Magnetic properties of MnAs nanocrystals embedded in GaAs

A phenomenological model for explaining the magnetic properties of MnAs nanocrystals embedded in GaAs is proposed. It is shown that experimental data of DC magnetization as a function of temperature, obtained according to zero-field-cooled and field-cooled protocols, can be understood assuming a transition of the system from a low temperature state in which very slow dynamics is observed (frozen state) to a high-temperature state in which dynamics is fast (quasi superparamagnetic state).