Spin-Frame Field Theory of a Three-Sublattice Antiferromagnet.

We present a nonlinear field theory of a three-sublattice hexagonal antiferromagnet. The order parameter is the spin frame, an orthogonal triplet of vectors related to sublattice magnetizations and spin chirality. The exchange energy, quadratic in spin-frame gradients, has three coupling constants, only two of which manifest themselves in the bulk.

Mechanics of a ferromagnetic domain wall.

This paper gives a pedagogical introduction to the mechanics of ferromagnetic solitons. We start with the dynamics of a single spin and develop all the tools required for the description of the dynamics of solitons in a ferromagnet.

Unified theory of spin and charge in a ferromagnet.

We derive a unified theory of spin and charge degrees of freedom in a ferromagnet. The spin-transfer torque and spin electromotive force are examined from the coarse-grained perspective of collective coordinates. The resulting equations of motion reflect a balance of conservative, gyroscopic (Berry-phase), and dissipative forces.

Noncollinear Ground State from a Four-Spin Chiral Exchange in a Tetrahedral Magnet.

We propose a quartic chiral term m_{x}m_{y}m_{z}∇·m for the energy density of a cubic ferromagnet with broken parity symmetry (point group T_{d}). We demonstrate that this interaction causes a phase transition from a collinear ferromagnetic state to a noncollinear magnetic cone ground state provided its strength exceeds the geometric mean of magnetic exchange and cubic anisotropy. The corresponding noncollinear ground state may also be additionally stabilized by an external magnetic field pointing along certain crystallographic directions.

Antichiral spin order, its soft modes, and their hybridization with phonons in the topological semimetal .

We report the magnetic structure and spin excitations of , a breathing kagome antiferromagnet with transport anomalies attributed to Weyl nodes. Using polarized neutron diffraction, we show the magnetic order is a coplanar state belonging to a irreducible representation, which can be described as a perfect 120° antichiral structure with a moment of , superimposed with weak collinear ferromagnetism. Inelastic neutron scattering shows three collective excitations at , , and .