Insights to unusual antiferromagnetic behavior and exchange coupling interactions in Mn23C6

Abstract

Abstract We report the structural, mechanical and electromagnetic properties of the intermetallic compound Mn23C6. The bulk Mn23C6 sample was synthesized using high temperature high pressure quenching method (HTHPQM), and investigated in detail by x-ray diffraction, electron microscope, magnetization and electrical resistivity measurements, etc. First-principles calculation based on density functional theory ab intio simulation was carried out to calculate the bonding and electromagnetic properties of Mn23C6. Based on our experimental and simulated results, the Mn23C6 in this work is single phase of a faced-centered cubic structure with space group Fm-3m (No. 225). Determined by SEM and TEM, the bulk sample consists of monocrystal Mn23C6 crystals with 2–15 μm grain sizes, it is the quick quenching method in the synthesizing process that brings such small crystal grain size. Archimedes method gives its density of 7.14 g/cm3, 95.74% of its theoretically calculated density 7.458 g/cm3. Owing to the abundant Mn 3d electrons and a framework of strongly linked Mn atoms in Mn23C6, the electrical conductivity is up to 8.47 × 10−4 Ω⋅m, which shows that Mn23C6 is a good conductor. Our magnetic susceptibility analyses reveal a magnetization peak in the M–T curve at 104 K, combined with the M–H curve and Curie–Weiss law, this peak usually means the transformation between paramagnetic and antiferromagnetic orders. To gain an insight into the mechanism of the magnetic phase transition, we calculated the magnetic properties, and the results show that different from normal antiferromagnetic order, the magnetic orders in Mn23C6 consist of three parts, the direct ferromagnetic and antiferromagnetic exchange coupling interactions between Mn atoms, and the indirect antiferromagnetic super-exchange interaction between Mn and C atoms. Therefore, we reveal that the Mn23C6 is a complex magnetic competition system including different magnetic orders and interactions, instead of the normal long-range antiferromagnetic order.