Problems of interacting quantum magnetic moments become exponentially complex with increasing number of particles. As a result, classical equations are often used to model spin systems and the validity of reduction from quantum classical problem should be analyzed. We formulate the analog of Ehrenfest’s theorem for a system of dipole-interacting magnetic moments which shows that the classical equations of motion for spin systems have identical form with the quantum equations for operators. Surprisingly, this correspondence, which is trivial for non-interacting spins, has never been formulated in an explicit form for dipole (or exchange) interacting spins. Clearly, the classical approach is very incomplete compared to the quantum one (e.g. the transitions between quantum states, the quantum entanglement, cannot be investigated with classical spins), but in some situations the classical simulations can provide a practical tool to study different macroscopic spin physics phenomena.
Another topic is related with phenomenon qualitatively similar to optical superradiation. The electromagnetic radiation emitted by an assembly of nano-entities by way of the feedback effect (like radiation damping) establishes the coherent dynamics. As the result, the relaxation time can become inversely proportional to the number of spins involved in the coherent motion.
I will also very briefly discuss magnetic properties of transition metal nanoparticles enclosed in graphitic carbon nanocages.
Professor Victor Henner, Perm State Univ. Russia, and Univ. of Louisville, KY
Host: James Sauls
Keywords: Physics, Astronomy, Condensed Matter