Tuning the properties of magnetic thin films by interaction with periodic nanostructures

The most important limitation for a significant increase of the areal storage density in magnetic recording is the superparamagnetic effect. Below a critical grain size of the used CoCrPt exchange-decoupled granular films the information cannot be stored for a reasonable time (typically ten years) due to thermal fluctuations arbitrary flipping of the magnetization direction. An alternative approach that may provide higher storage densities is the use of so-called percolated media, in which defect structures are imprinted in an exchange-coupled magnetic film. Such percolated magnetic films are investigated in the present work. We employ preparation routes that are based on (i) self-assembly of Au nanoparticles and (ii) homogeneous size-reduction of self-assembled polystyrene particles. On such non-close-packed nanostructures thin Fe films or Co/Pt multilayers are grown with in-plane and out-of-plane easy axis of magnetization. The impact of the particles on the magnetic switching behavior is measured by both integral magnetometry and magnetic microscopy techniques. We observe enhanced coercive fields while the switching field distribution is broadened compared to thin-film reference samples. It appears possible to tailor the magnetic domain sizes down to the width of an unperturbed domain wall in a continuous film, and moreover, we observe pinning and nucleation at or close to the imprinted defect structures

The Effect of Obstructive Sleep Apnea and Continuous Positive Airway Pressure Therapy on Skeletal Muscle Lipid Content in Obese and Nonobese Men.

Obstructive sleep apnea (OSA), independently of obesity (OBS), predisposes to insulin resistance (IR) for largely unknown reasons. Because OSA-related intermittent hypoxia triggers lipolysis, overnight increases in circulating free fatty acids (FFAs) including palmitic acid (PA) may lead to ectopic intramuscular lipid accumulation potentially contributing to IR. Using 3-T-1H-magnetic resonance spectroscopy, we therefore compared intramyocellular and extramyocellular lipid (IMCL and EMCL) in the vastus lateralis muscle at approximately 7 am between 26 male patients with moderate-to-severe OSA (17 obese, 9 nonobese) and 23 healthy male controls (12 obese, 11 nonobese). Fiber type composition was evaluated by muscle biopsies. Moreover, we measured fasted FFAs including PA, glycated hemoglobin A1c, thigh subcutaneous fat volume (ScFAT, 1.5-T magnetic resonance tomography), and maximal oxygen uptake (VO2max). Fourteen patients were reassessed after continuous positive airway pressure (CPAP) therapy. Total FFAs and PA were significantly (by 178% and 166%) higher in OSA patients vs controls and correlated with the apnea-hypopnea index (AHI) (r ≥ 0.45, P < .01). Moreover, IMCL and EMCL were 55% (P < .05) and 40% (P < .05) higher in OSA patients, that is, 114% and 103% in nonobese, 24.4% and 8.4% in obese participants (with higher control levels). Overall, PA, FFAs (minus PA), and ScFAT significantly contributed to IMCL (multiple r = 0.568, P = .002). CPAP significantly decreased EMCL (-26%) and, by trend only, IMCL, total FFAs, and PA. Muscle fiber composition was unaffected by OSA or CPAP. Increases in IMCL and EMCL are detectable at approximately 7 am in OSA patients and are partly attributable to overnight FFA excesses and high ScFAT or body mass index. CPAP decreases FFAs and IMCL by trend but significantly reduces EMCL

Single-crystalline YIG nanoflakes with uniaxial in-plane anisotropy and diverse crystallographic orientations

We study Y3Fe5O12 (YIG) nanoflakes that we produce via mechanical cleaving and exfoliation of YIG single crystals. By characterizing their structural and magnetic properties, we find that these YIG nanoflakes have surfaces oriented along unusual crystallographic axes and uniaxial in-plane magnetic anisotropy due to their shape, both of which are not commonly available in YIG thin films. These physical properties, combined with the possibility of picking up the YIG nanoflakes and stacking them onto nanoflakes of other van der Waals materials or pre-patterned electrodes or waveguides, open unexplored possibilities for magnonics and for the realization of novel YIG-based heterostructures and devices.Comment: 13 pages, 4 figure

On the interpretation of time-resolved surface reflectivity measurements during the laser annealing of Si thin films

