The quasi-static magnetization curve of the magnetic Ba-ferrite (BaFe12O19) glass ceramics is analyzed. This recently presented material is isotropic with a high coercivity Hc. From its structural peculiarities, the magnetic properties are explained as an assembly property of mutually separated, disk-shaped, uniaxial, single-domain particles. An extension of the classical Stoner–Wohlfarth theory is derived where a relatively weak dipolar interaction appears as an effective stochastic magnetic field which becomes, for large volume packing fractions η of the magnetic particles, strongly dependent on the particle orientation and details of the short-range order. Three parameters are sufficient to characterize the structural details of the assembly: η, the mean aspect ratio 〈d〉 of the particles, and a new one describing the short-range order. An analytic approximant of the theoretical magnetization curve for η=0.64 is outlined. Both the shape anisotropy of the particles and the fluctuating part of the effective stochastic magnetic field diminish the theoretical Hc compared with the Stoner–Wohlfarth value. The stable branch of the experimental magnetization curve (first quadrant) of a dense glass ceramic (η≈0.6) is well fitted by the theory thus allowing the determination of structural parameters. There remain significant deviations between the (fitted) theoretical and experimental magnetization curve near Hc. In particular, the experimental Hc is smaller than the predicted one. This is explained by an unsuitable particle size distribution with a significant contribution of large particles which turn into a multi-domain behavior approaching Hc.

LaSr-manganate (LaSr)MnO3 with perovskite structure was prepared in the basic system MnO2–SrO–La2O3–B2O3(–SiO2) by a modified glass crystallization method. X-ray diffraction, magnetic measurements, EDX and particle size investigations (specific surface) were carried out. The influence of the annealing conditions on the phase composition and the magnetic properties of the powders are discussed. In the silicate-free system manganate powder samples show values of specific saturation magnetization up to 53 Am2/kg, a Curie temperature between 369 and 389 K and a mean particle size in the order of 100 nm. The powders reveal the magneto-resistive effect. In the silicate system the borate phase was leached out to get a manganate-SiO2 mixture which could be sintered to bulk samples. The sintering conditions have been varied to avoid a decrease of the magnetization due to the formation of non-magnetic phases. Sintered samples show a superposition of the CMR and the GMR effect due to grain boundaries.

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(LaSr)MnO3 powders with perovskite structure were prepared in the basic system MnO2–SrO–La2O3–B2O3 for the first time by a modified glass crystallization method. The annealing temperature was changed between 600 and 950°C. X-ray diffraction, magnetic measurements, ESMA and particle size investigations (specific surface) were carried out. The influence of the annealing conditions on the phase composition, the cation contents and the magnetic properties of the powders is discussed. Powder samples prepared under optimized conditions show values of specific saturation magnetization between 48 and 53Am2/kg, a Curie temperature between 369 and 389K and specific surfaces of about 10m2/g corresponding to a mean particle size of 100nm. The powders reveal the magneto-resistive effect.

For direct writing of electrically conducting connections and areas into insulating gold oxide thin films a scanning Ar+ laser beam and a 30 keV Ga+ focused ion beam (FIB) have been used. The gold oxide films are prepared by magnetron sputtering under argon/oxygen plasma. The patterning of larger areas (dimension 10–100 μm) has been carried out with the laser beam by local heating of the selected area above the decomposition temperature of AuOx (130–150 °C). For smaller dimensions (100 nm to 10 μm) the FIB irradiation could be used. With both complementary methods a reduction of the sheet resistance by 6–7 orders of magnitude has been achieved in the irradiated regions (e.g. with FIB irradiation from 1.5×107 Ω/□ to approximately 6 Ω/□). The energy-dispersive X-ray analysis (EDX) show a considerably reduced oxygen content in the irradiated areas, and scanning electron microscopy (SEM), as well as atomic force microscopy (AFM) investigations, indicate that the FIB patterning in the low-dose region (1014 Ga+/cm2) is combined with a volume reduction, which is caused by oxygen escape rather than by sputtering.

Doped La-manganites belong to the class of perovskite materials showing the so-called colossal magnetoresistance effect (CMR) near their Curie temperature Tc, which can be varied in a wide range up to 380K. The magnetoresistance (MR) ratio of sputtered epitaxial films changes strongly with their Tc from 8000% at 90K to 35% at 310K in a field of 1T. Bicrystalline and polycrystalline films show an additional MR effect below Tc. Whereas the CMR effect is caused by a magnetic phase transition the low-temperature MR effects are induced by the transport of spin-polarized carriers across grain boundaries acting as tunneling barriers. The CMR effect is interesting for applications especially in position sensors because of its large dynamic range without hysteresis and saturation effects.

