Nucleation and pinning of magnetic domains at Co7Sm2 precipitates in Co5Sm crystals

Abstract

By means of the magneto-optical Kerr effect the domain configuration in Co,Sm-crystals is investigated in dependence on the applied magnetic field. The observed change of the domain structure is interpreted in terms of a micromagnetic theory for the magnetization curve of uniaxial single crystals. The displacement of domain walls took place at an initial field of 265 Oe which is interpreted as the intrinsic coercive field due to the Peierls potential and randomly distributed lattice defects. The density of the interaction energy per extension of the wall is determined to be E, ] / g L = 30 erg/cm4 in the case of a rigid wall. The nucleation of reversed domains is observed in the phase boundary between precipitate and matrix. Furthermore precipitates in grain bounda,ries are found to act as sources of nucleation centres. These results are interpreted by the nucleation of reversed domains in regions of low crystal onisotropy or of irregular precipitate-surface. Ilittels des magnetooptischenKerreffekts wird die Domanenstruktur in Co,Sm-Kristallen in Abhangigkeit vom auderen Magnetfeld untersucht. Die beobachtete Anderung der Domlnenstruktur wird durch eine mikromagnetische Theorie fur die Magnetisierungskurve eines einachsigen Einkristalls interpretiert. Die Bewegung der Domanenwande tritt erst ab einer Feldstarke von 265 Oe ein. Dies entspricht einer inneren Koerzitivfeldstarke, die durch das Peierlspotential und statistisch verteilte Gitterfehler hervorgerufen wird. Die Dichte der Wechselwirkungsenergie pro Snsdehnnng der Wand wird fur den Fall einer ebenen Wand als E, ) 2 L = 30 erg/cm4 bestimnit. Die Nukleation der Domanen wird im Phasenubergang zwischen Ausscheidung und Matrix beobachtct. Des weiteren konnen Ausscheidungen in Korngrenzen als niukleationszentren nachgewiesen werden. Diese Ergebnisse werden durch die Nakleation von Domanen in Bereichen niedriger Kristallanisotropie oder ungleichformiger Ausscheidungsoberfllche interpreticrt. l) Co,Sm alloys wcrc produced from 99.995 Yn pure cobalt and 99.9% pure samarium

Magnetic nanostructures for advanced technologies: fabrication, metrology and challenges

“…Once the nucleation event occurs, the created domain wall quickly propagates in a nanostructure, since this is a high energy state of the system. However, known pinning sites such as voids and magnetic or non-magnetic inclusions [290], grain boundaries [291,292] and edges [293] can inhibit further expansion of the reversed domain. In general, the choice of nucleating a new domain or dislodging an existing domain wall from a pinning site comes down to overcoming the lowest of the energy barriers present.…”

Studies of the domain structure of anisotropic sintered SmCo5 permanent magnets

“…[47,50,53,[59][60][61] and the values obtained are in the range 61-150 erg/cm 2 . (It was also estimated theoretically in Refs.…”