J. Pelzl

Gilbert damping and g-factor in FexCo1−x alloy films

Abstract The Gilbert damping parameter, G, determined from ferromagnetic resonance (9 – 92 GHz), is presented as a function of concentration, x, for single crystalline FexCo1−x alloy films prepared by rf sputtering. On the Fe-rich side, a plateau-like behavior is found for G(x), extending to about x = 0.5. In addition, the g-factor, g, is shown to exhibit a very similar dependence, in agreement with theoretical calculations which relate these two quantities via the spin-orbit coupling. It is seen that the compositional dependence of both G(x) and g(x) cannot be described by a simple interpolation between the values for the pure elements.

Spin–orbit-coupling effects on g-value and damping factor of the ferromagnetic resonance in Co and Fe films

The spectroscopic splitting factor g and the Gilbert damping constant G are magnetic parameters accessible to ferromagnetic resonance (FMR) measurements, which apart from the magneto-crystalline anisotropy energy can provide information on the spin–orbit coupling in magnetically ordered material. Whereas the effect of spin–orbit coupling has been thoroughly investigated and is well understood in insulating transition metal compounds, in 3d-metallic magnetic compounds the microscopic mechanism still needs further clarification. Particularly in thin films and multilayers interface effects and interaction between layers can modify both spin and orbital moments leading to changes of the g-value and the Gilbert damping constant. Experimental results are presented from frequency dependent FMR measurements on Co epitaxial films grown on Cr(001) and on films of the alloy Co1−xFex(100) deposited on MgO(001), and from recent studies on Fe(100) films grown on InAs(001). The experimental data yield clear evidence of the importance of surfaces or interfaces of the films on the magnitude of orbital and spin moment.

Stray-light correction in photoacoustic measurements of solid samples

An experimental correction procedure is presented which allows one to measure separately and to eliminate signal contributions produced at the walls of photoacoustic cells by the directly incident light or by the light (diffusively) reflected from the solid sample. This stray‐light correction procedure is tested for an opaque and a transparent photoacoustic cell. It helps to reduce the systematic error of photoacoustic measurements considerably when the solid to be analyzed and the reference material have different reflection properties and when in quantitative thermal depth profiling a larger interval for the modulation frequency of heating is needed.

Conventional and photothermally modulated ferromagnetic resonance investigations of anisotropy fields in an epitaxial Fe(001) film

Conventional angle‐dependent ferromagnetic resonance (FMR) measurements on an epitaxial (001) Fe film grown on a GaAs substrate were performed as a function of the orientation of the external magnetic field Bext for three configurations: One with Bext in the film plane and two with Bext out of plane starting in plane in different crystallographic orientations. From these measurements the magnetization M, the crystalline anisotropy constants K1 and K2, the surface anisotropy Ks and an additional uniaxial anisotropy Ku were deduced self‐consistently. The temperature dependence of K1 and M was investigated for the in‐plane [110] orientation in the range from 100 to 570 K. In addition, locally resolved photothermally modulated FMR measurements were carried out to study the homogeneity of the magnetization and of the crystalline anisotropy across the film. Disturbances of both magnetic parameters as a function of position were observed which are related to local inhomogeneities in the semiconducting substrate.

Extremum method: Inverse solution of the two-layer thermal wave problem

An inverse solution of the two-layer thermal wave problem has been derived, which allows us to determine the relevant thermal transport parameters, the thermal diffusion time and the thermal reflection coefficient, respectively, the ratio of the effusivities of the two layers, deduced from the relative minimum or maximum of the calibrated phase lags measured between the periodically modulated excitation of the thermal wave and the detected thermal response. Applying a functional transformation by multiplying the calibrated phase lags with the variable (1∕f1∕2)q, where f is the modulation frequency of excitation and q a positive or negative real number close to zero, the inversion method is extended to other values of the calibrated phase lags measured in the neighborhood of the phase minimum or maximum. The application potential of these two solution methods is studied by analyzing the phase lags measured as a function of frequency for two-layer systems of technological importance, e.g., different plasma-...

