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Physics of Nanomagnets
Published in Klaus D. Sattler, 21st Century Nanoscience – A Handbook, 2020
Ralph Skomski, Balamurugan Balasubramanian, D. J. Sellmyer
The spins of Figure 18.2a are all collinear (parallel or antiparallel). There are also many noncollinear spin structures, one of which is shown in Figure 18.2b. Zero-temperature or ‘frozen’ spin structures of this type are found in spin glasses and amorphous magnets. A similar spin structure is also found above the Curie temperature, but with one important difference: above Tc, the spins are not frozen but rotate rapidly. The difference is similar between that of a glass and a liquid, where snapshots of the atomic positions look similar but rapidly change with time in the case of liquids. Figure 18.2c shows a typical micromagnetic spin structure, namely a domain wall. The basic atomic spin structure is ferromagnetic, so that neighboring spins are nearly parallel and M(r) changes only slowly. Other noncollinear spin structures helical, characterized by a wave vector k, or canted, for example, due to Dzyaloshinskii–Moriya interactions. If the term “spin structure” is used without specification, it refers to the atomic spin structure, as contrasted to finite-temperature and micromagnetic spin structures.
Magneto-ionic suppression of magnetic vortices
Published in Science and Technology of Advanced Materials, 2021
Yu Chen, Aliona Nicolenco, Pau Molet, Agustin Mihi, Eva Pellicer, Jordi Sort
Figure 3 illustrates the evolution of the simulated spin configurations corresponding to different values of applied magnetic field for rough Co nanopillars with the geometry depicted in Supporting Figure S2(f) (i.e. magnetization reversal occurring through vortex spin structure). When the magnetic field is decreased from saturation (1), the magnetic vortex nucleates at around 1000 Oe (2–3). This is accompanied by an abrupt decrease in the average dot magnetization. As the magnetic field is further decreased the vortex core progressively displaces towards the center of the disk and at zero magnetic field all the spins follow the circular geometry of the disk (4). When the magnetic field reaches the annihilation field (5), the vortex vanishes completely (6). This occurs at around 2020 Oe. This process stabilizes the single-domain state with negative orientation.