Demagnetization

A new software package called CryoMag to carry out measurements of magnetic moments is presented. It is designed to work with SQUID magnetometers manufactured by 2G Enterprises, but the modular design allows easy adaption to other instruments like spinner magnetometers as well. The measurement process is optimized for, but not limited to, stepwise demagnetization experiments commonly used in paleomagnetism. A graphical representation of the data is always visible to the user in the form of orthogonal, stereographic and decay plots, which can be represented in in-situ, geographic or tilt corrected coordinates and can be saved to graphics files. Measurement positions can be easily customized. A comprehensive record of detailed measurement and statistical data is stored in XML (eXtensible Markup Language) based data files (*.cmag.xml). The final results of the measurements can be exported to various common file formats for further processing. The software is written in Python, an open source, cross-platform programming language and can therefore be used on all major operating systems like Windows, Linux and MacOS X (not tested).

Martian crust endured several large meteoroid impacts subsequent to the demise of an early global magnetic field. Shock pressures associated with these impacts demagnetized parts of the crust, to an extent determined by shock resistance of magnetic materials in the crust. Impacts that form large basins generate pressures in excess of 1 GPa within a few crater radii of their impact sites. Crustal materials near the surface experience significantly reduced impact pressure, which varies with depth and distance from the impact point. We present new demagnetization experiments on magnetite (Fe3O4), hematite (alpha-Fe2O3), and titanohematite (Fe2-xTixO3 where x < 0.2). Our measurements show that pressures of similar to 1 GPa are sufficient to partially demagnetize all of these minerals. The efficiency of demagnetization by impact pressure is proportional to the logarithm of the minerals' magnetic coercivity. The impact pressure magnetic response from exsolved titanohematite samples is consistent with the magnetization decay near Prometheus impact basin and may point to an oxidized igneous rock in Terra Sirenum region at the time of acquisition of magnetic remanence. The remaining magnetic anomalies near large impact basins suggest moderate crustal coercivity. These anomalies point to titanomagnetite as a magnetic carrier and more reduced condition during crustal formation.

In this paper, we analyzed and compared changes of demagnetization under fault conditions and commutation torque ripples in a PM BLDC motor. Changes of freewheeling current are analyzed at different speeds. Commutation torque ripple is analyzed in the freewheeling current section. Also, the change of demagnetization phenomenon is compared and analyzed through a change of flux density according to the change of freewheeling current. Consequentially, we studied reliability and stability through changes of demagnetization and commutation torque ripple.

The majority of the work performed for detecting eccentricity faults for permanent magnet synchronous motors (PMSM) focus on motor current signature analysis (MCSA), as it provides continuous on-line monitoring with existing current sensors. However, MCSA cannot be applied under nonstationary conditions and cannot distinguish faults with load torque oscillations, which are limitations for many PMSM drive applications. In this paper, it is shown that the d-axis inductance, Ld, decreases with increase in the severity of eccentricity due to the change in the degree of magnetic saturation, and it is proposed as a new fault indicator. The inverter can be used to perform a standstill test automatically whenever the motor is stopped, to measure Ld for eccentricity testing independent of load variations or oscillations, which is not possible with MCSA. An FE and experimental study on a 10hp PMSM verifies that eccentricity can be detected independent of the load with high sensitivity and reliability.

The effects of magnet faults on the rotor of permanent magnet synchronous machines are analyzed in the present work. In particular, demagnetization effects are analyzed using the finite element method. Two different stator winding configurations are considered in the analysis, series and parallel connected windings. From this analysis, a fault detection strategy based on the information contained in winding-current spectrum is proposed. A fault severity factor is also proposed to quantify residual magnetism losses (demagnetization) on a single magnet. This factor is practically independent from the motor load conditions. Experimental results are presented to validate the proposal.

We report the temperature dependence of in-phase and quadrature susceptibilities, k&#x27; and k&quot;, between 20 K and 300 K for a stoichiometric natural single crystal of magnetite. Measurements were made for amplitudes of the AC driving field ranging from H = 30 A/m to 2 kA/m and frequencies ranging from f = 40 Hz to 4 kHz. In cubic magnetite above the Verwey transition, Tv = 120 K, k&#x27; is limited by self-demagnetization and does not vary greatly with T, H or . As the crystal cools through Tv and transforms to monoclinic structure, k&#x27; decreases by about a factor 2, with a further more gradual decrease of 10-20% in cooling from 40 to 20 K. Saturation remanence also drops sharply at Tv but shows no further change in cooling below 40 K. Thus it appears that domain walls remain pinned throughout the 20-40 K range but small segments undergo reversible oscillations in an AC field, the amplitude of oscillation decreasing steadily with cooling below 40 K. In this same range, k&q...

The magnetic field signatures of large demagnetized impact basins on Mars offer a unique opportunity to study the magnetic properties of the crust and the processes of basin formation and impact shock demagnetization. We present a framework for determining the effects on such signatures due to the dominant direction, strength, thickness, and vertical and horizontal coherence wavelengths of the surrounding

During remagnetization, chemical changes limited to moderate grain growth from pre-existing single domain (SD) grains do not modify the palaeomagnetic direction carried by these grains. Palaeomagnetic direction from new SD grains, on the contrary, is that of the magnetic field during remagnetization. The resulting direction becomes intermediate between the directions carried by previous and new SD grains, as it appears

We report magnetic hysteresis and back-field demagnetization data measured at 10° intervals of the angle ψ between the applied field H and the long (magnetically easy) axes of aligned elongated single-domain iron particles electrodeposited in regularly spaced surface pores in an Al substrate. Our three samples have identical particle diameters, d = 17 nm, but varying axial ratios l/d and

This paper presents a systematic micromagnetic analysis on spin valve GMR memory elements. It is found that for submicron size spin valve elements, edge demagnetization field, arising from the pinned layer, results in significant magnetization curling at the end edges of the free layer. This edge demagnetization phenomenon yields significant degradation of device performance. It is proposed that by making

Palaeomagnetic and biostratigraphic data were obtained for the latest Ladinian and most of the Carnian (Botneheia Formation to basal Kapp Toscana Group), from two sections in central Spitsbergen (Svalbard archipelago). Thermal and alternating field (AF) demagnetization reveals a magnetization of both normal and reversed polarities. The mean directions pass reversal and fold tests and are similar to other European Late