Abstract

Single-particle excitations in a quasi-one dimensional ferromagnet spin chain placed in a nonuniform magnetic field with a large gradient are considered. In a magnetic field with a constant gradient there occurs a dynamic localization of spin waves and an equidistant energy level spectrum like the Wannie–Zeeman «ladder» is formed. A similar phenomenon is known for an electron in a periodic potential and a weak electric field. In a semi-infinite chain the spin excitation spectrum is bounded from below; a gradual evolution from spin waves in a nonuniform magnetic field to Wannie–Zeeman states occurs with increasing energy. An infinite chain in nonuniform magnetic field is considered when a constant magnetic field is applied in the x < 0 region and a linearly increasing one is applied in the x > 0 region. In this case a set of localized Wannie–Zeeman-like states appears above the spin wave zone, whose spectrum becomes equidistant at the high energies. Possibilities of experimental observation of Bloch oscillations in spin systems are discussed.

PACS: 75.10.Pq Spin chain models;
PACS: 75.30.Ds Spin waves;
PACS: 75.40.Gb Dynamical properties.

Key words: spin waves, spin chains, low dimension magnetic, Bloch oscillations.