Magnetic excitations are at the heart of the dynamics of spin systems. Here, we report on the first observation of two magnetic excitations, i.e., magnetic phasons in non-collinear spin textures and magnon-polarons resulting from coupling of acoustic phonons and magnons.
The nanoscopic magnetic texture forming in a monolayer of Fe/Ir(111) is spatially modulated and uniaxially incommensurate with respect to the atomic lattice. As a consequence, a low-energy magnetic excitation is expected that corresponds to the sliding of the texture along the incommensurate direction, i.e., a phason mode. Using spin-polarized STM, the phason has been experimentally observed and can be excited by the tunneling current.
Fe3GeTe2 (FGT) is a ferromagnetic van der Waals material that hosts besides Skyrmions also collective excitations in form of magnons hybridized with acoustic phonons. We study the dynamic coupling of these two excitations in FGT using STM at ultra-low temperatures. A strong interaction between magnons and acoustic phonons leads to avoided band crossings and hybridization between the magnonic and phononic bands, which lifts the constrains set by the selection rules for their individual excitation by electrons and boosts the excitation cross sections. Our findings provide a platform for designing the properties of dynamic magnon-phonon coupling in two-dimensional materials in form of phonon-localization in magnetic domain walls or magnon localization by strain fields.

Altermagnets are an emerging class of collinear magnets featuring two qualities previously believed to be incompatible: a vanishingly small net magnetization and spin-polarized electronic band structures. These features are well-understood from the unusual symmetry properties of altermagnets, which can be related to an underlying magnetic multipolar ordering in the systems. In this talk, I will describe how such multipolar character governs transport phenomena such as the anomalous Hall effect and spin transports, shedding light on the origin of the unique characters of altermagnets.