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Volume 31, Number 8-9 (August 2005), p. 841-884
## Mesoscopic antiferromagnets: statics, dynamics, quantum tunneling
Institute of Magnetism of the National Academy of Sciences of Ukraine 36-b Vernadsky Ave. Kiev 03142, Ukraine
The static and dynamic, classic and quantum properties of antiferromagnets (AFM) are discussed basing on a unified approach. Special attention is concentrated on mesoscopic magnets, i.e., materials with characteristic scales of inhomogeneities of the order of atomic scales. Production of such materials, their study and application in many aspects specify contemporary physics. Among these materials are maghetic dots and their arrays, magnetic superlattices and clasters, high-spin molecules. The classical problems of antiferromagnet physics are also discussed (symmetrical analysis of AFM, orientational transitions, equations for spin dynamics), but they are introduced as far as they are useful for consideration of quantum and classical properties of mesoscopic AFM. To describe the spin dynamics of AFM, a spin Lagrangian is constructed, the form of which is consistent with the quantum-mechanical Hamiltonian. The effects of AFM dynamical symmetry reduction are taken into account, due to both classical reasons, for example, an external magnetic field, and partial decompensation of lattice spins. The latter effect is most important for mesoscopic AFM samples like ferritine particles. The influences of defects and surface effects on reorientational transitions in AFM are discussed in details. Such effects are essentially important for description of small particles of AFM and observed for magnetic superlattices with antiferromagnetic interaction between superlattice elements. Particular attention is paid to description of macroscopical quantum effects in mesoscopic AFM. On the basis of the spin Lagrangian obtained, new tunnel effects are described, for example, an oscillating dependence of tunneling probability on magnetic field. The quantum effects in magnetic systems with a nonuniform ground state are studied. These effects can be described as the tunneling process-induced changes of topological charges of various origin, characterising this state. PACS:75.50.Ee - Antiferromagnetics 75.45.+j - Macroscopic quantum phenomena in magnetic systems 75.50.Xx - Molecular magnets 75.50.Tt - Fine-particle systems; nanocrystalline materials |