Ab Initio Study of Hexagonal Boron Nitride as the Tunnel Barrier in Magnetic Tunnel Junctions

Abstract

Two-dimensional hexagonal boron nitride (h-BN) is studied as a tunnel barrier in magnetic tunnel junctions (MTJs) as a possible alternative to MgO. The tunnel magnetoresistance (TMR) of such MTJs is calculated as a function of whether the interface involves the chemi- or physisorptive site of h-BN atoms on the metal electrodes, Fe, Co, or Ni. It is found that the physisorptive site on average produces higher TMR values, whereas the chemisorptive site has the greater binding energy but lower TMR. It is found that alloying the electrodes with an inert metal-like Pt can induce the preferred absorption site on Co to become a physisorptive site, enabling a higher TMR value. It is found that the choice of physisorptive sites of each element gives more Schottky-like dependence of their Schottky barrier heights on the metal work function.

Reduced Fermi Level Pinning at Physisorptive Sites of Moire-MoS2/Metal Schottky Barriers

“…Compared to MoS 2 , h-BN has very strong B–N electron-pair bonding. This creates a more extreme variation of pinning factor S between the chemi- and physisorptive sites for h-BN/metal interfaces, from S ∼ 1 to 0.25. , On the other hand, for MoS 2 , each sulfur atom with three neighboring Mo atoms already has multicenter bonding rather than electron-pair bonding as in h-BN. Thus, at MoS 2 /metal interfaces, sulfur atoms can easily bond to metal atoms with the multicenter bonding character.…”

“…Here, the chemisorptive site is the N on top of the metal site, whereas rotating the h-BN lattice to form the (√3×√3) orientation provides a physisorptive site with both B and N lying off-center and with a much larger interlayer spacing, 21 − 24 as schematically shown in Figure 1 e. The slope factor of h-BN contacts was found to be dramatically different for each site, S ∼ 0.26 for the chemisorptive site, while S ∼ 1 for the physisorptive site. 22 …”

“…The slope factor of h-BN contacts was found to be dramatically different for each site, S ∼ 0.26 for the chemisorptive site, while S ∼ 1 for the physisorptive site. 22 Heavier 2D materials such as MoS 2 show a similar but lessextreme behavior. The SBH depends mainly on the metal work function 12 and less on interfacial bond lengths.…”

Quantum Phase Transition in the Spin Transport Properties of Ferromagnetic Metal-Insulator-Metal Hybrid Materials

“…However, the spin polarized current that is generated from pMTJs is highly susceptible to anisotropies, such as those induced by the tunnel barrier material and the applied field. Although several concerted efforts have been focused on the study of different 2D materials as the tunnel barrier layer in pMTJs [ 12 , 13 , 14 ], neither the nature of the underlying magnetoelectric coupling mechanisms nor the roles of the tunnel barrier layer in the transmitted spin current are well-understood. Gaining insights into such phenomena is a crucial first step toward achieving a lower energy-delay product performance [ 15 ].…”

Giant tunneling magnetoresistance in two-dimensional magnetic tunnel junctions based on double transition metal MXene ScCr2C2F2

“…[3][4][5][6] Furthermore, much efforts have been put into the relevant research for MTJs since the tunneling magnetoresistance (TMR) effect was rstly discovered in Fe/Ge/Co multilayer lms. [7][8][9] Herein, the TMR ratio is regarded as one of the most important factors for estimating the performance of MTJs. To enhance the TMR ratio, an effective method involves employing intrinsic magnetic materials with high spin polarizabilities as the electrode material.…”