This PhD project aims at designing, fabricating, and characterising new classes of three-dimensional (3D) periodic nanostructures featuring large magnetic permeabilities at infrared and optical frequencies – a property unknown from natural materials that allows for new aspects in optics. In particular, we intend to show for the first time evidence of the magnetic counterpart of the usual electric Brewster angle. The 3D samples should result from the metallisation of 3D dielectric templates fabricated by direct laser writing by using a silver chemical deposition process.