Magnetic order and interactions in ferrimagnetic Mn3Si2Te6

The magnetism in Mn3Si2Te6 has been investigated using thermodynamic measurements, first-principles calculations, neutron diffraction, and diffuse neutron scattering on single crystals. These data confirm that Mn3Si2Te6 is a ferrimagnet below TC ≈78 K. The magnetism is anisotropic, with magnetization and neutron diffraction demonstrating that the moments lie within the basal plane of the trigonal structure. The saturation magnetization of ≈1.6μB/Mn at 5 K originates from the different multiplicities of the two antiferromagnetically aligned Mn sites. First-principles calculations reveal antiferromagnetic exchange for the three nearest Mn-Mn pairs, which leads to a competition between the ferrimagnetic ground state and three other magnetic configurations. The ferrimagnetic state results from the energy associated with the third-nearest-neighbor interaction, and thus long-range interactions are essential for the observed behavior. Diffuse magnetic scattering is observed around the 002 Bragg reflection at 120 K, which indicates the presence of strong spin correlations well above TC. These are promoted by the competing ground states that result in a relative suppression of TC and may be associated with a small ferromagnetic component that produces anisotropic magnetism below ≈330K.