Disentangling magnetic order on nanostructured surfaces

Nanopatterned magnetic materials are of considerable interest for both academic research and industrial application. We present a novel technique, combining Nuclear Resonant Scattering (NRS) [1] and GISAXS [2], which allows disentangling the magnetic properties of distinct structural units in a nanopatterned system. The underlying idea is to exploit the fact that the nuclear resonant signal (carrying the magnetic information) undergoes the same scattering in q-space as the electronic signal (carrying the structural information). Thus, photons scattered resonantly from different structural units of the sample are separated due to the sample morphology and can be detected at different positions in the scattering pattern. To demonstrate this principle, we fabricated a 57Fe thin film sample with alternating thick and thin stripe-like regions, i.e. with heterogeneous structural and magnetic properties, which vary periodically on the nm-scale. We investigated the sample in-situ during growth (beamline ID18, ESRF) and studied its response to external magnetic fields ex-situ (beamline P01, PETRA III). During film growth, we observed the onset of ferromagnetic ordering first in the thicker regions, then in the thinner regions. Upon applying an external magnetic field, the magnetic moments in thick and thin regions are displaced from the easy axis of magnetization to different extents [3, 4]. Our experiments thus show that nuclear resonant GISAXS is a sensitive method for obtaining information about the magnetic state of individual nm-scaled parts of a magnetically heterogeneous sample.

[1] R. Röhlsberger, Springer Tracts in Modern Physics 208 (2004)
[2] G. Renaud, R. Lazzari, and F. Leroy, Surface Science Reports 64 (2009) 255
[3] D. Erb, Ph.D. thesis, University of Hamburg (2015)
[4] manuscript in preparation