We show that the interaction of the magnetic subsystem of a curved magnet with the magnet curvature results in the coupling of a topologically nontrivial magnetization pattern and topology of the ...object. The mechanism of this coupling is explored and illustrated by an example of a ferromagnetic Möbius ring, where a topologically induced domain wall appears as a ground state in the case of strong easy-normal anisotropy. For the Möbius geometry, the curvilinear form of the exchange interaction produces an additional effective Dzyaloshinskii-like term which leads to the coupling of the magnetochirality of the domain wall and chirality of the Möbius ring. Two types of domain walls are found, transversal and longitudinal, which are oriented across and along the Möbius ring, respectively. In both cases, the effect of magnetochirality symmetry breaking is established. The dependence of the ground state of the Möbius ring on its geometrical parameters and on the value of the easy-normal anisotropy is explored numerically.
Thin films of the magnetoelectric insulator α‐Cr2O3 are technologically relevant for energy‐efficient magnetic memory devices controlled by electric fields. In contrast to single crystals, the ...quality of thin Cr2O3 films is usually compromised by the presence of point defects and their agglomerations at grain boundaries, putting into question their application potential. Here, the impact of the defect nanostructure, including sparse small‐volume defects and their complexes is studied on the magnetic properties of Cr2O3 thin films. By tuning the deposition temperature, the type, size, and relative concentration of defects is tailored, which is analyzed using the positron annihilation spectroscopy complemented with electron microscopy studies. The structural characterization is correlated with magnetotransport measurements and nitrogen‐vacancy microscopy of antiferromagnetic domain patterns. Defects pin antiferromagnetic domain walls and stabilize complex multidomain states with a domain size in the sub‐micrometer range. Despite their influence on the domain configuration, neither small open‐volume defects nor grain boundaries in Cr2O3 thin films affect the Néel temperature in a broad range of deposition parameters. The results pave the way toward the realization of spin‐orbitronic devices where magnetic domain patterns can be tailored based on defect nanostructures without affecting their operation temperature.
The defect nanostructure of α‐Cr2O3 relying on positron annihilation spectroscopy and transmission electron microscopy is studied. These structural data are correlated with the magnetotransport spin Hall magnetoresistance measurements and direct imaging of antiferromagnetic domains using nitrogen‐vacancy scanning magnetometry. The impact of structural defects on magnetic microstructure and spin‐orbitronic properties of Cr2O3 thin films is discussed.
The orientation of a chiral magnetic domain wall in a racetrack determines its dynamical properties. In equilibrium, magnetic domain walls are expected to be oriented perpendicular to the stripe ...axis. We demonstrate the appearance of a unidirectional domain wall tilt in out-of-plane magnetized stripes with biaxial anisotropy and Dzyaloshinskii-Moriya interaction (DMI). The tilt is a result of the interplay between the in-plane easy-axis anisotropy and DMI. We show that the additional anisotropy and DMI prefer different domain wall structure: anisotropy links the magnetization azimuthal angle inside the domain wall with the anisotropy direction in contrast to DMI, which prefers the magnetization perpendicular to the domain wall. Their balance with the energy gain due to domain wall extension defines the equilibrium magnetization the domain wall tilting. We demonstrate that the Walker field and the corresponding Walker velocity of the domain wall can be enhanced in the system supporting tilted walls.
•Ground states in magnetic spherical shells form two out-of-surface vortices.•Depending on geometrical parameters onion and whirligig states can be distinguished.•A continuous phase transition takes ...place between onion and whirligig ground states.•The magnetization state of infinitely small spherical shell is never homogeneous.
Equilibrium magnetization states in spherical shells of a magnetically soft ferromagnet form two out-of-surface vortices with codirectionally magnetized vortex cores at the sphere poles: (i) a whirligig state with the in-surface magnetization oriented along parallels is typical for thick shells; (ii) a three dimensional onion state with the in-surface meridional direction of the magnetization is realized in thin shells. The geometry of spherical shell prohibits an existence of spatially homogeneous magnetization distribution, even in the case of small sample radii. By varying geometrical parameters a continuous phase transition between the whirligig and onion states takes place. The detailed analytical description of the phase diagram is well confirmed by micromagnetic simulations.
