Disentangling magnetic order on nanostructured surfaces

We present a synchrotron-based x-ray scattering technique which allows disentangling magnetic properties of heterogeneous systems with nanopatterned surfaces. This technique combines the nanometer-range spatial resolution of surface morphology features provided by grazing incidence small angle x-ray scattering and the high sensitivity of nuclear resonant scattering to magnetic order. A single experiment thus allows attributing magnetic properties to structural features of the sample; chemical and structural properties may be correlated analogously. We demonstrate how this technique shows the correlation between structural growth and evolution of magnetic properties for the case of a remarkable magnetization reversal in a structurally and magnetically nanopatterned sample system.

Figure 1

Illustration of the GINSAXS principle by means of a sample with faceted surface: (a) A heterogeneous Fe film is grown on a nanofaceted substrate by sputter deposition under non-normal incidence. (b) The 2D scattering pattern is the same for both nonresonantly and resonantly scattered photons; photons detected in the left (right) crystal truncation rod (CTR) carry information on the Fe film regions on the R-plane (S-plane) facets. (c) Using a time-resolving detector to record only resonant photons, nuclear resonant time spectra are taken at the left and right CTR, evidencing the different magnetic properties of the Fe film on the R-plane and S-plane facets, respectively.

Figure 2

(a) Exemplary NRS time spectra and corresponding fits (red) for the Fe film regions on R- and S-plane facets, respectively, in an applied magnetic field of $B_{\mathrm{ext}}=200$ mT. The differences in the beat patterns evidence unequal magnetization orientations. (b) Azimuthal (in-plane) and polar (out-of-plane) magnetization orientation in R-plane and S-plane film regions as extracted from fits of the NRS time spectra. Solid lines are guides to the eye. (c) A cross-sectional transmission electron micrograph (left) and a top-view sketch (right) of the sample, with arrows indicating the out-of-plane and in-plane components of the magnetization vectors relative to external magnetic field.

Figure 3

Exemplary nonresonant GISAXS patterns and corresponding simulations for two stages of Fe deposition onto the faceted substrate. The dashed lines indicate the specular scattering plane. The GISAXS patterns are dominated by the tilted crystal truncation rods (CTRs) originating from the surface facets. The different periods of the intensity modulations along the CTRs result from the different thicknesses of the Fe film on the R-plane and S-plane facets, respectively. Labels state the nominally deposited Fe film thickness ${\mathrm{d}}_{\mathrm{nom}}$ and the thicknesses of the film regions ${\mathrm{d}}_{\mathrm{R}}$ and ${\mathrm{d}}_{\mathrm{S}}$ as obtained from simulations.

Figure 4

Sequences of NRS time spectra (top to bottom) with corresponding fits (red) for film regions on R-plane and S-plane facets at subsequent stages of Fe deposition. The development of the characteristic beat pattern evidences the successive transition from a nonmagnetic to a ferromagnetic state in the R-plane and S-plane regions. Strength and orientation of magnetic moments in the film regions on R-plane and S-plane facets are indicated by black and white arrows, respectively.