Microwave spectroscopy of the low-temperature skyrmion state in Cu2OSeO3

Abstract

In the cubic chiral magnet Cu 2 OSeO 3 a low-temperature skyrmion state (LTS) and a concomitant tilted conical state are observed for magnetic fields parallel to 100 . In this work, we report on the dynamic resonances of these novel magnetic states. After promoting the nucleation of the LTS by means of field cycling, we apply broadband microwave spectroscopy in two experimental geometries that provide either predominantly in-plane or out-of-plane excitation. By comparing the results to linear spin-wave theory, we clearly identify resonant modes associated with the tilted conical state, the gyrational and breathing modes associated with the LTS, as well as the hybridization of the breathing mode with a dark octupole gyration mode mediated by the magnetocrystalline anisotropies. Most intriguingly, our findings suggest that under decreasing fields the hexagonal skyrmion lattice becomes unstable with respect to an oblique deformation, reflected in the formation of elongated skyrmions.

Confined dipole and exchange spin waves in a bulk chiral magnet with Dzyaloshinskii-Moriya interaction

“…In order to make use of the nontrivial magnonic properties, finite wave-vector k excitations in chiral magnets are strongly demanded. The spin dynamics in bulk chiral magnets with lateral dimension up to millimeters have been investigated experimentally [14][15][16][17][18][19][20][21] but mostly focusing on a wave vector k = 0. To explore the spin wave excitation with finite k, focused ion beam patterning was utilized to shape the chiral magnets into lamella and to flip them onto microstructured coplanar waveguides (CPWs) [9,13].…”

“…In thin films of the * dirk.grundler@epfl.ch chiral magnet FeGe, an oscillating factor exp(−iQz) was introduced when the ferromagnetic resonance (FMR) at k = 0 and perpendicular standing spin waves with finite k were interpreted, where Q is the pitch vector in a chiral magnet [35]. Standing spin waves were assumed in bulk Cu 2 OSeO 3 [18,19] but their characteristics remained unexplored.…”