Coercivity in hard magnetic materials
type: Dataset
description: Magnetization reversal in NdFeB-type permanent magnets was studied in this thesis, based on both global (magnetometry) and local (magnetic force microscopy) experimental techniques. Two types of samples were analyzed: bulk magnets of which magnetic properties are greatly improved as a result of NdCu infiltration along the grain boundaries (samples provided by Toyota Motor Corporation) and thick film magnets with different microstructures and thus different coercive fields. The temperature dependence of the coercive field and that of the activation volume were analyzed in the framework of two models: the micromagnetic and the global model. The derived values of the two main parameters characterizing coercivity (N representing demagnetizing field effects and α linking the coercive field to the intrinsic magnetic properties of the hard phase) indicate that, in bulk magnets, the difference in coercivity between different samples is related mainly to N whereas in films the parameter alfa plays the leading role. The activation volume derived from magnetic after effect measurements is similar for all bulk samples at a given temperature. On the opposite, it varies in the case of films : the higher the coercive field, the smaller the activation volume. Altogether, it is concluded that the magnetic properties within the activation volume are close to those of the main phase. The link between microstructure and coercivity was studied in thick films, using magnetic force microscopy. Imaging of films that present different microstructures was performed in different remanent states along the hysteresis cycle. Interaction domains were observed in the case of films with lower coercive field. In such low coercivity films, as well as in medium coercivity ones, magnetization reversal is dominated by domain wall propagation, instead of nucleation + propagation in high coercivity films.
identifier: NNT: 2013GRENY014
issued: 2026-05-06T03:45:07.301957
language: fr
modified: 2026-05-06T03:45:07.301961
contact point: Organization
  fn: CCSD
keyword: aimant-permanent
keyword: coercitivite
keyword: coercivity
keyword: couches-magnetiques-dures
keyword: hard-magnetic-films
keyword: infoeu-reposemanticsdoctoralthesis
keyword: magnetization-reversal-mechanism
keyword: mecanisme-de-renversement-daimantation
keyword: permanent-magnet
keyword: physcondcm-genphysics-physicscondensed-matter-cond-matother-cond-matother
keyword: theses
landing page: https://theses.hal.science/tel-00952842

Coercivity in hard magnetic materials
type: Distribution
format: HTML
issued: 2026-05-06T03:45:07.325742
modified: 2026-05-06T03:45:07.288021
access URL: https://theses.hal.science/tel-00952842

test_moissonnage_selune
type: Agent