Rotor Slot Permeance Harmonics under Distorted Air-Gap Flux Waveform for Cage Induction Motors

The air-gap flux waveform for a cage induction machine is not sinusoidal in shape and contains various harmonics, including the phase-belt harmonics, slot magnetomotive force (mmf) harmonics, slot permeance harmonics, and saturation harmonics. The slot mmf and permeance harmonics affect the stray losses considerably. Among the saturation harmonics, the third harmonic is usually the most significant one unless it is suppressed by allowing circulating current to flow. The magnitude and phase angle of the saturation harmonics compared to those of fundamental flux waveform depend on whether teeth or core (back iron) section is more saturated. The various amount of third harmonic air gap flux with different phase angle is intentionally injected into a cage induction motor to examine the effects of distorted flux waveform on rotor slot permeance harmonics. For the same air gap fundamental flux, the waveform which has the higher air gap peak flux also produce higher rotor slot permeance harmonics. The stator core losses, no-load rotor high frequency losses, no-load losses, and stray load losses under distorted air gap flux waveforms are presented and discussed.Center for Electromechanic

Magnetic properties of epitaxial single crystal ultrathin Fe\u3csub\u3e3\u3c/sub\u3eSi films on GaAs (001)

Magnetic properties of Fe3Si films with thickness from 2 to 210 monolayers (ML) epitaxially grown on GaAs (001) were studied using a superconducting quantum interference device and alternating gradient force magnetometers. Growth of these single-crystal intermetallic compound films were carried out in a multichamber molecular beam epitaxy (MBE) system. The samples were covered in situ with Au 50 Å thick to prevent oxidation when the samples were removed from the MBE chamber. All the films are ferromagnetic even for samples as thin as 2 ML. The easy magnetization direction of the films is parallel to the film surface. The magnetic coercivity forces (Hc) of the samples increase as the film thickness decreases to 10 ML, and then decrease when the film thickness decreases further to 2 ML

The Kuiper Belt and Other Debris Disks

We discuss the current knowledge of the Solar system, focusing on bodies in the outer regions, on the information they provide concerning Solar system formation, and on the possible relationships that may exist between our system and the debris disks of other stars. Beyond the domains of the Terrestrial and giant planets, the comets in the Kuiper belt and the Oort cloud preserve some of our most pristine materials. The Kuiper belt, in particular, is a collisional dust source and a scientific bridge to the dusty "debris disks" observed around many nearby main-sequence stars. Study of the Solar system provides a level of detail that we cannot discern in the distant disks while observations of the disks may help to set the Solar system in proper context.Comment: 50 pages, 25 Figures. To appear in conference proceedings book "Astrophysics in the Next Decade

Microstructure and thermal stability of Fe, Ti and Ag implanted Yttria-stabilized zirconia

Yttria-stabilized zirconia (YSZ) was implanted with 15 keV Fe or Ti ions up to a dose of 8×1016 at cm−2. The resulting “dopant” concentrations exceeded the concentrations corresponding to the equilibrium solid solubility of Fe2O3 or TiO2 in YSZ. During oxidation in air at 400° C, the Fe and Ti concentration in the outermost surface layer increased even further until a surface layer was formed of mainly Fe2O3 and TiO2, as shown by XPS and ISS measurements. From the time dependence of the Fe and Ti depth profiles during anneal treatments, diffusion coefficients were calculated. From those values it was estimated that the maximum temperature at which the Fe- and Ti-implanted layers can be operated without changes in the dopant concentration profiles was 700 and 800° C, respectively. The high-dose implanted layer was completely amorphous even after annealing up to 1100° C, as shown by scanning transmission electron microscopy. Preliminary measurements on 50 keV Ag implanted YSZ indicate that in this case the amorphous layer recrystallizes into fine grained cubic YSZ at a temperature of about 1000° C. The average grain diameter was estimated at 20 nm, whereas the original grain size of YSZ before implantation was 400 nm. This result implies that the grain size in the surface of a ceramic material can be decreased by ion beam amorphisation and subsequent recrystallisation at elevated temperatures

Superparamagnetic magnetic force microscopy tips

We report on magnetic force microscopy (MFM) images of a thin-film magnetic recording head taken using batch micromachined silicon tips coated with nanocomposite Fe60 (SiO2)40 and Fe70 (SiO2)30 films. The small Fe grain size (\u3c10 nm) and dilute Fe volume fraction (0.29–0.4) of these granular films produce tip coatings of low remanence and essentially zero coercivity, reduced by the superparamagnetic properties of these films. We have used these tips to obtain MFM images of the write field of the head with high spatial and magnetic-field resolution. In comparison to images taken using commercial Co85Cr15-coated tips, these MFM images show reduced tip memory effects and clearly delineate the gap field from the pole pieces

Thickness dependence of the magnetic and electrical properties of Fe:SiO\u3csub\u3e2\u3c/sub\u3e nanocomposite films

Nanocomposite Fe80 (SiO2)20 films with thickness from 150 to 5000 Å have been prepared by rf magnetron sputtering from a composite target. The crystallites in the Fe80 (SiO2)20 films have a bcc structure with the average size of 46–66 Å which was determined by transmission electron microscopy. As indicated by the thickness dependence of resistivity, the stacking and connectivity of the crystallites depend on the thickness of the films. The magnetic properties also depend on the microstructure which changes with the thickness of the films. The magnetic coercivity of the films increases with the thickness of the film, reaches a maximum, and then decreases. The maximum coercivity of 400 Oe at 300 K and 1200 Oe at 5 K was observed for a film with a thickness of about 700 Å

High coercivity rare earth–cobalt films

Rare earth–cobalt (RCo, R=Sm, Pr) films with thicknesses from 30 to 700 nm have been prepared with and without a Cr underlayer by dc magnetron sputtering from a R2Co7 composite target. The as-deposited SmCo films with a Cr underlayer (SmCo║Cr) have magnetic coercivities of about 500–2800 Oe and the PrCo║Cr films have coercivities of about 100–300 Oe, but after annealing at 500 °C coercivities as high as 31 kOe for SmCo║Cr films and 10 kOe for PrCo║Cr films were observed. The as-deposited PrCo films are composed mostly of an amorphous phase with about 30 vol % of crystallites but after annealing at 500 °C the film is transformed completely to crystallites of about 10 nm diameter as revealed by high-resolution transmission electron microscopy (HRTEM). Nanodiffraction and HRTEM studies show that the crystallites have a closed-packed hexagonal structure. HRTEM study also shows that the annealed SmCo films with a Cr underlayer have grain sizes of about 20 nm and the SmCo films without the Cr underlayer have grain sizes of about 10 nm. The large increase in coercivity for the annealed films is due to the growth of the crystallites

Magnetic properties of epitaxial single crystal ultrathin Fe\u3csub\u3e3\u3c/sub\u3eSi films on GaAs (001)

Magnetic properties of Fe3Si films with thickness from 2 to 210 monolayers (ML) epitaxially grown on GaAs (001) were studied using a superconducting quantum interference device and alternating gradient force magnetometers. Growth of these single-crystal intermetallic compound films were carried out in a multichamber molecular beam epitaxy (MBE) system. The samples were covered in situ with Au 50 Å thick to prevent oxidation when the samples were removed from the MBE chamber. All the films are ferromagnetic even for samples as thin as 2 ML. The easy magnetization direction of the films is parallel to the film surface. The magnetic coercivity forces (Hc) of the samples increase as the film thickness decreases to 10 ML, and then decrease when the film thickness decreases further to 2 ML