We study pumping of magnons to the Dirac points of magnon's Brillouin zone of a ferromagnet on a honeycomb lattice. In particular, we consider second-order Suhl process, when due to interaction between magnons, a pair of magnons is created due to absorption of two electromagnetic wave quanta. We introduce a bosonic analog of the Cooper ladder for the magnon pair, which is shown to enhance the pairing of magnons at the Dirac points. As a result of pairing of the Dirac magnons, the system becomes unstable towards formation of a magnetic state with zero magnetization—the Dirac magnon paired state. In this case the resonant frequency of the pump equals to that of energy of the Dirac points. Our estimates suggest that the Dirac magnon paired state can be found in the CrBr3 or CrCl3 ferromagnet below in vicinity of the Curie temperature.

We theoretically describe a mechanism of low-field linear magnetoconductivity in helical magnetic metals. Two ingredients for the mechanism in three-dimensional metals are identified to be the spin-orbit coupling and momentum-dependent ferromagnetic exchange interaction. We propose and study a number of minimal theoretical models which have linear magnetoconductivity and discuss their implications for recent experiments.

We study Berry curvature driven and Zeeman magnetic field dependent electric current responses of two-dimensional electron system with spin-orbit coupling. A nondissipative component of the electric current occurring in the applied in-plane magnetic field is described. This component is transverse to the electric field, odd in the magnetic field, and depends only on one particular direction of the magnetic field defined by the spin-orbit coupling. We show that the effect can be observed in a number of systems with C-3v symmetry.