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Influence of Domain Wall Pinning on the Dynamic Behavior of Magnetic Vortices Soft magnetic, micron-sized thin-film structures with magnetic vortices are intriguing systems that may one day be used in ultrafast computer memories. In such systems, the otherwise in-plane magnetization turns perpendicular to the plane at the center of the vortex, forming the vortex core. Because such a core has two possible polarizations (up or down) and can be switched between these two states by a small alternating magnetic field, it could serve as a memory bit in future magnetic memory devices. However, these magnetic structures often contain numerous imperfections such as domain wall pinning sites, which have to be taken into account for the practical application of such systems. To study how these defects affect the dynamics of magnetic vortices, researchers from Belgium, Germany, and the United States investigated square-shaped and disk-shaped thin-film structures with artificially introduced imperfections in the form of nanometer-sized holes. They used time-resolved scanning transmission x-ray microscopy (STXM) at Beamline 11.0.2 to determine the frequency at which these vortices vibrate (their eigenfrequency). The imperfections were found to cause a higher vibrational frequency in square-shaped structures, but did not influence the disk-shaped structures. Knowledge of the frequency is crucial for vortex-based memories, since the electric signal for writing data needs to be precisely tuned to it. Read more…
Publication about this research: A. Vansteenkiste, J.D. Baerdemaeker, K.W. Chou, H. Stoll, M. Curcic, T. Tyliszczak, G. Woltersdorf, C.H. Back, G. Schütz, and B.V. Waeyenberge, “Influence of domain wall pinning on the dynamic behavior of magnetic vortex structures: Time-resolved scanning x-ray transmission microscopy in NiFe thin film structures,” Phys. Rev. B 77, 144420 (2008). |
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Photons on Demand: A New Bunch-Kicking Mode at the ALS Contacts: Greg Portmann, Peter Fischer, and Dave Robin
The ALS has a difficult task to fulfill: provide the best beam to a huge variety of experiments. It is not surprising the demands are as diverse as the experiments. Time-resolved research, which is scientifically highly rewarded, often requires two-bunch operation. However, two-bunch is only provided twice a year at the ALS (~ 20 days total). This is because the majority of researchers do not require this timing structure for their experiments and are therefore dissatisfied with the much-reduced flux. This dilemma might be resolved for some experiments by a recently developed technique called pseudo single bunch. By using a pulsed magnet, one bunch in the train, the so-called camshaft bunch, is vertically kicked onto a different orbit from the rest of the bunches. If that bunch can be spatially separated in the beamline, then some beamlines can be using a multibunch beam while others are using only a single bunch. This simultaneous use would be in effect “two synchrotrons in one.”
The full-field high-resolution soft x-ray microscope at Beamline 6.1.2 recently demonstrated that it can use this new mode to study fast spin dynamics in nanostructured magnetic elements. This scientific area is of the utmost relevance both for fundamental and technological reasons (in view of the quest to make magnetic memory devices not only smaller but faster). In addition, during a recent test experiment on Beamline 6.1.2 the camshaft bunch was displaced vertically by about 500 μm. By adjusting the x-ray optics in the microscope to this new source position, the magnetic contrast in a ferromagnetic GdFe alloy thin film switched on and off synchronously with the switching of the fast kicker, thus demonstrating that switching between single and multibunch imaging is possible without requiring any changes in the storage ring.
