A device and to a method of producing a device, wherein the method includes, inter alia, providing a substrate and generating at least two mutually spaced-apart cavities within the substrate. In accordance with the invention, each cavity has a depth of at least 50 μm. The cavities are filled up with magnetic particles, wherein the magnetic particles enter into contact with one another at points of contact, and wherein cavities are formed between the points of contact. At least some of the magnetic particles are connected to one another at their points of contact, specifically by coating the magnetic particles, wherein the cavities are at least partly penetrated by the layer produced in the coating process, so that the connected magnetic particles form a magnetic porous structure.