A new class of nodal stationary states in 2D Heisenberg ferromagnet

A new class of nodal topological excitations in a two-dimensional Heisenberg model is studied. The solutions correspond to a nodal singular point of the gradient field of the azimuthal angle. An analytical solution found for the isotropic case. An effect of in-plane exchange anisotropy is studied numerically. It results in solutions which are analogues of the conventional out-of-plane solitons in the two-dimensional magnets.Comment: 5 figure

Theory of spin current in chiral helimagnet

We give detailed description of the transport spin current in the chiral helimagnet. Under the static magnetic field applied perpendicular to the helical axis, the magnetic kink crystal (chiral soliton lattice) is formed. Once the kink crystal begins to move under the Galilean boost, the spin-density accumulation occurs inside each kink and there emerges periodic arrays of the induced magnetic dipoles carrying the transport spin current. The coherent motion of the kink crystal dynamically generates the spontaneous demagnetization field. This mechanism is analogous to the D\"{o}ring-Becker-Kittel mechanism of the domain wall motion in ferromagnets. To describe the kink crystal motion, we took account of not only the tangential $\phi$-fluctuations but the longitudinal $\theta$-fluctuations around the helimagnetic configuration. Based on the collective coordinate method and the Dirac's canonical formulation for the singular Lagrangian system, we derived the closed formulae for the mass, spin current and induced magnetic dipole moment accompanied with the kink crystal motion. To materialize the theoretical model presented here, symmetry-adapted material synthesis would be required, where the interplay of crystallographic and magnetic chirality plays a key role there.Comment: 16 pages, 6 figures, to be published in Phys. Rev.

Topological stripelike coreless textures with inner incommensurability in two-dimensional Heisenberg antiferromagnet

For two-dimensional Heisenberg antiferromagnet we present an analysis of topological coreless excitations having a stripe form. These textures are characterized by singularities at boundaries. A detailed classification of the stripe textures results in a certain analogy with the coreless excitations in $^3He-A$ phase: Mermin-Ho and Anderson-Toulouse coreless vortices. The excitations of the last type may have a low bulk energy. The stripe textures may be observed as an occurrence of short-range incommensurate order in the antiferromagnetic environment

Bose-Einstein condensation of semi-hard bosons in S=1 dimerized organic compound F2PNNNO

An analysis of the energy spectrum and the magnetization curve of two-dimensional organic antiferromagnet F2PNNNO with a spin-one dimerized structure shows that a behavior of the compound in an external magnetic field can be explained within a lattice boson model with an extended Pauli's exclusion principle, i.e. no more than two bosons per a dimer. The unusual magnetization curve observed experimentally in the compound reflects a sequence of phase transitions intrinsic for a lattice boson system with strong on-site and inter-site repulsions due to a tuning of magnon density by the applied magnetic field

Hidden Galilean symmetry, conservation laws and emergence of spin current in the soliton sector of chiral helimagnet

Motivated by the spin current problem in chiral helimagnet, we rigorously elucidated the hidden Galilean invariance in the chiral XY model under the magnetic field. The Lie group analysis is applied to the differential equations of the continuum theory of the chiral helimagnet with the parity-violating Dzyaloshinskii-Morya coupling under a transversal magnetic field. Lie point symmetries and the invariant solutions under these symmetries are found. They present sliding solutions that come up as a consequence of breaking of both spin rotational symmetry by the external magnetic field and a parity violation due to the Dzyaloshinskii-Morya interaction. We found that variational symmetries are related with translations in space and time, the corresponding energy and momentum conservation laws are derived. We therefore succeeded in justifying the existence of the transport spin current in chiral helimagnet.Comment: 14 page

Generation of spin motive force in a soliton lattice

The generation of a spin motive force in a chiral helimagnet due to the action of two crossed magnetic fields is considered. The cases of pulsed and periodic magnetic fields directed along the helical axis under a perpendicular dc field are analyzed. It is shown that, in the case of a pulsed field, the spin motive force is related to dissipation, whereas in a periodic field, there is a reactive component that is not related to damping processes. © 2013 Pleiades Publishing, Ltd

Theory of standing spin waves in finite-size chiral spin soliton lattice

We present a theory of standing spin wave (SSW) in a monoaxial chiral helimagnet. Motivated by experimental findings on the magnetic field-dependence of the resonance frequency in thin films of Cr${}$Nb$_{3}$S${}_{6}$[Goncalves et al., Phys. Rev. B95, 104415 (2017)], we examine the SSW over a chiral soliton lattice (CSL) excited by an ac magnetic field applied parallel and perpendicular to the chiral axis. For this purpose, we generalize Kittel-Pincus theories of the SSW in ferromagnetic thin films to the case of non-collinear helimagnet with the surface end spins which are softly pinned by an anisotropy field. Consequently, we found there appear two types of modes. One is a Pincus mode which is composed of a long-period Bloch wave and a short-period ripple originated from the periodic structure of the CSL. Another is a short-period Kittel ripple excited by space-periodic perturbation which exists only in the case where the ac field is applied perpendicular the chiral axis. We demonstrate that the existence of the Pincus mode and the Kittel ripple is consistent with experimentally found double resonance profile.Comment: 17 pages, 14 figure

Transport magnetic currents driven by moving kink crystal in chiral helimagnets

We show that the bulk transport magnetic current is generated by the moving magnetic kink crystal (chiral soliton lattice) formed in the chiral helimagnet under the static magnetic field applied perpendicular to the helical axis. The current is caused by the non-equilibrium transport momentum with the kink mass being determined by the spin fluctuations around the kink crystal state. An emergence of the transport magnetic currents is then a consequence of the dynamical off-diagonal long range order along the helical axis. We derive an explicit formula for the inertial mass of the kink crystal and the current in the weak field limit.Comment: 5 pages, 3 figures, to appear in Phys. Rev.

Coherent sliding dynamics and spin motive force driven by crossed magnetic fields in a chiral helimagnet

We demonstrate that the chiral soliton lattice formed from a chiral helimagnet exhibits a coherent sliding motion when a time-dependent magnetic field is applied parallel to the helical axis, in addition to a static field perpendicular to the helical axis. To describe the coherent sliding, we use the collective coordinate method and a numerical analysis. We also show that the time-dependent sliding velocity causes a time-varying Berry cap which creates a spin motive force. A salient feature of the chiral soliton lattice is the appearance of a strongly amplified spin motive force which is directly proportional to the macroscopic number of solitons (magnetic kinks). © 2012 American Physical Society