Left: With the single bunch being kicked vertically, a clear magnetic domain structure can be seen in a ferromagnetic GdFe film. Right: When the bunch kicker is switched off, the domains clearly disappear. Other experiments could also benefit from the new scheme. One remaining question is the degree to which experiments running in the conventional multibunch mode are sensitive to the displaced camshaft bunch. However, by installing multiple fast magnets, it would be possible to isolate the perturbation to specific sections of the accelerator, thereby avoiding areas that are particularly sensitive to asymmetric beam profiles. |
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The x-ray microscopy community came together in Zurich, Switzerland, from July 21 to July 25 for the 9th International Conference on X-Ray Microscopy Another highlight of the conference was the presentation of the memorial Werner Meyer-Ilse award to ALS scientist Anne Sakdinawat (see below) for her development of modified zone plates for phase contrast and high depth of focus applications and to Pierre Thibault (Paul Scherrer Institute) for his pioneering work in coherent diffraction imaging and ptychography. |
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CXRO Scientist and ALS User Anne Sakdinawat Wins 2008 Werner Meyer-Ilse Award
Anne Sakdinawat has pursued a wide array of techniques that will improve x-ray microscopy, including phase and resolution enhancements to zone-plate-based microscopy, massively parallel redundant array holography, and lensless diffractive imaging. Her paper for the conference, “Specialized Diffractive Optics for Contrast Resolution Enhancement,” presents experimental results and optics fabrication methods to improve contrast and resolution for x-ray imaging studies. These include the development of diffractive lenses that combine a Fresnel zone plate with a specific phase structure, allowing imaging and filtering to be performed within a single lens, enhancing contrast or resolution while keeping alignment simple. Click here
Top, L-R. SEM images of regular zone plate, charge 1 spiral zone plate, and charge 2 spiral zone plate. Bottom, L-R. Corresponding images of a uniformly illuminated, 1-micron-diameter, circular pinhole showing edge enhancement with the spiral zone plate (A. Sakdinawat and Y. Liu, Opt. Lett. 32 2635, 2007). |
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UEC Corner: 2008 Users’ Meeting; the UEC Needs New Members
The UEC Needs New Members. After the Users’ Meeting, you will have the chance the elect three new members to the UEC, who will replace the representatives whose terms expire at the end of this year. Please contact me (hohldag@stanford.edu) if you are interested in being a member. We are specifically looking for candidates from the area of structural and molecular biology since this group is not represented at this time. A list of current UEC members can be found on the UEC Web site. |
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On Friday, August 15, nineteen incoming freshman students from the Physics, Astronomy, and Earth and Planetary Sciences departments at UC Berkeley visited the ALS to get an inside view of an active research facility. The students are participants in the Compass Project
Mike Martin leads a tour of Compass Project students. |
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__________________________________________________ Bulletin Board As the ALS nears readiness for top-off operation, here is the planned schedule: Top-Off Testing. Some testing of top-off on approved beamlines will occur during accelerator physics shifts beginning in October 2008 and extending through the end of the calendar year. We expect that the majority of beamlines will be approved for testing in October and all by the end of the first week in January. Date for First Full Top-Off Operation. Assuming successful tests and the approval of all beamlines, the ALS will begin to operate in top-off mode on a routine basis in January 2009. New General ALS Requirement: Closed-Toe Shoes The ALS safety advisory on the use of personal protective equipment (PPE) at the ALS was revised on August 12, 2008. Among other updates to this advisory, it is now mandatory that all staff, users, and visitors wear closed-toe shoes on the experimental floor, accelerator area, and all peripheral lab areas. Go to the PPE Advisory Web page to read this user advisory in its entirety. __________________________________________________ |
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For the user runs from July 15 to August 17: Beam reliability*: 91.2%; Completion**: 85.9%. This period included the nine-day period of 2-bunch user operations (from August to August 10). Injection difficulties that began around 1:00 a.m. on August 4 (during the 2-bunch run) resulted in a loss of about eight hours of user beam time. Questions about beam reliability should be sent to David Richardson. Requests for special operations use of the “scrubbing” shift should be sent to Rick Bloemhard (ALS-CR@lbl.gov, x4738) by 1:00 p.m. Friday.
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At the International X-Ray Microscopy meeting (XRM 2008) in Zurich, Switzerland, Anne Sakdinawat was presented with the prestigious Werner Meyer-Ilse Award (along with co-recipient Pierre Thibault of the Paul Scherrer Institute). The award is presented every third year for contributions to the development of x-ray microscopy. Anne was honored “for the development of modified zone plates for phase contrast and high depth of focus applications.” She received her Ph.D. from the University of California, Berkeley, Department of Bioengineering; has been at Berkeley Lab’s Center for X-Ray Optics (CXRO) for the past five years; and is also a member of the ALS Users’ Executive Committee (UEC). Her research was performed at ALS 
2008 Users’ Meeting. The submission deadlines for the upcoming ALS Users’ Meeting (October 13–15) are approaching fast; therefore, I would like to bring to your attention two agenda items for which we need your contributions. One of the most exciting features of each ALS Users’ Meeting is the evening of the poster session, where everybody comes together and has a chance to see what their colleagues are doing and stimulating discussions can be overheard throughout. To make this session a success, we ask you to go to the 