Recently, it became possible to image in three dimensions magnetic textures having dimension of 100 nm or even less. The joint teams of the Laboratoire Albert Fert in Palaiseau and the SEXTANTS beamline scientists, helped by colleagues from the Helmholtz-Zentrum Berlin, the University of Augsburg and the Max Planck Institute for Chemical Physics of Solids in Dresden, used a peculiar holography technique called HERALDO, allowing different projection of a sample containing “cocoons” to be acquired. Digitally combining these projections delivers a 3D map of the 3D magnetization inside the sample.
Sub-micronic three dimensional (3D) magnetic textures, notably the ones having a peculiar topology and chirality, are attracting a renew attention these last few years, partly thanks to the progresses in the imaging techniques. Among them, some are topologically non-trivial, meaning that they cannot be continuously deformed into a uniform state. Their non-trivial topology gives rise to a number of physical effects, such as the skyrmion Hall effect or the topological Hall effect. Understanding the chiral interactions allowing their stabilization and imaging their 3D internal structure has enabled the control of such effects. Among the imaging techniques stand in good position the ones based on soft X-ray imaging: the photons energy is tuned at an energy at which the absorption depends on the magnetic state of the sample, providing magnetic contrast with high spatial resolution.
At SOLEIL, on the SEXTANTS beamline, HERALDO measurements were performed. HERALDO is a form of holography measurements which uses slits instead of holes as reference sources. The advantage of the slit is notably that it allows the sample to be tilted in the X-ray beam and hence record different projection of the sample and its magnetic state. Using a recursive algorithm, after a fairly complex treatment of images including nm-precision alignment, the 3D magnetization is reconstructed in 3D.
Read more on the SOLEIL website
Image: Reconstructed magnetization texture. The out-of-plane magnetization mz of the bottommost layer is represented in red (mz < 0) and blue (mz > 0). Zero mz isosurfaces appear as ghosty gray surfaces and a pair of cocoons (about 150 nm in diameter) are highlighted with the in-plane magnetization direction displayed as colored arrows.