Magnetic order and interactions in ferrimagneticMn3Si2Te6

The magnetism in Mn₃Si₂Te₆ has been investigated using thermodynamic measurements, first principles calculations, neutron diffraction and diffuse neutron scattering on single crystals. These data con rm that Mn3Si2Te6 is a ferrimagnet below T_C 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 1.6 B/Mn at 5K 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. Di use magnetic scattering is observed around the 002 Bragg reflection at 120 K, which indicates the presence of strong spin correlations well above T_C . These are promoted by the competing ground states that result in a relative suppression of T_C , and may be associated with a small ferromagnetic component that produces anisotropic magnetism below ≈ 330 K.