Micromagnetism–Microstructure Relations and the Hysteresis Loop

Abstract

Magnetic materials are widely used in many (modern) application fields ranging from electrical engineering, car industry and energy technique to sensor systems, high‐density recording and applications in medicine and biology. For a technological progress in these fields and for an application‐oriented magnet design the characteristic magnetic properties of the hysteresis loop are of great importance. Their steady improvement brings about in particular a continuous miniaturization of magnetic devices (hard magnetic materials) and a continuous reduction of energy losses during energy transmission (soft magnetic materials) leading to innovations in many new application fields and consequently to a rapid growth of the worldwide market. Modern high‐quality magnets are based on both optimized microstructures (including defect structures) and compounds with outstanding intrinsic material parameters. Optimized microstructures are composed of amorphous regions and/or ensembles of small magnetic grains with length scales varying from nm to cm. These extrinsic magnetic properties can be controlled by the choice of the alloy composition from the phase diagram (including small amounts of additives) and by the processing route as e.g. sintering, rapid quenching, sputtering or molecular beam epitaxy (including thermal and mechanical treatments). The detailed analysis of microstructure‐magnetic property relationships by means of different high‐resolution electron microscopy techniques and magnetic hysteresis loop measurements in combination with the theory of micromagnetism allows a quantitative interpretation of magnetization processes responsible for magnetic softening/hardening. This provides general rules for a successful specific tailoring of optimized characteristic magnetic properties of the hysteresis loop in the whole ferromagnetic (or ferrimagnetic) temperature range.

The Field-Dependent Magnetic Viscosity of FeNdB Permanent Magnets

“…This behavior can be explained by the imperfect microstructure of the sintered material. The grains of the material exhibit regions at the grain boundary where the hard magnetic properties are lowered and the demagnetization is facilitated in the presence of an applied opposing field [32,33]. Due to this fact, grains with larger regions of defects, i.e., where the demagnetization of the grain begins within the activation volume, are already demagnetized at weaker applied fields than in grains with smaller regions of magnetic defects.…”

Зарождение Магнитных Неоднородностей На Уединенных Дефектах Ферромагнетика

“…Интересно отметить, что данная ситуация не характерна для модели дефекта с негладким профилем, а вместе с тем -и для пластинчатого магнитного включения, так что исследования, основанные на допущениях этих простейших моделей, обречены на неполноту. Кроме того, для последних двух моделей дефектов можно утверждать, что для крупных дефектов, дающих наибольший вклад в технические характеристики материала, однородное распределение намагниченности в их области крайне маловероятно, в то время как 0 • -ДГ2, являясь метастабильным состоянием, может дать основной вклад в гистерезисные явления, которые являются доминирующими при перемагничивании изучаемых образцов [1].…”

“…Реальные магнетики отличаются от их идеализированных моделей прежде всего тем, что в них присутствуют различного рода дефекты, нарушающие их трансляционную инвариантность [1]. Это сказывается на их свойствах и, в частности, влияет на некоторые важные в техническом плане характеристики материала.…”

Model for domain wall pinning by randomly distributed nanosized defects in ultrathin magnetic films

“…In particular, for a coercive field of a zero thickness DW pinned by a random array of inhomogeneities the scaling laws were found in both weak and strong pinning regimes [8][9][10]. Although stationary DW pinning and depinning mechanisms seem to be well understood [11,12], rigorous theoretical results on DW pinning by nanosized defects in ultrathin films are scarce. Only few theoretical investigations relate to the case where defects are nothing more than the magnetic atoms themselves; this situation is referred to as the Peierls potential case [13].…”