A linear relationship between the Hall carrier concentration and the effective absorption coefficient measured by means of photothermal radiometry in IR semi-transparent n-type CdMgSe mixed crystals

In this work we demonstrate the ability to measure the effective infrared absorption coefficient in semiconductors by a photothermal infrared radiometry (PTR) experiment, and its correlation with the Hall carrier concentration. The amplitude and phase of the PTR signal were measured for Cd1?xMgxSe mixed crystals, with the magnesium content varying from x = 0 to x = 0.15. The PTR experiments were performed at room temperature in thermal reflection and transmission configurations using a mercury cadmium telluride infrared detector. The PTR data were analyzed in the frame of the one-dimensional heat transport model for infrared semi-transparent crystals. Based on the variation of the normalized PTR phase and amplitude on the modulation frequency, the thermal diffusivity and the effective infrared absorption coefficient were obtained by fitting the theoretical expression to experimental data and compared with the Hall carrier concentration determined by supplementary Hall experiments. A linear relationship between the effective infrared absorption coefficient and the Hall carrier concentration was found which is explained in the frame of the Drude theory. The uncertainty of the measured slope was 6%. The value of the slope depends on (1) the sample IR absorption spectrum and (2) the spectral range of the infrared detector. It has to be pointed out that this method is suitable for use in an industrial environment for a fast and contactless carrier concentration measurement. This method can be used for the characterization of other semiconductors after a calibration procedure is carried out. In addition, the PTR technique yields information on the thermal properties in the same experiment.

Spectroscopic investigation of [(NH4)xK1−x]2SnCl6 mixed crystals

Abstract Polycrystalline samples of the solid solution [(NH4)xK1−x]2SnCl6(0⩽x⩽ 1) have been investigated by DSC, X-ray diffraction and Raman scattering experiments. Substitution of K+ by NH+4 depresses the phase transition temperature T1. For 0⩽ x ⩽0.05 a linear temperature coefficient d T 1 dx=−5.16 K/mol % is obtained. The cubic lattice constant roughly obeys Vegards law, whereas the linewidth of the SnCl62−F2g internal vibration displays a nonlinear dependence on composition.

Study of the hot spot of an in-plane gate transistor by scanning Joule expansion microscopy

The local heat dissipation of an in-plane gate (IPG) transistor was investigated by means of a thermally modulated scanning Joule expansion microscope. The nanostructured sample was prepared by focused ion beam techniques. The temperature induced thermal expansion and the topographic information are measured simultaneously. The spatial resolution of the constructed microscope is below 50 nm. Heat spots of the semiconducting devices are visualized by heating them with modulated drain voltage. The heat spot position and the temperature amplitude of the heat spot on the IPG transistor depend on the gate voltage VG. With an increasing negative magnitude of VG the heat spot displaces in the direction from drain towards source. Simultaneously the temperature amplitude of the maximum of the heat spot and the thermal expansion integrated over the heated area decrease linearly.

Use of electron spin resonance for the determination of staling of roast coffee in polyethylene bag packs

ZusammenfassungKaffeebohnen der SorteArabica wurden unmittelbar nach der Röstung in Beuteln aus Polyäthylen verpackt. In Abständen von 30 Tagen wurde jeweils eine Packung geöffnet und der Säuregrad und die Elektronenspinresonanz (ESR) der Kaffeebohnen untersucht. Die ESR-Messungen wurden an den gleichen Proben nach 30 Tagen offener Lagerung wiederholt. Außerdem wurde in regelmäßigen Intervallen der Säuregrad von Bohnen aus der zuerst geöffneten Packung bestimmt. ESR-Untersuchungen erfolgten auch an gemahlenen Kaffeebohnen, die in verschieden großen offenen Behältern gelagert wurden. Bei allen Proben wird eine Abnahme der ESR-Signalintensität mit der Zeit beobachtet, die mit einer Zunahme des Säuregrades verbunden ist. Die Änderungsrate hängt sowohl von der Vorbehandlung der Proben, als auch von der Lagerungsdauer ab. Auf der Basis der ESR-Ergebnisse wird eine Alterungsgeschwindigkeit definiert, die es erlaubt, den Alterungsprozeß des gerösteten Kaffees zu quantifizieren.SummaryArabica roasted beans packed in polyethylene bags were investigated at intervals by chemical analysis (acidity index) and by electron spin resonance (ESR) over a period of 30 days. The ESR measurements were repeated on the same samples after being exposed to air over a period of 30 days. Simultaneously, the acidity index of beans in an open bag was determined at regular intervals. ESR studies were also performed on ground beans, which were maintained in contact with air in two different containers. For all samples, the ESR intensity decreased as a function of time, whereas the acidity index increased simultaneously. The rate of change depended upon the treatment of the sample as well as on the storage time in the bag. On the basis of the ESR results an ageing velocity is defined, which allows for the quantification of the staling of roast coffee.

Thermal wave imaging by photothermally modulated ferromagnetic resonance

Thermal wave modulated ferromagnetic resonance has been used to investigate local magnetic properties of ferromagnetic materials. The sample inside the microwave cavity is exposed to a modulated laser beam and the reflected microwave power is measured as a function of beam position and modulation frequency. First results are obtained from magnetic recording tapes.