Towards wafer scale inductive determination of magnetostatic and dynamic parameters of magnetic thin films and multilayers

We investigate an inductive probe head suitable for non-invasive characterization of the magnetostatic and dynamic parameters of magnetic thin films and multilayers on the wafer scale. The probe is based on a planar waveguide with rearward high frequency connectors that can be brought in close contact to the wafer surface. Inductive characterization of the magnetic material is carried out by vector network analyzer ferromagnetic resonance. Analysis of the field dispersion of the resonance allows the determination of key material parameters such as the saturation magnetization MS or the effective damping parameter Meff. Three waveguide designs are tested. The broadband frequency response is characterized and the suitability for inductive determination of MS and Meff is compared. Integration of such probes in a wafer prober could in the future allow wafer scale in-line testing of magnetostatic and dynamic key material parameters of magnetic thin films and multilayers

Imaging and phase-locking of non-linear spin waves

Non-linear processes are a key feature in the emerging field of spin-wave based information processing and allow to convert uniform spin-wave excitations into propagating modes at different frequencies. Recently, the existence of non-linear magnons at half-integer multiples of the driving frequency has been predicted for Ni80Fe20 at low bias fields. However, it is an open question under which conditions such non-linear spin waves emerge coherently and how they may be used in device structures. Usually non-linear processes are explored in the small modulation regime and result in the well known three and four magnon scattering processes. Here we demonstrate and image a class of spin waves oscillating at half-integer harmonics that have only recently been proposed for the strong modulation regime. The direct imaging of these parametrically generated magnons in Ni80Fe20 elements allows to visualize their wave vectors. In addition, we demonstrate the presence of two degenerate phase states that may be selected by external phase-locking. These results open new possibilities for applications such as spin-wave sources, amplifiers and phase-encoded information processing with magnons

Tunneling magneto thermo power in magnetic tunnel junction nanopillars

We study the tunneling magneto thermo power (TMTP) in CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars. Thermal gradients across the junctions are generated by a micropatterned electric heater line. Thermo power voltages up to a few tens of \muV between the top and bottom contact of the nanopillars are measured which scale linearly with the applied heating power and hence with the applied temperature gradient. The thermo power signal varies by up to 10 \muV upon reversal of the relative magnetic configuration of the two CoFeB layers from parallel to antiparallel. This signal change corresponds to a large spin-dependent Seebeck coefficient of the order of 100 \muV/K and a large TMTP change of the tunnel junction of up to 90%.Comment: Revised version containing additional data and analyis. 13 pages, 3 figure

Application of imaging to the atmospheric Cherenkov technique

Turver and Weekes proposed using a system of phototubes in the focal plane of a large reflector to give an air Cherenkov camera for gamma ray astronomy. Preliminary results with a 19 element camera have been reported previously. In 1983 the camera was increased to 37 pixels; it has now been routinely operated for two years. A brief physical description of the camera, its mode of operation, and the data reduction procedures are presented. The Monte Carlo simultations on which these are based on also reviewed

Observations of the Crab Nebula at energies 4.10(11)

Since the development of gamma-ray astronomical telescopes, the Crab Nebula has been a prime target for observations. From 100 to 1000 MeV, the pulsar PSR0531 is the dominant source with a light-curve similar to that seen at lower energies; there is also some evidence for longterm amplitude variations but none for emission from the Nebula itself. In the very high energy gamma-ray region there have been reported detections of pulsed emission with longterm time variations from minutes to months. Recently a pulsed flux has been reported that resisted over a long time interval. The detection of a flux from the Nebula at the 3 sigma level at energies of 3x1011eV was reported; there was no evidence of periodic emissions on any time scale during the three years of observations. A new measurement of very high energy gamma rays from the Crab Nebula is reported using the imaging system on the Whipple Observatory 10m reflector

Effective exchange interaction for terahertz spin waves in iron layers

The exchange stiffness is a central material parameter of all ferromagnetic materials. Its value controls the Curie temperature as well as the dynamic properties of spin waves to a large extent. Using ultrashort spin current pulses we excite perpendicular standing spin waves (PSSW) in ultrathin epitaxial iron layers at frequencies of up to 2.4 THz. Our analysis shows that for the PSSWs the observed exchange stiffness of iron is about 20% smaller compared to the established iron bulk value. In addition, we find an interface-related reduction of the effective exchange stiffness for layers with the thickness below 10 nm. To understand and discuss the possible mechanisms of the exchange stiffness reduction we develop an analytical one-dimensional model. In doing so we find that the interface induced reduction of the exchange stiffness is mode dependent

Search for gamma-rays from M31 and other extragalactic objects

Although the existence of fluxes of gamma-rays of energies 10 to the 12th power eV is now established for galactic sources, the detection of such gamma-rays from extragalactic sources has yet to be independently confirmed in any case. The detection and confirmation of such energetic photons is of great astrophysical importance in the study of production mechanisms for cosmic rays, and other high energy processes in extragalactic objects. Observations of m31 are discussed. It is reported as a 10 to the 12th power eV gamma-ray source. Flux limits on a number of other extragalactic objects chosen for study are given

New Developments in the SCIAMACHY Level 2 Ground Processor Towards Version 7

SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric ChartographY) aboard ESA’s environmental satellite ENVISAT observed the Earth’s atmosphere in limb, nadir, and solar/lunar occultation geometries covering the UV-Visible to NIR spectral range. It is a joint project of Germany, the Netherlands and Belgium and was launched in February 2002. SCIAMACHY doubled its originally planned in-orbit lifetime of five years before the communication to ENVISAT was severed in April 2012, and the mission entered its post-operational phase. In order to preserve the best quality of the outstanding data recorded by SCIAMACHY, data processors are still being updated. This presentation will highlight three new developments that are currently being incorporated into the forthcoming Version 7 of ESA’s operational Level 2 processor: 1. Tropospheric BrO, a new retrieval based on the scientific algorithm of (Theys et al., 2011). This algorithm had originally been developed for the GOME-2 sensor and was later adapted for SCIAMACHY. 2. Improved cloud flagging using limb measurements (Liebing, 2015). Limb cloud flags are already part of the SCIAMACHY L2 product. They are currently calculated employing the scientific algorithm developed by (Eichmann et al., 2015). Clouds are categorized into four types: water, ice, polar stratospheric and noctilucent clouds. High atmospheric aerosol loadings, however, often lead to spurious cloud flags, when aerosols had been misidentified as clouds. The new algorithm will better discriminate between aerosol and clouds. It will also have a higher sensitivity w.r.t. thin clouds. 3. A new, future-proof file format for the level 2 product based on NetCDF. The data format will be aligned and harmonized with other missions, particularly GOME and Sentinels. The final concept for the new format is still under discussion within the SCIAMACHY Quality Working Group