Search Results - (Author, Cooperation:S. Wirth)

2018-01-18

American Physical Society (APS)

1098-0121

1095-3795

Physics

Electronic structure and strongly correlated systems

2018-05-22

American Physical Society (APS)

1098-0121

1095-3795

Physics

Electronic structure and strongly correlated systems

2018-04-18

American Physical Society (APS)

1098-0121

1095-3795

Physics

Surface physics, nanoscale physics, low-dimensional systems

2012-04-28

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2011-06-17

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2018-11-10

American Association for the Advancement of Science (AAAS)

2375-2548

Natural Sciences in General

1089-7550

AIP Digital Archive

Physics

A measuring procedure for the determination of the switching behavior of hard magnetic particles is presented. For this end, the remanence vector is determined for increasing fields. In the first part of the presented analysis, the angular dependence of the switching field is calculated, neglecting the switching field distribution. In the second part, the portion of switching particles depending on the strength of the applied field and its orientation with respect to the particle easy axes is determined. This switching portion includes information on the angular dependence of the switching field and the switching field distribution for each particle orientation. The method is demonstrated on a magnetically diluted barium ferrite sample with noninteracting single-domain particles.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The magnetic interactions in arrays of nanometer-scale ferromagnetic iron particles enhanced by direct growth onto thin permalloy films were investigated. The magnetic measurements [Hall magnetometry up to 100 K and variable field MFM (magnetic force microscopy) at room temperature] showed that the magnetization behavior of the permalloy was strongly influenced by the presence of the small (∼13 nm in diameter) particles. The mean values of the particles' switching fields coincided with those for noninteracting particles. The switching field distribution of the iron particles, however, was considerably broadened by their interactions. These results for strongly interacting small particles exemplify the magnetization behavior of ever smaller and more dense magnetic storage media. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The magnetization behavior in arrays of small ferromagnetic iron particles is investigated. Arrays were fabricated by a combination of chemical vapor deposition and scanning tunneling microscopy. This method allows a variety of particle arrays to be grown differing in particle height, diameter, or arrangement. Moreover, the arrays can be grown directly onto different materials such as Au or permalloy. Magnetic measurements were conducted by Hall magnetometery up to 100 K and compared to switching field measurements by means of magnetic force microscopy at room temperature. The magnetization reversal mechanisms were studied from magnetization curves measured for an arbitrary angle cursive-theta of the applied field with respect to the long axis of the particles. By analyzing the reversible rotation, the particles' magnetic core diameter and the shape anisotropy could be determined. A phenomenological model based on thermally activated magnetization reversal was introduced and compared to experimental switching field dependences on temperature as well as on cursive-theta. Thermal effects may govern the magnetization reversal in particles of 10 nm diameter at all temperatures. For 14 nm particles and temperatures below 30 K, curling (for cursive-theta≤30°) and homogeneous reversal modes appear to dominate. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A device structure composed primarily of a film made from colossal magnetoresistive (CMR) material and a permanent magnet (PM) film used for biasing the CMR film is proposed as a sensor for magnetic objects. The PM film provides a magnetic field through the CMR film, which is substantially decreased when a magnetic object approaches the device, as part of the magnetic flux is now diverted through the object. To test the feasibility of this concept, we performed simulations of the magnetic field distribution with a three-dimensional finite boundary program. Our vertical model structure consists of a strip of CMR material covered by a PM strip with magnetic in-plane texture and magnetized along its width. The maximum possible biasing field through the CMR material is mainly controlled by the thickness to width ratio of the PM material and cannot be improved by the use of a soft magnetic cladding. The same effect is observed on the flux reduction by approaching a magnetic object. Preliminary results on an experimental realization of the device are given. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We report on a systematic study of the correlation between the disorder produced by ion irradiation and the magnetoresistance (MR) behavior of two doped manganite films: a highly textured La0.67Sr0.33MnO3 film on a (100) LaAlO3 substrate and a film of La0.67Ca0.33MnO3 on a YSZ substrate with a high degree of large-angle grain boundary disorder. The films were grown via metal organic chemical vapor deposition and exposed to irradiation of 200 keV Ne ions. The temperature and field dependence of the resistivity were measured on the same samples at different levels of damage. For the Sr-doped film, the bulk magnetic properties were observed to degrade faster with cumulative damage than transport. For both films at low temperature, a low-field hysteretic MR was either induced or enhanced by ion damage. These effects are discussed in terms of diffusive transport through "granular" magnetically disordered regions. © 1999 American Institute of Physics.

