Introduction to nanomagnetism

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magnetic scales

Scale of size that goes from macroscopic down to nanoscopic sizes. The unit of this scale is the number of magnetic moments in a magnetic system (roughly corresponding to the number of magnetic atoms). At macroscopic sizes, a magnetic system is described by magnetic domains that are separated by domain walls. Magnetization reversal occurs via nucleation, propagation, and annihilation of domain walls (hysteresis loop on the left). When the system size is of the order of magnitude of the domain wall width or the exchange length, the formation of domain walls requires too much energy. Therefore, the magnetization remains in the so-called single-domain state, and the magnetization reverses by uniform rotation or nonuniform modes (middle). SMMs are the final point in the series of smaller and smaller units from bulk matter to atoms and magnetization reverses via quantum tunneling (right).

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