Analysis of Magnetization Reversal Process of Nd-Fe-B Sintered Magnets by Magnetic Domain Observation Using Kerr Microscope

We used a Kerr microscope, image processing, and photo editing to clarify magnetization reversal and its propagation in a sintered Nd-Fe-B magnet. Magnetic domain change was observed when a dc field from +20 to 20 kOe was applied to a sintered Nd-Fe-B magnet. Simultaneous magnetization reversal in several grains along the easy axis direction and its propagation to neighboring grains occurred. This indicates that the nucleation field in a grain and magnetic interaction between grains are important controlling factors of the coercivity of sintered Nd-Fe-B magnets

Domain Wall Pinning by Step-Like Thickness Change in Magnetic Thin Film

A thin-film element with a steplike thickness change has been fabricated to investigate experimentally a pinning effect of domain walls by a shape control of thin-film devices. Using a Kerr microscope, domain observation has been done to measure pinning characteristics of the element. It has been shown that 40% steplike thickness change of the film thickness can realize a wall pinning, and a pinning field of 2.53 Oe is obtained. The pinning field increases with increasing steplike thickness change ratio

Analysis of the Demagnetization Process of Nd-Fe-B Sintered Magnets at Elevated Temperatures by Magnetic Domain Observation Using a Kerr Microscope

Magnetization reversal and its propagation in sintered Nd–Fe–B magnets were clearly observed at elevated temperatures up to 150 °C using a Kerr microscope, image processing, and photo editing. Simultaneous magnetization reversal in several grains along the easy axis direction occurred at elevated temperature, and the extent of simultaneous magnetization reversal increased with temperature. This indicates that reduction in the coercivity of Nd–Fe–B sintered magnets at elevated temperatures is attributable to decrease in anisotropy and insufficient pinning of domain walls at grain boundaries

Miniaturization of High-Frequency Carrier-Type Thin-Film Magnetic Field Sensor Using Laminated Film

We examined a laminated high-frequency carrier-type thin-film magnetic field sensor that consists of CoNbZr soft magnetic films with Nb nonmagnetic conductive interlayer. The lamination can change domain structure of the sensor and obtain high sensitivity. An impedance change of 6 /spl Omega/ and a gain of 43 k/spl Omega//T was achieved when the length of the laminated sensor was 1 mm. The gain is four times larger than that of a monolayer sensor

Relationship Between Output of a Fluxgate Sensor and Magnetization Process of Its Core

Motivated by the need to miniaturize fluxgate sensors, we investigated the dependence of the sensitivity of fluxgate sensors on the saturation flux density and magnetostriction of an amorphous ribbon core. In addition, the relationship between the sensing properties and the magnetization process of its core was investigated with a Kerr microscope. We found that the sensitivity decreased with an increase in magnetostriction. Highly magnetostrictive amorphous ribbons exhibited maze domains that were difficult to move by applying a low magnetic field of a few hundred amperes per meter. This effect caused a decrease in the sensitivity of the sensors

Magnetic domain observation of hydrogenation disproportionation desorption recombination processed Nd－Fe－B powder with a high-resolution Kerr microscope using ultraviolet light

A Kerr microscope that uses ultraviolet (UV) light for high-resolution domain observation was built, and the domain structure and magnetization process of hydrogenation disproportionation desorption recombination (HDDR) powder were examined. The UV Kerr microscope could observe nanometer-sized domain patterns. Applying a dc field of 1.0 kOe to HDDR powder at a desorption recombination (DR) time of 12 min produced abrupt wall motion. The pinning force exerted by the grain boundaries is inadequate for producing high coercivity because the Nd-rich phase layers along these boundaries are absent at a DR time of 12 min. For HDDR powder at a DR time greater than 14 min, changing the magnetic field by up to 1.0 kOe produced no observable wall motion. It follows that the high coercivity of HDDR powder is due to domain wall pinning at the grain boundaries

Renal pericytes: regulators of medullary blood flow

Regulation of medullary blood flow (MBF) is essential in maintaining normal kidney function. Blood flow to the medulla is supplied by the descending vasa recta (DVR), which arise from the efferent arterioles of juxtamedullary glomeruli. DVR are composed of a continuous endothelium, intercalated with smooth muscle-like cells called pericytes. Pericytes have been shown to alter the diameter of isolated and in situ DVR in response to vasoactive stimuli that are transmitted via a network of autocrine and paracrine signalling pathways. Vasoactive stimuli can be released by neighbouring tubular epithelial, endothelial, red blood cells and neuronal cells in response to changes in NaCl transport and oxygen tension. The experimentally described sensitivity of pericytes to these stimuli strongly suggests their leading role in the phenomenon of MBF autoregulation. Because the debate on autoregulation of MBF fervently continues, we discuss the evidence favouring a physiological role for pericytes in the regulation of MBF and describe their potential role in tubulo-vascular cross-talk in this region of the kidney. Our review also considers current methods used to explore pericyte activity and function in the renal medulla

London equation studies of thin-film superconductors with a triangular antidot lattice

We report on a study of vortex pinning in nanoscale antidot defect arrays in the context of the London Theory. Using a wire network model, we discretize the array with a fine mesh, thereby providing a detailed treatment of pinning phenomena. The use of a fine grid has enabled us to examine both circular and elongated defects, patterned in the form of a rhombus. The latter display pinning characteristics superior to circular defects constructed with the similar area. We calculate pinning potentials for defects containing zero and single quanta, and we obtain a pinning phase diagram for the second matching field, $H = 2 \Phi_{o}$.Comment: 10 pages and 14 figure