Time-resolved surface reflectivity measurements of nanosecond pulse laser-annealed Si thin films are compared to the simultaneously measured reflectivity of the interface between the film and glass substrate. In the case of complete melting of the film the liquid is supercooled. The measurements of the interface reflectivity show that the resolidification process starts at the interface. The resolidification at the surface occurs after an energy-dependent delay of up to 40 ns. The analysis of the data shows that during this delay time the surface temperature may be increased by the latent heat released at the interface. This reheating effect of the surface, which has not been considered yet demands for a careful interpretation of surface reflectivity measurements

Surface-plasmon-enhanced multiple-photon photoemission from Ag and Al films

Photoemission from Ag and Al films, mediated by surface plasmons, was studied using a Q-switched Nd:YAG laser (where YAG denotes yttrium aluminum garnet) as a light source in the attenuated-total-reflection configuration. Both the intensity dependence of the photoemission yield and the pulse width of the photoemission signal show for metal one-, two-, and three-photon processes for the laser wavelengths λ=355, 532, and 1064 nm, respectively

Mit Kapillarkräften zu Nanostrukturen : wie man die Selbstorganisation von Kolloidkügelchen für die Submikrometer-Lithographie nutzen kann

Nanostrukturen sind zurzeit in aller Munde, da man von ihnen neuartige physikalische und chemische Eigenschaften erwartet. Zur Erzeugung solcher Strukturen mit GroBen von wenigen hundert Nanometern und darunter werden ganz unterschiedliche Lithographyeverfahren eingesetzt. Dabei sind meist aufwandige Apparaturen notwendig, um grotlere nanostrukturierte Bereiche zu erhalten. Im Folgenden stellen wir einen alternativen, technisch einfachen Ansatz vor, bei dem ein durch Kapillarkrafte induzierter, selbstorganisierter Prozess fiir die Herstellung von Nanostrukturen ausgenutzt wird

Nanosecond time-resolved reflectivity determination of the melting of metals upon pulsed laser annealing

Thin metal films (Cu, Au, Ni) on quartz glass were illuminated with nanosecond pulses of a frequency doubled Nd:YAG laser (λ = 532 nm). The transient reflectivity behaviour was probed at the wavelength 633 nm, where these metals exhibit Drude-like optical behaviour: the reflectivity decreases with temperature in the solid and in the liquid state as well as at the solid-liquid phase transition. It is shown that nanosecond time-resolved reflectivity measurements can be used to determine the melting of these metal surfaces due to the reflectivity difference between the solid and the liquid phase

Size-Dependent Self-Organization of Colloidal Particles on Chemically Patterned Surfaces

A study of the self-organization of colloidal particles during the evaporation of particle solutions on chemically patterned surfaces is presented. On a surface with hydrophilic and hydrophobic regions, colloidal particles form compact structures on the hydrophilic sites. When a colloidal solution containing a mixture of particles with a variation in size is used, the number density of each type of particle deposited on the hydrophilic islands after evaporation decreases with increasing particle size. This makes it possible to produce a concentration gradient of the particles on islands of different sizes. It is shown that this technique could allow for particle separation

Photoswitching Affinity and Mechanism of Multivalent Lectin Ligands

Multivalent receptor-ligand binding is a key principle in a plethora of biological recognition processes. Immense binding affinities can be achieved with the correct spatial orientation of the ligands. Accordingly, the incorporation of photoswitches, that can be used to reversibly change the spatial orientation of molecules, into multivalent ligands is a means to alter the binding affinity and possibly also the binding mode of such ligands. We report a divalent ligand for the model lectin wheat germ agglutinin (WGA) containing an arylazopyrazole photoswitch. This switch, that has been recently introduced as an alternative to the more commonly used azobenzene moiety, is characterized by almost quantitative E / Z photoswitching in both directions, high quantum yields, and high thermal stability of the Z isomer. The ligand was designed in a way that only one of the isomers is able to bridge adjacent binding sites of WGA leading to a chelating binding mode. Photoswitching induces an unprecedentedly high change in lectin binding affinity as determined by isothermal titration calorimetry (ITC). Furthermore, additional dynamic light scattering (DLS) data suggest that the binding mode of the ligand changes from chelating binding of the E isomer to crosslinking binding of the Z isomer.publishe