Magnetic phase transition in the low-dimensional compound BaMn ₂Si₂O₇

The structural and magnetic properties of BaMn₂Si ₂O₇ have been investigated. The magnetic susceptibility and specific heat, measured using single crystals, suggest that the quasi-one-dimensional magnetism originating from the loosely coupled Mn2 ⁺ chain carrying S=5/2 is present at high temperatures, which is similar to the other quasi-one-dimensional barium silicates, BaM ₂Si₂O₇ (M: Cu and Co). The Néel temperature (T_N∼26 K) is high compared to the magnetic interaction along the chain (J=-6 K). Neutron powder diffraction study has revealed that the magnetic structure is long ranged with antiferromagnetic arrangement along the chain (c) direction and ferromagnetic arrangement along the a and b axes. Detailed structural analysis suggests that the interchain interaction via Mn-O-Mn bond along the a axis is relatively large, which makes the system behave more two-dimensionally in the ac plane and enhances T _N.