M(H) shape reconstruction using magnetic spectroscopy

Knowledge about the magnetization behavior M(H) is crucial for the use of magnetic materials in engineering applications. To date many systems exist that are able to measure the magnetization behavior, e.g. VSM, VCM, MOKE. In addition to their huge costs, complex and space-consuming measurement setup, large amount of preparatory work and restricted surface measurements are handicaps which restrict their field of application. Furthermore, the influence of additional physical quantities such as temperature, strain or pressure can only be investigated with great efforts. These influences are, however, of major importance in the development of magnetic sensor systems that are based on the change in magnetic properties.In this paper, a new measurement principle based on a frequency mixing technique is introduced for investigation of the shape of the magnetization curve of soft non-hysteretic magnetic materials. Based on the Taylor expansion of the magnetization curve and the spectral investigation of the inductively detected signal, a mathematical model for the reconstruction of M(H) is proposed. The model is both numerically and experimentally verified. It is shown that the magnetization curve of a nanocrystalline soft magnetic material used in this study can be reconstructed very accurately and the influence of an additional parameter, i.e. strain, can be investigated in detail as well.     

One and Two Photon Excitation of Radiofrequency Trapped Ca

Radiofrequency （rf） trapped ions are versatile candidates for a large panel of applications ranging from quantum information to the creation of cold molecules. Sample size can range from a single to 10^6 ions, and the internal and external energy states of the atoms can be controlled with high precision. In the experiment, we focus on different protocols related to frequency metrology using rf trapped Ca.     

Discrete element study of viscous flow in magnetorheological fluids

Using discrete element simulations, we gain insight into the structure of a magnetorheological fluid (MRF) under shear. In simulations with flat walls, the particles arrange in chains, sheet-like structures, or columns along the magnetic field lines, depending on the strength of the applied external magnetic field. Corresponding to the structure formation, three different types of failure mechanisms can be identified. For the characterization of the different regimes, specific particle coordination numbers are introduced. The three structural regimes can be distinguished and described by means of these coordination numbers. To analyze the contact between the MRF particles and the walls of the shear cell, additional simulations with rough walls have been conducted. The resulting structure formation could be successfully classified by the introduced coordination numbers. Based on the analysis of the shear stress transmission both in the case of flat and rough walls, possibilities for shear stress enhancement for technological applications are discussed.     

Collisions between tunable halo dimers: exploring an elementary four-body process with identical bosons

We study inelastic collisions in a pure, trapped sample of Feshbach molecules made of bosonic cesium atoms in the quantum halo regime. We measure the relaxation rate coefficient for decay to lower-lying molecular states and study the dependence on scattering length and temperature. We identify a pronounced loss minimum with varying scattering length along with a further suppression of loss with decreasing temperature. Our observations provide insight into the physics of a few-body quantum system that consists of four identical bosons at large values of the two-body scattering length.     

Recoil momentum spectroscopy of highly charged ion collisions on magneto-optically trapped Na

We have used a cold ( T<1 mK), laser-cooled target of Na atoms confined in a magneto-optical trap to study electron capture processes during highly charged ion-sodium atom collisions at keV energies. Momentum distributions of target ions were determined by employing time-of-flight and position sensitive detection of the Na ions, produced during the collisions and extracted by a weak electric field. In this way impact parameter sensitive information about multielectron capture processes is obtained.     

Steric and electronic effects in cyclic alkoxyamines--synthesis and applications as regulators for controlled/living radical polymerization

The synthesis of new six- and seven-membered cyclic alkoxyamines bearing ethyl groups at the alpha-N position of the alkoxyamines is described. The key step in the synthesis of the sterically hindered six-membered cyclic alkoxyamines is a Wadsworth-Horner-Emmons olefination with bisphosphonate 1. The seven-membered cyclic alkoxyamines were prepared from the corresponding six-membered keto alkoxyamines by ring-enlargement with trimethylsilyl(TMS)-diazomethane. The use of the new alkoxyamines as regulators/initiators for radical polymerization is discussed. Efficient controlled and living polymerization of styrene and n-butyl acrylate was obtained with the six-membered tetraethyl alkoxyamine 13. Controlled polymerizations can be conducted even at 90 degrees C. In addition, alkoxyamine 13 can be used for the preparation of AB diblock and ABA triblock copolymers with narrow polydispersities. The influence of the replacement of methyl groups in the alpha-position of the N atom in cyclic alkoxyamines by larger ethyl groups on the styrene polymerization (reaction time, PDI, kinetics of the C-O bond homolysis) is discussed. In addition, thermal decomposition of the new alkoxyamines was studied. Furthermore, the synthesis of N,N-bissilylated alkoxyamines is described. The silylated alkoxyamines are not suitable as regulators/initiators for the controlled/living radical polymerization. The C-O bonds in silylated alkoxyamines are stronger than the C-O bonds in analogous N,N-dialkylated alkoxyamines. The experimental results are verified by calculations with Gaussian 98 (A. 9).