13:30 〜 15:30
▲ [24p-P01-12] High magnetoresistance of hexagonal boron nitride-graphene heterostructure-based MTJ through excited-electron transmission
キーワード：2D materials, graphene-hBN heterostructure
An ab-initio study was done of a few-layers hexagonal boron nitride (hBN) and hBN-graphene heterostructure sandwiched between Ni(111) layers. Spin-polarized density functional theory calculations and transmission probability calculations were conducted on Ni(111)/nhBN/Ni(111) with n = 2, 3, 4, and 5 as well as on Ni(111)/hBN-Gr-hBN/Ni(111). Slabs with magnetic alignment in an anti-parallel configuration (APC) and parallel configuration (PC) were considered. The pd-hybridizations at both the upper and lower interfaces between the Ni slabs and hBN stabilized the system. The Ni/nhBN/Ni magnetic tunnel junction (MTJ) was found to exhibit a high tunneling magnetoresistance (TMR) ratio at E-E_F = 0.34 eV for n = 2 and 0.34 eV for n > 2, which are slightly higher than the Fermi energy. The observed shifting of this high TMR ratio originates from the transmission of electrons through the surface states of the d_z^2-orbital of Ni atoms at interfaces which are hybridized with the p_z-orbital of N atoms. In the case of n > 2, the proximity effect causes an evanescent wave, contributing to decreasing transmission probability but increasing the TMR ratio. The highest TMR ratio was observed when Ni/3hBN/Ni MTJ was considered. However, TMR ratio and transmission probability were increased by replacing the unhybridized hBN layer of the Ni/3hBN/Ni MTJ with graphene, thus becoming Ni/hBN-Gr-hBN/Ni. A TMR ratio as high as ~1200% was observed at E-E_F = 0.34 eV. A specific device design is proposed, as shown in Fig. 1.b, which has a new reading mechanism by exploiting the high TMR observed at E-E_F = 0.34 eV.