Superparamagnetism and the Spin-glass like properties

The superparamagnetism and the spin-glass like properties, which has wide applications in the technological point of view. Superparamagnetism is a finite size effect since the particle anisotropy is generally proportional to its volume and has important applications in the thermal and time stability of the bits written in recording media. Spin glass property is also has some relevant applications in the memory devices. Spin glass is a substance in which electron spins in a random direction below TG. It contains many metastable states separated by the potential barrier of KBoltzTG. Once it falls into one of the metastable states, it cannot have a more stable state at a thermal energy below TG. However the addition of some external field, for example, light irradiation, will turn the metastable state into a more stable state. This feature is exclusively used in optical magnetic memory devices. However generally, in spin glass, the TG is very low, far below room temperature. To utilize a spin glass as an actual magnetic memory device, a spin glass with a higher TG at least approximately near room temperature is desired.