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Magnetic properties in perovskite titanates ATiO3‐δ (A = Ca, Sr, Ba) were investigated before and after arc melting. Crystal structure analysis was conducted by powder synchrotron X‐ray diffraction with Rietveld refinements. Quantitative chemical element analysis was carried out by X‐ray photoelectron spectroscopy. Magnetic measurements were conducted by vibrating sample magnetometer and X‐ray magnetic circular dichroism (XMCD). The magnetic properties are found to be affected by impurities of 3d elements such as Fe, Co, and Ni. Depending on the composition and crystal structure, the occupation of the magnetic ions in perovskite titanates is selectively varied, which is interpreted to be the origin of the different magnetic behaviors in arc‐melted perovskite titanates ATiO3‐δ (A = Ca, Sr, Ba). In addition, both formation of oxygen vacancies and the reduction of Ti4+ to Ti3+ during arc‐melting also play a role as proven by XMCD. Nevertheless, preferential site occupation of magnetic impurities is dominant in the magnetic properties of arc‐melted perovskite ATiO3‐δ (A = Ca, Sr, Ba). [ABSTRACT FROM AUTHOR]

Transition-metal dichalcogenides (TMDCs) are an aspiring class of materials with unique electronic and optical properties and potential applications in spin-based electronics. Here, terahertz emission spectroscopy is used to study spin-to-charge current conversion (S2C) in the TMDC NbSe2 in ultrahigh-vacuum-grown F|NbSe2 thin-film stacks, where F is a layer of ferromagnetic Fe or Ni. Ultrafast laser excitation triggers an ultrafast spin current that is converted into an in-plane charge current and, thus, a measurable THz electromagnetic pulse. The THz signal amplitude as a function of the NbSe2 thickness shows that the measured signals are fully consistent with an ultrafast optically driven injection of an in-plane-polarized spin current into NbSe2. Modeling of the spin-current dynamics reveals that a sizable fraction of the total S2C originates from the bulk of NbSe2 with the opposite, negative sign of the spin Hall angle as compared to Pt. By a quantitative comparison of the emitted THz radiation from F|NbSe2 to F|Pt reference samples and the results of ab initio calculations, it is estimated that the spin Hall angle of NbSe2 for an in-plane polarized spin current lies between -0.2% and -1.1%, while the THz spin-current relaxation length is of the order of a few nanometers. [ABSTRACT FROM AUTHOR]

Efficient focusing of X‐rays is essential for high‐resolution X‐ray microscopy. Diffractive X‐ray optics called kinoforms offer the highest focusing efficiencies in theory. However, they have long remained unavailable due to their challenging nanofabrication. Recently, various X‐ray optic geometries including kinoforms have been realized using 3D laser lithography at near‐infrared wavelengths. As the smallest features (period) of the kinoform determines the resolving power, there is a natural drive to find ways to fabricate kinoforms with ever smaller features. Here, a custom‐built 3D laser lithography setup with an excitation wavelength of 405 nm is used, which allows to half the smallest period of the kinoforms compared to previous work. A 40% improvement in scanning transmission X‐ray microscopy image resolution, that is, a cutoff resolution of 145 nm, and an efficiency of 7.6% at 700 eV is achieved. A reconstructed pixel size of 18.5 nm, reaching the limit imposed by the design of the microscopy set‐up, is demonstrated through ptychographic imaging of a magnetic sample which has a strongly reduced contrast mechanism. Moreover, X‐ray lenses manufactured by 405 nm 3D laser lithography have the potential to become much less expensive than X‐ray lenses made by other means. [ABSTRACT FROM AUTHOR]

