Geometric and Magnetic Structures of K2ReI6 as an Antiferromagnetic Insulator with Ferromagnetic Spin-Canting Originated from Spin−Orbit Coupling

We present the results of a crystallographic analysis, magnetic characterization including neutron powder diffraction, and theoretical assessment of K2ReI6 prepared using solvent reactions. K2ReI6 crystallizes in the space group P21/n with an inversion center. Magnetic measurements of K2ReI6 sample indicate dominant antiferromagnetic coupling with a Curie–Weiss temperature of θW = −63.3(1) K, effective magnetic moment ∼2.64 μB/Re but show a weak ferromagnetism ordered at ∼24 K. Neutron powder diffraction indicates long-range order of the Re spins below 24 K, with an ordered magnetic moment of 2.2(1) μB/Re at 1.5 K. Therefore, a canted antiferromagnetic structure is concluded. The electronic structures using first-principles calculations suggest that the antiferromagnetic model of K2ReI6 yields the lowest total energy and opens a band gap with ∼1.0 eV width, which is consistent with the UV–vis–NIR optical measurements. After including the spin–orbit coupling (SOC) into the calculation, the band degeneracies slightly shift without influencing the band gap. The results imply that K2ReI6 is an antiferromagnetic insulator with weak ferromagnetic spin-canting resulting from strong SOC-entangled ground state S = 3/2.