Manipulation of the domain wall propagation in magnetic wires is a key practical task for a number of devices including racetrack memory and magnetic logic. Recently, curvilinear effects emerged as ...an efficient mean to impact substantially the statics and dynamics of magnetic textures. Here, we demonstrate that the curvilinear form of the exchange interaction of a magnetic helix results in an effective anisotropy term and Dzyaloshinskii-Moriya interaction with a complete set of Lifshitz invariants for a one-dimensional system. In contrast to their planar counterparts, the geometrically induced modifications of the static magnetic texture of the domain walls in magnetic helices offer unconventional means to control the wall dynamics relying on spin-orbit Rashba torque. The chiral symmetry breaking due to the Dzyaloshinskii-Moriya interaction leads to the opposite directions of the domain wall motion in left- or right-handed helices. Furthermore, for the magnetic helices, the emergent effective anisotropy term and Dzyaloshinskii-Moriya interaction can be attributed to the clear geometrical parameters like curvature and torsion offering intuitive understanding of the complex curvilinear effects in magnetism.
Bloch point structure in a magnetic nanosphere Pylypovskyi, Oleksandr V.; Sheka, Denis D.; Gaididei, Yuri
Physical review. B, Condensed matter and materials physics,
6/2012, Letnik:
85, Številka:
22
Journal Article
Recenzirano
Odprti dostop
A Bloch point singularity can form a metastable state in a magnetic nanosphere. We classify possible types of Bloch points and analytically derive the shape of the magnetization distribution for ...different Bloch points. We show that an external gradient field can stabilize the Bloch point: The shape of the Bloch point becomes radially dependent. We compute the magnetization structure of the nanosphere, which is in good agreement with performed spin-lattice simulations.
The concept of curvature and chirality in space and time are foundational for the understanding of the organic life and formation of matter in the Universe. Chiral interactions but also curvature ...effects are tacitly accepted to be local. A prototypical condensed matter example is a local spin-orbit- or curvature-induced Rashba or Dzyaloshinskii-Moriya interactions. Here, we introduce a chiral effect, which is essentially nonlocal and resembles itself even in static spin textures living in curvilinear magnetic nanoshells. Its physical origin is the nonlocal magnetostatic interaction. To identify this interaction, we put forth a self-consistent micromagnetic framework of curvilinear magnetism. Understanding of the nonlocal physics of curved magnetic shells requires a curvature-induced geometrical charge, which couples the magnetic sub-system with the curvilinear geometry. The chiral interaction brings about a nonlocal chiral symmetry breaking effect: it introduces handedness in an intrinsically achiral material and enables the design of magnetolectric and ferrotoroidic responses.Curvature effects in a magnetic system are usually described by treating local and non-local interactions separately. Here, the authors develop a theory of curvilinear micromagnetism and report a non-local chiral interaction which is absent in flat systems.
Thin films of the magnetoelectric insulator α-Cr
O
are technologically relevant for energy-efficient magnetic memory devices controlled by electric fields. In contrast to single crystals, the quality ...of thin Cr
O
films is usually compromised by the presence of point defects and their agglomerations at grain boundaries, putting into question their application potential. Here, the impact of the defect nanostructure, including sparse small-volume defects and their complexes is studied on the magnetic properties of Cr
O
thin films. By tuning the deposition temperature, the type, size, and relative concentration of defects is tailored, which is analyzed using the positron annihilation spectroscopy complemented with electron microscopy studies. The structural characterization is correlated with magnetotransport measurements and nitrogen-vacancy microscopy of antiferromagnetic domain patterns. Defects pin antiferromagnetic domain walls and stabilize complex multidomain states with a domain size in the sub-micrometer range. Despite their influence on the domain configuration, neither small open-volume defects nor grain boundaries in Cr
O
thin films affect the Néel temperature in a broad range of deposition parameters. The results pave the way toward the realization of spin-orbitronic devices where magnetic domain patterns can be tailored based on defect nanostructures without affecting their operation temperature.
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