Magnetic phase transitions in nanoclusters and nanostructures

The review includes theoretical models and experimental results on magnetic phase transitions in magnetic nanoclusters and nanostructures. It is shown, that nanoclusters with the sizes of a few or tens nanometers possess the critical sizes (similarly to critical temperatures Curie or Neel), less of which cluster or cluster nanostructure loses magnetic ordering due to the first order magnetic phase transitions (by the jump). Change of the character of magnetic phase transitions (first-to-second order), the reduction of Curie or Neel points and the finding of critical sizes of nanoclusters has been observed on ferric oxides and hydroxides in solid state and matrix nanostructures.