45 research outputs found
Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states
Magnetic chiral skyrmions are vortex like spin structures that appear as
stable or meta-stable states in magnetic materials due to the interplay between
the symmetric and antisymmetric exchange interactions, applied magnetic field
and/or uniaxial anisotropy. Their small size and internal stability make them
prospective objects for data storage but for this, the controlled switching
between skyrmion states of opposite polarity and topological charge is
essential. Here we present a study of magnetic skyrmion switching by an applied
magnetic field pulse based on a discrete model of classical spins and atomistic
spin dynamics. We found a finite range of coupling parameters corresponding to
the coexistence of two degenerate isolated skyrmions characterized by mutually
inverted spin structures with opposite polarity and topological charge. We
demonstrate how for a wide range of material parameters a short inclined
magnetic field pulse can initiate the reliable switching between these states
at GHz rates. Detailed analysis of the switching mechanism revealed the complex
path of the system accompanied with the excitation of a chiral-achiral meron
pair and the formation of an achiral skyrmion
Second-order topological superconductor via noncollinear magnetic texture
We put forth a theoretical framework for engineering a two-dimensional (2D)
second-order topological superconductor (SOTSC) by utilizing a heterostructure:
incorporating noncollinear magnetic textures between an s-wave superconductor
and a 2D quantum spin Hall insulator. It stabilizes the higher order
topological superconducting phase, resulting in Majorana corner modes (MCMs) at
four corners of a 2D domain. The calculated non-zero quadrupole moment
characterizes the bulk topology. Subsequently, through a unitary
transformation, an effective low-energy Hamiltonian reveals the effects of
magnetic textures, resulting in an effective in-plane Zeeman field and
spin-orbit coupling. This approach provides a qualitative depiction of the
topological phase, substantiated by numerical validation within exact
real-space model. Analytically calculated effective pairings in the bulk
illuminate the microscopic behavior of the SOTSC. The comprehension of MCM
emergence is aided by a low-energy edge theory, which is attributed to the
interplay between effective pairings of (px + py )-type and (px + ipy )-type.
Our extensive study paves the way for practically attaining the SOTSC phase by
integrating noncollinear magnetic textures
Role of Berry phase theory for describing orbital magnetism: From magnetic heterostructures to topological orbital ferromagnets
We address the importance of the modern theory of orbital magnetization for
spintronics. Based on an all-electron first-principles approach, we demonstrate
that the predictive power of the routinely employed "atom-centered"
approximation is limited to materials like elemental bulk ferromagnets, while
the application of the modern theory of orbital magnetization is crucial in
chemically or structurally inhomogeneous systems such as magnetic thin films,
and materials exhibiting non-trivial topology in reciprocal and real
space,~e.g.,~Chern insulators or non-collinear systems. We find that the modern
theory is particularly crucial for describing magnetism in a class of materials
that we suggest here topological orbital ferromagnets.Comment: 5 pages, 4 figure
Interlayer Exchange Coupling: A General Scheme Turning Chiral Magnets into Magnetic Multilayers Carrying Atomic-Scale Skyrmions
We report on a general principle using interlayer exchange coupling to extend the regime of chiral magnetic films in which stable or metastable magnetic Skyrmions can appear at a zero magnetic field. We verify this concept on the basis of a first-principles model for a Mn monolayer on a W(001) substrate, a prototype chiral magnet for which the atomic-scale magnetic texture is determined by the frustration of exchange interactions, impossible to unwind by laboratory magnetic fields. By means of ab initio calculations for the Mn/Wm/Con/Pt/W(001) multilayer system we show that for certain thicknesses m of the W spacer and n of the Co reference layer, the effective field of the reference layer fully substitutes the required magnetic field for Skyrmion formation
K(2)O(2): The most stable oxide of K
We have analyzed the stability of various oxides of K and find that K(2)O(2) is the most stable one. The additional stability is traced to the presence of oxygen dimers in K(2)O(2) which interact to form molecular orbitals. Other oxides such as KO(2) and KO(3) which also have dimers/trimers of oxygens are found to be less stable. This is traced to the shorter O-O bonds that one finds in them which gives rise to a significant coulomb repulsion between the electrons on the oxygen atoms making up the dimer/trimer, making them less stable
K<sub>2</sub>O<sub>2</sub>: the most stable oxide of K
We have analyzed the stability of various oxides of K and find that K<sub>2</sub>O<sub>2</sub> is the most stable one. The additional stability is traced to the presence of oxygen dimers in K<sub>2</sub>O<sub>2</sub> which interact to form molecular orbitals. Other oxides such as KO<sub>2</sub> and KO<sub>3</sub> which also have dimers/trimers of oxygens are found to be less stable. This is traced to the shorter O–O bonds that one finds in them which gives rise to a significant coulomb repulsion between the electrons on the oxygen atoms making up the dimer/trimer, making them less stable