Electronic Resource

1525-1438

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The management of cervical intra-epithelial neoplasia (CIN) has evolved so that excisional techniques are now preferred over ablative procedures. This is in part due to a 1–3% rate of discovering unsuspected early invasive carcinomas that would not have been detected by ablative management of CIN. A review of our initial experience over 20 months with the loop electrosurgical excision procedure (LEEP) in treating CIN found seven out of 237 patients (3%) to have otherwise unsuspected invasive lesions. The management of three additional patients with suspected early invasive lesions has been facilitated by LEEP. The procedure has been found to produce excellent pathologic specimens and has virtually replaced traditional operative cervical conization in the management of both CIN and early invasive cervical cancer.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A new procedure for investigating the switching behaviour of differently oriented particles in polycrystalline samples is introduced where the particle interaction is taken into account by the mean demagnetizing field. Based on specific remanence measurements the angular and field dependence of the probability of irreversible magnetization reversals (switching) is determined. This includes also the switching field distribution (SFD) of the material. The procedure is applied to a barium ferrite sample compacted from small particles. Due to the interaction the angular dependent switching fields are shifted to lower values compared to those predicted by the Stoner–Wohlfarth model and those measured for a strongly diluted sample, whereas the SFD is changed only slightly. This result as well as measurements of the initial susceptibility confirm single–domain particle behaviour of this material. Starting from our result for the switching probability it is shown that the angular dependence of the switching field can be deduced from angular dependent measurements of remanence coercivity only for samples with a very high degree of grain alignment. The determined probability is confirmed by comparing calculated and measured field dependence of the conventional remanence for the investigated material. © 1995 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The singular point detection (SPD) technique as well as a least-mean-square procedure of fitting trial texture functions to demagnetization curves (DMC) were applied in order to determine the orientation density of the tetragonal axes of the Nd2Fe14B crystallites in sintered Nd-Fe-B magnets with different degrees of grain alignment. Both methods are less complicated than calculating the texture function from x-ray-diffraction data. The orientation densities obtained by both methods agree fairly. Analytically, they can be described as a Gaussian or a sum of cosine-power functions of the angle between the local tetragonal axis and the texture axis. This agreement is a test for the DMC method which can also be used for materials showing much larger anisotropy fields than the maximum available measuring field. The SPD and DMC methods can also be applied to measure the temperature dependence of the anisotropy field HA of the magnetic main phase in noncompletely textured polycrystalline materials. By means of the DMC method additionally the spontaneous polarization Js as well as the anisotropy constants K1 and K2 can be determined. As expected, the values of HA of our sintered Nd-Fe-B samples, measured up to 140 °C, are nearly independent of the degree of texture and are in agreement with those reported in literature. This confirms that SPD as well as DMC can be used to measure intrinsic magnetic properties for materials which can hardly be prepared as single crystals, such as interstitial compounds made by gas–solid reactions.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The diffusion of nitrogen in R2Fe17 intermetallics is investigated by an approach which reconciles the solid-solution and immobilization theories of nitrogen diffusion. It turns out that two-sublattice diffusions may yield sharp concentration profiles but leave the phase structure of the nitride unchanged. Beside the reaction time and a local relaxation time there exists a global relaxation time which governs the smoothing of concentration gradients. Due to the large number of unknown energy parameters involved it is difficult to make quantitative predictions, but in general the diffusion behavior depends on factors such as the use of N2 or NH3 as a nitrogen source. © 1998 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The transport properties of metalorganic chemical vapor deposited films of lanthanum manganite grown on various substrates are investigated. The more disordered films show a magnetoresistance that is both large and relatively temperature independent over a wide temperature range. At low magnetic fields, a linear field dependence is observed and is attributed to spin-polarized intergrain tunneling. In addition, at low fields a hysteretic dependence of resistivity on the magnetic field has been observed. This effect has been attributed to the scattering of spin-polarized carriers at the grain boundary. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Hall crosses were used to measure the magnetic properties of arrays of ferromagnetic, nanometer-scale iron particles. The arrays typically consist of several hundred particles of 9–20 nm in diameter. It is shown that the sensitivity of the measurements can be improved by matching the areas of the Hall cross and the array grown onto it by at least an order of magnitude. We predict that single particles of diameter as small as 10 nm can be measured if grown onto Hall crosses of appropriate size. © 2000 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Electronic Resource

0039-6028

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0042-207X

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Electronic Resource