The relative population of such frozen spins can be modulated by external physical parameters, such as the strength of the applied cooling field and the cycling history of magnetic field sweeps (training effect). A more complex change occurs when core-shell nanoparticles are aged under ambient conditions. Along with structural evolution from well-defined core-shell structures to particles containing multiple voids at the interface, there is a significant increase in the population of frozen spins, both of which affect the magnetic properties. More »
Researchers at Purdue University and Argonne have found that the magnetic exchange bias coupling between core and shell depends critically on the “frozen spins” that reside at the interface between the two different materials.