Hierarchical molecular spin excitations in a geometrically frustrated magnet

Geometrically frustrated magnets exhibit a spin-liquid-like state until much below the temperature of magnetic energy in systems instead of magnetic long-range order. A spin molecule phenomenon is one of the representative states. In a magnetically ordered phase that is supposed to eliminate frustration, however, we recently discovered several modes of molecular spin excitation levels with different shapes and energies by inelastic neutron scattering. We discuss the roots of spin molecules from this new result. (author)