Lattices of ferromagnetic granules - theory and experiments
As a result of technology development, magnetic nanostructures from an object
of academic examinations are transmuted into a subject of
experimental analysis and become elements of electronic devices. In this
talk, the term ``nanostructure" relates only to regular lattices of
single-domain ferromagnetic nanogranules. Exchange interaction establishes
ferromagnetic ordering of magnetic moments inside granules while the
intergranule interaction is purely dipole. Granules shaped as ellipsoids
of revolution or their limiting types are considered.
The examples of similar systems are diversiform. Among them are regular
structures of magnetic granules viewed as the medium, perspective for
increasing magnetic storage density. Patterned media of that sort are
usually rectangular lattices of single-domain prolate magnetic granules.
Magnetic insulator nanocomposite is another example. The electrical
conductivity of such a system is associated with tunnel electron
transitions between granules whose probability is determined by mutual
orientation of magnetic moments of the adjacent granules. The third example
is a thin film of a ferromagnetic metal on a single-crystal substrate.
The long-range ferromagnetic order appearing in such films is associated
with the specific film growth mode: it resembles a lattice of ellipsoidal
Ground state, magnetic phase diagram, phase transitions are studied for
two and three-dimensional lattices of ferromagnetic granules with dipole
intergranule interaction. Conclusions of the theory compare with results
of a series of experiments.