Lawrence Berkeley National Laboratory
Materials Science and Engineering
Recent progress in x-ray optics has pushed the lateral resolution of soft x-ray magnetic microscopy to below 15 nm. We have measured local magnetic hysteresis on a nanometer scale at the full-field x-ray microscope XM-1 at the Advanced... more
Recent progress in x-ray optics has pushed the lateral resolution of soft x-ray magnetic microscopy to below 15 nm. We have measured local magnetic hysteresis on a nanometer scale at the full-field x-ray microscope XM-1 at the Advanced Light Source in Berkeley, approaching fundamental length scales such as exchange lengths, Barkhausen lengths, and grain diameters. We have studied the evolution of magnetic domain patterns in a nanogranular CoCrPt film with a pronounced perpendicular magnetic anisotropy and revealed nanoscopic details associated with the granular film structure. From a quantitative analysis of the field-dependent magnetic domain patterns, we are able to generate local magnetic hysteresis map on a nanometer scale. Our findings indicate a significant variation of local coercive fields corresponding to the nanoscopic behavior of magnetic domains.
The combination of magnetic circular dichroism as a magnetic contrast mechanism and a transmission x-ray microscope allows imaging of magnetic structures with lateral resolutions down to 25 nm. Results on magneto-optical Tb 25 ͑Fe 75 Co... more
The combination of magnetic circular dichroism as a magnetic contrast mechanism and a transmission x-ray microscope allows imaging of magnetic structures with lateral resolutions down to 25 nm. Results on magneto-optical Tb 25 ͑Fe 75 Co 25 ͒ 75 layers system with thermomagnetically written bits of various sizes were obtained at the x-ray microscope XM-1 at the Advanced Light Source in Berkeley, CA. The results prove the thermal stability of the bits in the recording process. Furthermore the capability of soft x-ray microscopy with respect to the achievable lateral resolution, element specificity and sensitivity to thin magnetic layers is demonstrated. The potential of imaging in applied magnetic fields for both out-of-plane and in-plane magnetized thin magnetic films is outlined.
X-ray Magnetic Circular Dichroism (X-MCD), i.e. the change of the absorption of circular polarized Xrays for reversed sample magnetization amounts at the L 2,3edges of 3d transition metals up to 50% percent. This can be used to obtain in... more
X-ray Magnetic Circular Dichroism (X-MCD), i.e. the change of the absorption of circular polarized Xrays for reversed sample magnetization amounts at the L 2,3edges of 3d transition metals up to 50% percent. This can be used to obtain in energy-dispersive X-ray imaging techniques a considerable, element-specific magnetic contrast. On the other hand, with the transmission X-ray microscope (TXM) based on the zone-plate technique spatial resolutions of 30nm can be achieved. In this communication it is shown for the first time that the combination of the TXM with X-MCD provides a huge contrast and is therefore a powerful new method to visualize in a quantitative and elementspecific manner magnetic domains. Using soft X-rays with a wavelength of 1.7nm corresponding to the energy of the Fe L 3 -edge the variation of the shape and magnetization of domains in a magneto-optical GdFe layer system was studied with a lateral resolution of 60nm.
Topological magnetic states, such as chiral skyrmions, are of great scientific interest and show huge potential for novel spintronics applications, provided their topological charges can be fully controlled. So far skyrmionic textures... more
Topological magnetic states, such as chiral skyrmions, are of great scientific interest and show huge
potential for novel spintronics applications, provided their topological charges can be fully controlled. So far
skyrmionic textures have been observed in noncentrosymmetric crystalline materials with low symmetry
and at low temperatures. We propose theoretically and demonstrate experimentally the design of spin
textures with topological charge densities that can be tailored at ambient temperatures. Tuning the
interlayer coupling in vertically stacked nanopatterned magnetic heterostructures, such as a model system of
a Co/Pd multilayer coupled to Permalloy, the in-plane non-collinear spin texture of one layer can be
imprinted into the out-of-plane magnetised material. We observe distinct spin textures, e.g. vortices,
magnetic swirls with tunable opening angle, donut states and skyrmion core configurations. We show that
applying a small magnetic field, a reliable switching between topologically distinct textures can be achieved
at remanence.