High-T/sub c/ GdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(GBCO) superconducting transition edge bolometers with operating temperatures near 90 K have been made with both closed silicon-nitride membranes and patterned silicon-nitride (SiN) spiderweb-like suspension structures. As a substrate silicon-on-nitride (SON) wafers are used which are made by fusion bonding of a silicon wafer to a silicon wafer with a silicon-nitride top layer. The resulting monocrystalline silicon top layer on the silicon-nitride membranes enables the epitaxial growth of GBCO. By patterning the silicon-nitride the thermal conductance G is reduced from about 20 to 3 /spl mu/W/K. The noise of both types of bolometers is dominated by the intrinsic noise from phonon fluctuations in the thermal conductance G. The optical efficiency in the far infrared is about 75% due to a goldblack absorption layer. The noise equivalent power NEP for FIR detection is 1.8 pW//spl radic/Hz, and the detectivity D* is 5.4/spl times/10/sup 10/ cm /spl radic/Hz/W. Time constants are 0.1 and 0.6 s, for the closed membrane and the spiderweb like bolometers respectively. The effective time constant can be reduced with about a factor 3 by using voltage bias. Further reduction necessarily results in an increase of the NEP due to the 1/f noise of the superconductor.

A novel Ba-ferrite powder preparation technique is presented where the magnetic particles become well separated from each other up to at least 70 mass% Ba-ferrite content. Starting from this, a compact glass ceramics can be fabricated where the separation of the Ba-ferrite crystallites is maintained. The magnetic properties of both the powder and the glass ceramics are well described by a modified Stoner—Wohlfarth behaviour.

Magnetic properties of magnetic ceramics are dependent on the magnetisation processes. They are usually dominated by Bloch-wall displacements in multi-domain structures of the sintered magnetic material, even if the starting powder material shows single-domain Stoner–Wohlfarth behaviour. Domain wall motion limits in several cases the quality of magnetic materials for special applications like permanent magnets or rf devices. We have developed a new type of magnetic powder preparation which permits the fabrication of compact glass ceramics containing Ba-ferrite maintaining the single-domain behaviour of the starting powder. This technology is based on the glass crystallisation method for the precipitation of single-domain Ba-ferrite particles in a quenched melt of Fe2O3–BaO–B2O3(-SiO2). By milling the crystallized melt or leaching out the borate from the SiO2-containing glass, a glass ceramic powder containing Ba-ferrite can be produced, which can be sintered at moderate temperatures providing a dense compact glass ceramic containing up to 90wt% Ba-ferrite. This compact glass ceramic shows the same single-domain behaviour as the starting powders, i.e. it also possesses the high coercivities of hard magnetic material.

An experimental study regarding the noise properties of thin superconducting films of composition GdBa2Cu3O7−x on silicon membranes is reported. Noise measurements that include a determination of the Hooge parameter αH as a function of resistance have been carried out at temperatures 78 K200 K most likely is assigned to an increasing interaction and charge fluctuations between the metallic overlayer and the semiconducting silicon membrane material beneath. The magnetron sputtered epitaxial GdBa2Cu3O7−x films consistently revealed Hooge parameters αH <0.04 near the transition temperature, representing the smallest values ever reported for high Tc-films on silicon substrates. Based on these data, the achievable bolometric detectivity D* of superconducting transition edge microbolometers has been calculated. The model calculations fully confirm recent experimental data obtained for various degrees of thermal isolation.

Epitaxial ferromagnetic La0.8Sr0.2MnO3−δ films have been sputtered on SrTiO3 bicrystal substrates. Etched patterns crossing the bicrystal grain boundary are compared with identical patterns not crossing it. The films were annealed at different conditions and their magnetoresistance measured as a function of temperature T and of in plane magnetic field H strength and direction. Annealing at 900 °C was found to modify the grain boundary and to increase its magnetoresistance. For H=±80 Oe parallel to the grain boundary and T=32 K narrow magnetoresistance peaks of 60% height are measured. They are interpreted in the frame of an in plane magnetotunneling structure.

The paper presents a detailed discussion of the current-voltage characteristic of intrinsic Josephson junctions in Bi2Sr2CaCu2O8+delta and Tl2Ba2Ca2Cu3O10+delta. In these materials Josephson tunnel junctions are formed naturally between adjacent superconducting CuO2 bilayers or trilayers. A typical sample consists of a stack of Josephson junctions. We explicitly show that all junctions inside a given sample have identical tunneling characteristics. We discuss the shape (general curvature) of the current-voltage characteristic in terms of a superconducting order parameter that has a predominant d(x2-y2) symmetry. The IcRn product of the intrinsic Josephson junctions turns out to be 2-3 mV, about 10% of the maximum energy gap Delta(0)/e. The current-voltage characteristic of every individual junction exhibits pronounced structures in the subgap regime. They are best explained by a recently proposed resonant coupling mechanism between infrared active optical c-axis phonons and oscillating Josephson currents.

