MTJ device, if the magnetic orientation of electrons for the two electrodes is similar, i.e., either spin up or spin down, then it is termed parallel configuration (PC), and if the orientations are oppo- site with a phase difference of 180 ◦ , then it is known as antiparallel configuration (APC) [2]. The spin direction of the ferromagnetic materials can be changed by applying an external magnetic field. This results in the different elec- tronic properties for the different magnetic orientations of the electrodes. MTJ devices till date have used Y 2 O 3 , MgO, and Al 2 O 3 as a thin tunnel barrier, but due to the presence of defects and interdiffusion of materials, their use is limited [3, 4]. Graphene shows many exciting properties as a half-integer quantum Hall effect at room temperature [5], long-range ballistic transport with ten times greater mobility than that of silicon (Si), and finite bandgap due to quantum con- finement. These outstanding properties of graphene can be