Semiclassical mechanics of a nonintegrable spin cluster

We study detailed classical-quantum correspondence for a cluster system of three spins with single-axis anisotropic exchange coupling. With autoregres sive spectral estimation, we find oscillating terms in the quantum density of states caused by classical periodic orbits: in the:slowly varying part o f the density of states we see signs of nontrivial topology changes happeni ng to the energy surface: as the energy is varied. Also, we can explain the hierarchy of quantum energy levels near the ferromagnetic and antiferromag netic states with Einstein-Brillouin-Keller quantization to explain large s tructures:and tunneling to explain small structures. [S0163-1829(99)03445-1 ].