Magneto-Structural Coupling in the Antiferromagnetic Copper Orthoniobate Cu 3 Nb 2 O 8

High Resolution Image Download MS PowerPoint Slide The structural, vibrational, electronic, optical, and magnetic properties of triclinic Cu 3 Nb 2 O 8 were investigated through a combined experimental and theoretical approach. Synchrotron X-ray diffraction confirmed the centrosymmetric P 1̅ structure, while Raman and infrared spectroscopy enabled the identification of the vibrational modes, supported by lattice-dynamics calculations. Density functional theory calculations indicated that the electronic states near the conduction band minimum are mainly associated with Cu 3d orbitals, whereas the valence band is predominantly composed of O 2p states. Magnetic susceptibility measurements revealed two antiferromagnetic transitions at T 1 = 26.09 K and T 2 = 24.15 K. Temperature-dependent Raman analyses evidenced anomalous phonon behavior between 20 and 60 K, indicating spin-phonon interactions associated with the magnetic ordering process. In addition, magnetocaloric measurements exhibited a magnetic entropy variation centered near the Néel temperature, reinforcing the presence of magnetoelastic coupling in Cu 3 Nb 2 O 8 . These results provide a comprehensive description of the interplay between lattice dynamics, electronic structure, and magnetic ordering in this copper orthoniobate system.