Ba₉V₃Se₁₅: A novel compound with spin chains

In this work, a novel compound Ba₉V₃Se₁₅ with one-dimensional (1D) spin chains was synthesized under high-pressure and high-temperature conditions. It was systematically characterized via structural, magnetic, thermodynamic and transport measurements. Ba₉V₃Se₁₅ crystallizes into a hexagonal structure with a space group of P-6c2 (188) and the lattice constants of a = b = 9.5745(7) Å and c = 18.7814(4) Å. The crystal structure consists of face-sharing octahedral VSe₆ chains along c axis, which are trimeric and arranged in a triangular lattice in ab-plane. Ba₉V₃Se₁₅ is a semiconductor and undergoes complex magnetic transitions. In the zero-field-cooled (ZFC) process with magnetic field of 10 Oe, Ba₉V₃Se₁₅ sequentially undergoes ferrimagnetic and spin cluster glass transition at 2.5 K and 3.3 K, respectively. When the magnetic field exceeds 50 Oe, only the ferrimagnetic transition can be observed. Above the transition temperature, the specific heat contains a significant magnetic contribution that is proportional to T ^1/2. The calculation suggests that the nearest neighbor (NN) intra-chain antiferromagnetic exchange J ₁ is much larger than the next nearest neighbor (NNN) intra-chain ferromagnetic exchange J ₂. Therefore, Ba₉V₃Se₁₅ can be regarded as an effective ferromagnetic chains with effective spin-1/2 by the formation of the V(2)^(↓) V(1)^(↑) V(2)^(↓) cluster.