Theoretical anatomy of altermagnetic α-MnTe from magnetism to triple-resistance states

α-MnTe is among the earliest discovered altermagnets with experimental evidence of A-type antiferromagnetic order above room temperature and spin-split bands. Here, we conduct a theoretical investigation of its magnetism based on the general symmetry-adaptive tensorial spin model, which not only confirms a Néel temperature of 340 K induced by the dominant 1st and 3rd nearest-neighbor Heisenberg exchanges, but also the hexagonal planar Néel vector polarization of the ground state due to both the single-ion and the two-ion anisotropies. The 6-fold rotation symmetry along z prohibits an in-plane easy axis when only considering rank-2 and rank-4 interactions, revealing the continuous ground state degeneracy. Subsequently, we show that the triple-resistance states can be realized by adopting MnTe as the barrier in the sandwiched magnetic tunnel junctions. By deliberately matching the Brillouin zone-resolved spin transport of both the barrier and the electrode, tunneling magnetoresistance up to ~5300% is obtained. Our work not only provides a fine database of the magnetism and transmission for MnTe, but also sheds light on the application in high-density spintronic memory devices.