Rice University physicists have discovered a new type of magnetic excitation, termed "spin excitons," in nickel molybdate crystals, which consist of two parts nickel, three parts molybdenum, and eight parts oxygen. Unlike traditional spin waves that ripple through magnets, these spin excitons propagate as coherent waves, showcasing unusual properties. Neutron scattering experiments revealed that the two outermost electrons from nickel ions cancel each other out, forming a spin singlet, defying the expectation that such a system shouldn’t exhibit magnetism. Further experiments identified two families of propagating waves characterized by differing energies, influenced by the crystal field effects that alter electron spin alignments. These excitations occur even at elevated temperatures, where the material typically loses its magnetic properties, resembling a unique interaction between different types of excitons. Significantly, both types of nickel atoms in the crystal form triangular lattices, leading to magnetic frustrations that challenge traditional magnetic alignment theories. This research, published in Nature Communications, advances the understanding of magnetic phenomena in complex materials, with implications for future studies in quantum materials and spintronics. The experiments were supported by various research foundations and conducted in collaboration with several institutions.
