Microstructure and magnetic properties of Co nanoparticles in ion-implanted Al2O3

Ion implantation and thermal processing can be used to create a variety of single-element or compound ferromagnetic nanocrystals embedded in dielectric host materials. This approach leads to the formation of nanocomposites with several attractive characteristics for potential applications in magnetic data storage media. A number of problems must be addressed before such applications can be realized in practice, however. One difficulty lies in the exercise of sufficiently fine control over the magnetic and microstructural properties of interest. Here, we show that Co nanocrystals produced by the ion implantation of Al2O3 can be formed either as spheroidal or well faceted single-crystal precipitates, depending on the synthesis conditions. Subsequent ion irradiation of the nanoparticles can alter the microstructure and internal chemistry of the particles as well as that of the host matrix, thereby providing a means of increasing the coercive field of the Co nanoparticles by almost two orders of magnitude.