A ferromagnetic (porous silicon/metal)-nanocomposite with an additional paramagnetic behavior

Investigations on a nanostructured metal/semiconductor hybrid system show a novel magnetic behavior with a spin-magnetism at low magnetic fields and an additional paramagnetic term at higher fields. The system is composed of a porous silicon (PS) matrix formed by anodization of an n-type silicon wafer with electrochemically deposited metal-structures. The morphology of the membrane is tuneable by the anodization conditions, but the metal deposition within the channels of the template can also be modified by changing the galvanic parameters of the metal-loading procedure. Both the variation of the template (pore-diameter, pore-distance) and the adjustment of the metal-filling (spatial distribution along the channels, shape of the precipitations) enable selective modification of the magnetic properties of the nanocomposite system. The geometry of the precipitated metal-structures, which vary between spheres, ellipsoids and wires as well as their mutual arrangement, determines the magnetic behavior (coercivity, squareness) at magnetic fields beneath the saturation magnetization of the deposited metal. At higher magnetic fields a subsequent non-saturating paramagnetic term occurs which is due to orbital currents in silicon. Both properties together, the spin-magnetism and the additionally appearing orbital magnetism form a novel magnetic behavior, characteristic for the introduced hybrid nanocomposite.