In this paper we describe the design, fabrication and performance of a high-T/sub c/ GdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superconductor bolometer positioned on a 2/spl times/2 mm/sup 2/, 1 /spl mu/m thick silicon nitride membrane. The bolometer structure has an effective area of 0.64 mm/sup 2/ and was grown on a specially developed silicon-on-nitride layer. This layer was made by direct bonding of silicon nitride to silicon after chemical mechanical polishing. The operation temperature of the bolometer is 85 K. A thermal conductance G=3.3/spl middot/10/sup -5/ W/K with a time constant of 27 ms has been achieved. The electrical noise equivalent power (NEP) at 5 Hz is 3.7/spl middot/10/sup -12/ WHz/sup - 1/2 / which is very close to the theoretical phonon noise limit of 3.6/spl middot/10/sup -12/ WHz/sup - 1/2 /, meaning that the excess noise of the superconducting film is very low. This bolometer is comparable to other bolometers with respect to high electrical performance. Our investigations are now aimed at decreasing the NEP for 84 /spl mu/m radiation by further reduction of G and adding an absorption layer to the detector. This bolometer is intended to be used as a detector in a Fabry-Perot based satellite instrument, designed for remote sensing of atmospheric OH.

Experimental results of noise properties of high temperature superconducting GdBaCuO films on thin Si membranes with YSZ buffer layer are reported. Noise measurements have been carried out within 80-300 K temperature range and 2 Hz - 10 kHz frequency range. Four characteristic zones with different temperature dependences of noise voltage have been revealed. The films have the smallest Hooge parameter alpha(H) = 0.04 of those published for high-temperature superconducting films on Si substrates. The low 1/fnoise level allowed to observe phonon noise in the middle of transition. A special attention has been paid to the investigation of noise degradation of films.

Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ (TBCCO) thin films have been deposited on top of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films. Both layers are superconducting with T/sub c/ values of 105 K and 75 K respectively and in superconducting contact. XRD scans show the TBCCO film to grow epitaxially and c-axis oriented on the YBCO ground layer. Possible applications for such multilayers are novel concepts for intrinsic Josephson arrays requiring well defined mesa structures of TBCCO.

Epitaxial ferromagnetic manganite films have been sputtered on bicrystal substrates. Their magnetoresistance was measured as a function of magnetic field and temperature. The grain boundary magnetoresistance at low temperature is separated from the intrinsic magnetoresistance near the Curie temperature. The grain boundary magnetoresistance peaks at about 100 Oe and saturates at about 2 kOe. For a La0.8Sr0.2MnO3 film with a grain boundary angle θ=36.8° a field independent component r0=4.1×10−6 Ω cm2 was separated from a field-dependent component which has its maximum rH=2.3×10−6 Ω cm2 for H of order the coercive field.

A high-T-c GdBa2Cu3O7-delta superconducting transition edge bolometer built on a 1 mu m thick silicon nitride membrane was fabricated and characterized. A thin monocrystalline Si layer on tap of a SixNy membrane (Silicon-On-Nitride SON) was used as the starting substrate. This SON structure was made by direct wafer bonding after Chemical Mechanical Polishing (CMP). Between the Si layer and the HTS film a YSZ/CeO2 buffer layer is used. To prevent degradation the HTS dim is covered by a layer of PtOx. A thermal conductance of G=3.3.10(-5) W/K with a time constant of 27 ms has been achieved using a 2x2 mm(2) membrane. The electrical Noise Equivalent Power (NEP) at 5 Hz is 3.7.10(-12) W/Hz(1/2) which is very close to the theoretical phonon noise limit of 3.6.10(-12) W/Hz(1/2), indicating that the excess noise of the superconducting film is very low. This value corresponds with an electrical detectivity D* of 2.2.10(10) cmHz(1/2)/W, which is unequaled by other reported HTS bolometers. Our investigations are now aimed at decreasing the NEP for 84 mu m radiation by adding an absorption layer and by further reduction of G. This bolometer is intended to be used as a detector in a Fabry-Perot based satellite instrument, designed for remote sensing of atmospheric OH.

For the visible spectral range different types of sensitive radiation detectors are available especially high sensitive and fast quantum detectors based on semiconducting materials. However, for the IR range there is a lack of detectors, especially for the FIR range between 10 µm and 1000 εm wavelength. This wavelength region is of actual importance for spectroscopic purposes as well as for communication systems. For spectroscopic investigations two competing techniques are under developement, the optical and the rf-technique.