High Electrical Conductance in Magnetic Emission Junction of Fe₃GeTe₂/ZnO/Ni Heterostructure via Selective Spin Emission through ZnO Ohmic Barrier

The insulator is essential for magnetic tunneling junction (MTJ) that increases magnetoresistance (MR) by decoupling magnetization directions between two ferromagnets. However, wide bandgap tunnel barrier blocks the thermionic emission of electrons, significantly reducing electrical conductance through MTJ. Here, a magnetic emission junction (MEJ) is demonstrated for the first time using an Fe₃GeTe₂ (FGT)/ZnO/Ni heterostructure with very high electrical conductance. The conduction band of ZnO (electron affinity 4.6 eV) aligns with Fermi levels (E_F) of FGT (4.47 eV) and Ni (4.58 eV) ferromagnets and forms an Ohmic barrier, enabling free spin-electron emission through ZnO barrier and high electrical conductance. In contrast to the typical positive MR in MTJ by majority spin tunneling, negative MR is observed in FGT/ZnO/Ni MEJ. The minority spin electrons of Ni, with maximum states near the E_F, are dominantly emitted to FGT over the ZnO barrier, while majority spin electrons of Ni, with maximum states below the E_F, are blocked by it. In the FGT/FGT/ZnO/Ni heterostructure, the MR ratio is further increased by combining positive and negative MR at the MTJ (FGT/FGT) and MEJ (FGT/ZnO/Ni), respectively. As a result, FGT-MEJ exhibits 10-1000 orders higher conductance than other 2D-MTJs, while MR ratio remains similar to other 2D-MTJs.