Gerd Much

Magnetic and magneto-optical properties of rare-earth transition-metal alloys containing Dy, Ho, Fe, Co

Amorphous rare‐earth transition‐metal alloys of composition REl−xTMx with RE=Dy, Ho; TM=Fe,Co and 0<x<1 and Dyl−x(Fe,Co)x were prepared by evaporation. The saturation magnetization, uniaxial anisotropy, coercivity, and Faraday rotation were investigated as a function of composition and temperature. Also, the spectral variation of the Kerr rotation was measured. The magnetization data indicate a strong dispersion of the RE moments due to randomly oriented local crystal field axes. The strong turndown of the Curie temperature for the Fe‐rich alloys suggests that an additional dispersion is present in the Fe subnetwork. The mean field theory was used to analyze the temperature variation of the magnetization yielding smaller TM spin values and exchange coupling constants as compared with those of the Gd and Tb analogs. The uniaxial anisotropy constant Ku for Dy‐Co based alloys was found to vary with the square of the Dy subnetwork magnetization as predicted by the random single‐ion theory. The anisotropy of D...

Analysis of lead oxide (PbO) layers for direct conversion X-ray detection

Lead oxide (PbO) is a candidate direct conversion material for medical X-ray applications. We produced various samples and detectors with thick PbO layers. X-ray performance data such as dark current, charge generation yield and temporal behavior were evaluated on small samples. The influence of the metal contacts was studied in detail. We also covered large a-Si thin-film transistor (TFT)-plates with PbO. Imaging results from a large detector with an active area of 18 cm /spl times/ 20 cm are presented. The detector has 960 /spl times/ 1080 pixels with a pixel pitch of 184 /spl mu/m. The modulation transfer function at the Nyquist frequency of 2.72 linepairs/mm is 50%. Finally, a full size X-ray image is presented.

PbO as direct conversion X-ray detector material

A flat X-ray detector with lead oxide (PbO) as direct conversion material has been developed. The material lead oxide, which has a very high X-ray absorption, was analysed in detail including Raman spectroscopy and electron microscopy. X-ray performance data such as dark current, charge yield and temporal behaviour were evaluated on small functional samples. A process to cover a-Si TFT-plates with PbO has been developed. We present imaging results from a large detector with an active area of 18 × 20 cm2. The detector has 1080 × 960 pixels with a pixel pitch of 184 μm. The linearity of detector response was verified. The NPS was determined with a total dark noise as low as 1800 electrons/pixel. The MTF was measured with two different methods: first with the analysis of a square wave phantom and second with a narrow slit. The MTF at the Nyquist frequency of 2.72 lp/mm was 50 %. We calculated first DQE values of our prototype detector plates. Full size images of anatomic and technical phantoms are shown.

Fully operational write‐read‐write and random‐access optical store

A write‐read‐write magneto‐optic memory for random access has been made to work as a feasibility model. The memory is an interim result of the development of a 107–108‐bit memory. Design aspects and function of the memory as well as experimental results are summarized. Operation for more than 300 h and more than 109 read‐write cycles has not given rise to any degradation.

Magnetic and magneto-optical properties of TbFeCoCr layers

Abstract The addition of Cr to RE—TM-based magneto-optical layers is the most common way to gain chemical stability of such alloys. The disadvantage of Cr is its tendency to decreases the TM moments. This was observed by a shift of T comp to higher temperatures proportional to the amount of Cr. T C decreased significantly Cr content. The carrier-to-noise ratio of TbFeCoCr disks was 3–5 dB lower than for TbFeCo disks. The reduced TM moments led to a smaller Kerr rotation for wavelengths within the red and infrared region, resulting in a lower carrier level while the noise level did not change.

Magnetic properties of exchange coupled layers for magneto-optical recording

Abstract The influence of FeCo and GdFe intermediate layers on the exchange coupling between DyFeCo initializing layers and TbFeCo memory layers has been investigated. With increasing intermediate layer thickness the exchange coupling is reduced and the coercivity of the initializing layer is increased. The change in coercivity is most probably due to changes in microstructure of the DyFeCo layer. A disk with a stack of 22 nm TbFeCo, 14 nm GdFe and 53 nm DyFeCo yielded a CNR of 51.4 dB in recording experiments.