potential for novel spintronics applications, provided their topological charges can be fully controlled. So far
skyrmionic textures have been observed in noncentrosymmetric crystalline materials with low symmetry
and at low temperatures. We propose theoretically and demonstrate experimentally the design of spin
textures with topological charge densities that can be tailored at ambient temperatures. Tuning the
interlayer coupling in vertically stacked nanopatterned magnetic heterostructures, such as a model system of
a Co/Pd multilayer coupled to Permalloy, the in-plane non-collinear spin texture of one layer can be
imprinted into the out-of-plane magnetised material. We observe distinct spin textures, e.g. vortices,
magnetic swirls with tunable opening angle, donut states and skyrmion core configurations. We show that
applying a small magnetic field, a reliable switching between topologically distinct textures can be achieved
at remanence.
Investigating magnetic properties of matter on the nanoscale is a very active area in modern solid-state physics 1-3 . Exciting phenomena, e.g. interlayer exchange coupling 4 or the giant magnetoresistance effect 5 , occur in... more
Investigating magnetic properties of matter on the nanoscale is a very active area in modern solid-state physics 1-3 . Exciting phenomena, e.g. interlayer exchange coupling 4 or the giant magnetoresistance effect 5 , occur in low-dimensional systems where characteristic length scales, i.e. magnetic exchange lengths, become relevant. Magnetic exchange lengths can be derived from intrinsic material parameters such as anisotropy (K) and exchange (A) constants, giving values <10 nm for typical magnetic materials, e.g. permalloy (Ni 80 Fe 20 ) or the hard magnetic system 6,7 Nd 2 Fe 14 B. Generally, the energetic ground state of a ferromagnetic system is not a single-domain state, but exhibits a characteristic microscopic magnetic domain structure that reflects the interplay between competing energies, such as anisotropy, exchange, Zeeman, and magnetostatic energies 8 . In order to understand the origin of macroscopic magnetic properties, this microstructure is the target of experimental 9-16 and theoretical studies . Moreover, the corresponding dynamics of the magnetic microstructure on a subnanosecond time scale is an emerging field, both for scientific and applied reasons, and numerous activities are currently being developed. Nanomagnetism is of utmost importance to current technological developments. The dramatic increase in magnetic storage density over the last decade , various applications of miniaturized magnetic sensor devices based on the giant magnetoresistance effect , and the development of spintronics, a new generation of computing technology , require a thorough understanding of magnetism on the nanometer scale. Spintronics considers the spin of an electron as an additional degree of freedom, which can be manipulated to obtain particular functionalities. Recent concepts for spintronic logical elements discuss domain walls , i.e. the intermediate region of spin inhomogeneity between two domains with opposite magnetization directions in nanowired elements. The magnetic nanoscale systems that exhibit the largest activity, both in fundamental and applied research, are multilayers and oxides , nanoparticles , nanostructures , semiconductors , multiferroic heterostructures , and spintronic materials . Several key questions in these systems depend on the dynamics of the magnetization and the associated magnetic microstructure 52-55 : • How does the magnetization reverse, i.e. how does it switch its orientation on a short length and fast time scale?
We report on the first demonstration of imaging microstructures with soft x-ray microscopy operating in reflection geometry. X-ray microscopy in reflection mode combines the high resolution available with x-ray optics, the ability to... more
We report on the first demonstration of imaging microstructures with soft x-ray microscopy operating in reflection geometry. X-ray microscopy in reflection mode combines the high resolution available with x-ray optics, the ability to image thick samples, and to directly image surfaces and interfaces. Future experiments with this geometry will include tuning the incident angle to obtain depth resolution. In combination with XMCD as magnetic contrast mechanism this mode will allow studies of deep buried magnetic interfaces.