Herein, a ferrimagnetic manganese zinc ferrite (Mn0.5Zn0.5Fe2O4) film with a thickness of 200 nm is prepared without a buffer layer on strontium titanate (001) (SrTiO3) using pulsed laser deposition. Its magnetic properties are investigated using superconducting quantum interference device (SQUID), X‐ray absorption spectroscopy with subsequent X‐ray magnetic circular dichroism (XMCD) and magneto‐optic Kerr effect (MOKE). Hysteresis loops derived from SQUID exhibits bulk‐like properties. This can further be confirmed by bulk‐like XMCD spectra. In remanent magnetization, an in‐plane magnetization with basically no out‐of‐plane component is found. The magnetic moments derived by the sum rule formalism from the XMCD data are in good agreement to the magnetization observed by SQUID and MOKE. XMCD as well as MOKE reveal an in‐plane angular fourfold magnetic anisotropy with the easy direction along [110] for (Mn0.5Zn0.5)Fe2O4 on SrTiO3. The element‐specific magnetic moments from XMCD show a stronger contribution of Fe to the anisotropy than of Mn and distinct contributions of the orbital moments. [ABSTRACT FROM AUTHOR]

Due to the tunable magnetic exchange interactions between nearest neighbor moment carriers by exchange linker length or metal ions, metal–organic frameworks (MOFs) in general, and MOF‐74 in particular, have promising magnetic properties for novel industrial applications such as magnetic switchers, sensors, and multifunction devices in molecular spintronics. Hence, MOF‐74‐M [M2(C8H2O6)] (M = Fe, Co, Ni) possessing a 1D channel is prepared and experimentally examined to describe its diverse magnetic properties, depending on the metal cluster used. By exchanging the metal ion (Fe, Co, and Ni) in the metal cluster, the magnetic state of MOF‐74 is changed from ferromagnetic or antiferromagnetic to superparamagnetic. This phenomenon can be also confirmed by alternating current (AC)/direct current (DC) magnetic susceptibility and field‐dependent magnetization. Therefore, the intrinsic magnetic properties of MOF‐74‐M such as blocking temperature, Néel temperature, and interaction energy between metals in magnetic susceptibility tests can be elucidated. Moreover, the superparamagnetic behavior in this system is also observed in M–H curves and magnetic dynamics as single‐chain magnets. It is believed that MOF‐74‐M can be utilized for applications in which superconducting materials are required (e.g., memory‐storage devices). [ABSTRACT FROM AUTHOR]

Abstract: Focusing X‐rays to single nanometer dimensions is impeded by the lack of high‐quality, high‐resolution optics. Challenges in fabricating high aspect ratio 3D nanostructures limit the quality and the resolution. Multilayer zone plates target this challenge by offering virtually unlimited and freely selectable aspect ratios. Here, a full‐ceramic zone plate is fabricated via atomic layer deposition of multilayers over optical quality glass fibers and subsequent focused ion beam slicing. The quality of the multilayers is confirmed up to an aspect ratio of 500 with zones as thin as 25 nm. Focusing performance of the fabricated zone plate is tested toward the high‐energy limit of a soft X‐ray scanning transmission microscope, achieving a 15 nm half‐pitch cut‐off resolution. Sources of adverse influences are identified, and effective routes for improving the zone plate performance are elaborated, paving a clear path toward using multilayer zone plates in high‐energy X‐ray microscopy. Finally, a new fabrication concept is introduced for making zone plates with precisely tilted zones, targeting even higher resolutions. [ABSTRACT FROM AUTHOR]

FeMn/Co thin-films, a purely metallic exchange-bias system, were prepared on (100)-oriented MgO single crystals. The layers were grown by molecular beam epitaxy (MBE). The crystalline and magnetic properties could be tuned by using sputtered Pt buffer layers deposited at variable temperatures. A transition of the crystalline orientation from (111)-terminated layers at lower deposition temperatures to (100)-terminated layers at temperatures higher than 950 K was established and the impact on the magnetic sample properties was investigated. Here, the detailed sample preparation process is shown together with low energy electron diffraction (LEED), medium energy electron diffraction (MEED), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements revealing the samples structure and composition. The crystalline orientation of Pt was imprinted to the magnetic layer stack and clearly influenced the exchange-bias (EB) and coercive field ( HC) as shown by superconducting quantum interference device (SQUID) and magneto-optical Kerr effect (MOKE) measurements. Furthermore, a correlation between the crystallite size and the temperature dependent magnetic properties could be identified. [ABSTRACT FROM AUTHOR]

