A method for influencing and/or detecting magnetic particles in a region of action, magnetic particles and the use of magnetic particles is disclosed, which method comprises the steps of: -introducing magnetic particles into a region of action, - generating a magnetic selection field having a pattern in space of its magnetic field strength such that a first sub-zone having a low magnetic field strength and a second sub-zone having a higher magnetic field strength are formed in the region of action -changing the position in space of the two sub-zones in the region of action by means of a magnetic drive field so that the magnetization of the magnetic particles change locally, -acquiring signals, which signals depend on the magnetization in the region of action, which magnetization is influenced by the change in the position in space of the first and second sub-zone; wherein the magnetic particles comprise a core region and a shell region, the core region comprising a magnetic material, wherein the magnetic material of the core region is provided as a mainly metallic material of comparably high saturation magnetization, wherein the shell region comprises mainly a metal oxide material or a nobel metal material.