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Description
To extend μSR to driven samples, we employ a microwave stimulus to excite the sample by ferromagnetic resonance (FMR) and probe the resultant effect with the muon. The experiments were performed on the helimagnet Cu$_2$OSeO$_3$, which exhibits distinct FMR and μSR signatures throughout its magnetic phase diagram. FMR excitations in the helical state cause precession, which is characterized by a dynamic component $M_\mathrm{uw}$ and an associated reduction in static moment $\Delta M$ (Fig. 1a). Both LF- and TF-μSR data exhibit a reduction in the frequency $\nu_\mathrm{fast}$ of the fast-oscillation component, which we attribute to the reduction of the static moment $\Delta M$ (Fig. 1b for LF).
Besides $\Delta M$ and $M_\mathrm{uw}$, a MHz precession of the entire magnetic helix akin to a screw has been predicted theoretically under FMR excitation [1]. While invisible in ordinary FMR, our combined FMR-μSR approach is well suited for detection of this technologically relevant mode. Our preliminary LF data indicate a small change in the damping rate $\sigma_\mathrm{slow}$ of the slow decay component (see Fig. 1c). Further experiments at lower temperature and stronger microwave drive were, however, not supportive of such a screw mode.
[1] N. del Ser, L. Heinen, A. Rosch, SciPost Phys. 11, 009 (2021).
| andrin.doll@psi.ch | |
| Funding Agency | PSI |
