Femtosecond spectroscopy in the far and near field for the investigation of the magnetization-reversal dynamics

• Applicant: Professor Dr. Paul Fumagalli
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2002 to 2006
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5374038

Polarized near-field optical microscopy has a high potential as a virtually non-interacting method for the investigation of thin-film magnetism. This is done by means of the local Kerr or Faraday effect yielding a lateral resolution well below the classical diffraction limit. Relying on our long-term experience with magneto-optic near-field microscopy, one goal of this proposal is to establish a new microscopic method with high lateral resolution which is capable to measure the dynamics of magnetization-reversal processes in the femtosecond regime by pump-probe experiments in the near field. A second goal is to investigate the nature of the exchange coupling of local spins in a model Heisenberg-magnet system. The model systems to be looked at are the Europium chalcogenides EuX, where EuS is the ferromagnetic compound to be prepared most easily as a thin film. The exchange coupling between the non-overlapping local 4f moments is believed to be due to a virtual Rudermann-Kittel-Kasuya-Yoshida exchange of virtually excited electrons in the 5d band. By performing two color pump-probe experiments, the dynamics of the transient magnetization will be investigated. A transient magnetization is induced by optically exciting 3p-electrons into the 5d band yielding a real occupation in the conduction 5d band. The strong exchange coupling between 4f and 5d electrons in combination with RKKY-like coupling within the 5d band should lead to a spontaneous alignment of the 4f spins well above the Curie temperature of EuS of 16.5 K. In this way, we hope to be able to verify directly the 30 year-old theory by Kasuya.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1133: Ultrafast magnetization processes