High-Density Non-magnetic Cobalt in Cobalt Thin Films

Abstract

Volume contraction or higher density of any bulk material is usually obtained by placing the material under high-pressure conditions. For materials in the form of thin films, a compressed (higher density) state may be obtained during growth without the necessity of any external pressure. Here, we present cobalt thin films, grown on silicon, which show the formation of high-density layers within the film. Normal cobalt is ferromagnetic. Theoretical calculations have shown that cobalt can be non-magnetic when its density increases beyond a specific value. Formation of this high-density (HD) non-magnetic (NM) state of cobalt in cobalt thin films has been revealed and confirmed via various experiments. The non-magnetic state of cobalt is of great interest. Ferromagnetism and superconductivity are known to be antagonistic. When ferromagnetic normal cobalt becomes non-magnetic, it raises the possibility of being a superconductor. Indeed both experiments and theory have shown the high-density non-magnetic cobalt to be a superconductor. The cobalt films have grown in a trilayer structure—HDNM Co/normal Co/HDNM Co. Thus, it is a self-organized superconductor (S)/ferromagnet (F)/superconductor (S) hybrid structure. S/F/S hybrid structures have potential applications in areas like spintronics and quantum information technology.