Investigation of Octahedral Distortions and Their Influence on Magnetic and Phononic Excitations in a Columbite-Structured Niobate

Columbite-structured NiNb2O6 features magnetic Ni2+ ions arranged in chains along the crystallographic c-axis, where ferromagnetic superexchange dominates, while weaker antiferromagnetic interactions occur between chains. This leads to a quasi-one-dimensional magnetic behavior with orthorhombic anisotropy that, although subtle at high temperatures, becomes significant at low temperatures, influencing spin dynamics and magnetic excitations. Single-ion anisotropy causes splitting of crystal-field levels and affects the orientation of ordered magnetic moments within the ac plane, aligned along local easy axes. Inelastic neutron scattering provides a unique opportunity to probe the magnetic excitation spectrum and it s coupling to lattice vibrations driven by octahedral distortions. This investigation will deepen understanding of the interplay between low-dimensional magnetism, anisotropy, and spin phonon coupling in NiNb2O6, a representative columbite-type magnetic oxide.