A kinoform lens is a highly efficient photonic device capable of focusing a wide range of electromagnetic radiation. Unfortunately, its realization without the need of any approximation remained elusive for a very long time. A direct, simple and precise fabrication method was still missing. Here, an efficient preparation scheme is presented for the first time. Two kinoform lenses made out of polycrystalline gold and nano‐crystalline PdSi, are successfully fabricated, thoroughly characterized and tested for their ultimate focusing performances at soft X‐ray energies. The fabrication is made possible by means of gray‐scale direct‐write ion beam lithography. A first ever 2D imaging is carried out via scanning transmission X‐ray microscopy achieving resolutions down to 60 nm. The diffraction efficiency is measured to be 77% to 89% of the theoretical value and is only limited by the strong absorption at the soft X‐ray energy range. The impact of materials selection on the final quality of the lens is emphasized. The overall results enable the production of almost perfect kinoform profiles with high precision. This opens unprecedented perspectives for the focusing of soft and hard X‐rays at very high efficiencies and paves the way toward new applications in a wider energy range. [ABSTRACT FROM AUTHOR]

Fresnel zone plates (FZPs) recently showed significant improvement by focusing soft X-rays down to ∼10 nm. In contrast to soft X-rays, generally a very high aspect ratio FZP is needed for efficient focusing of hard X-rays. Therefore, FZPs had limited success in the hard X-ray range owing to difficulties of manufacturing high-aspect-ratio zone plates using conventional techniques. Here, employing a method of fabrication based on atomic layer deposition (ALD) and focused ion beam (FIB) milling, FZPs with very high aspect ratios were prepared. Such multilayer FZPs with outermost zone widths of 10 and 35 nm and aspect ratios of up to 243 were tested for their focusing properties at 8 keV and shown to focus hard X-rays efficiently. This success was enabled by the outstanding layer quality thanks to ALD. Via the use of FIB for slicing the multilayer structures, desired aspect ratios could be obtained by precisely controlling the thickness. Experimental diffraction efficiencies of multilayer FZPs fabricated via this combination reached up to 15.58% at 8 keV. In addition, scanning transmission X-ray microscopy experiments at 1.5 keV were carried out using one of the multilayer FZPs and resolved a 60 nm feature size. Finally, the prospective of different material combinations with various outermost zone widths at 8 and 17 keV is discussed in the light of the coupled wave theory and the thin-grating approximation. Al2O3/Ir is outlined as a promising future material candidate for extremely high resolution with a theoretical efficiency of more than 20% for as small an outermost zone width as 10 nm at 17 keV. [ABSTRACT FROM AUTHOR]

Swimming microorganisms have been shown to be useful for the propulsion of microrobotic devices due to their self‐powered motion. Up to now, mainly bacteria, e.g., magnetotactic bacteria (MTB), are investigated as biohybrid microrobots. But biocompatibility studies of MTB regarding medical utilizations are still lacking. Moreover, MTB require special culture conditions for their stability, which also might limit their usage for biomedical applications. Herein, a cytocompatible, highly motile microswimmer is presented from a microalga, Chlamydomonas reinhardtii, which has the capacity to carry large loads. C. reinhardtii cells are magnetized by incorporating terbium. The following analyses reveal an induced magnetic moment of a magnetized C. reinhardtii cell of 1.6 × 10−11 emu, comparable to its counterparts used as magnetotactic microrobots. The magnetized algae are able to align to the field lines of an applied uniform magnetic field, guiding them to swim in a directional motion. In addition, C. reinhardtii cells and human cells show mutual biocompatibility, indicating that the algae cells are noncytotoxic. Furthermore, the magnetized microalgae reported here are easy to track in the human body by luminescence imaging tools due to their innate autofluorescence performance and photoluminescence of the incorporated Tb3+. Thus, terbium‐incorporated microalgae are promising candidates for magnetically steerable biohybrid microrobots. Magnetotactic microalgae are facilely generated by accumulation of magnetic terbium ions inside the living cells. The fast swimming algae can be controlled magnetically, they align passively to magnetic field lines and swim actively towards the magnets. They have fluorescence properties due to the lanthanide terbium and show mutual biocompatibility with mammal cells. The reported magnetotactic microalgae display promising candidates for microrobotic devices. [ABSTRACT FROM AUTHOR]

A correction to the article related to X-rays with multilayer Fresnel zone plates fabricated by atomic layer deposition is presented.