Observation of spin transfer torques in the transverse magnetic susceptibility of the Skyrmion lattice phase of MnSi

In the Skyrmion lattice phase of MnSi the observation of sizeable spin transfer torques [1-3] promises easy experimental access to the precise qualitative and quantitative form of the Landau Lifshitz Gilbert equation. We report measurements of the transverse magnetic susceptibility, $\chi_{\perp}$, in the skyrmion lattice phase of MnSi. Our measurements show a distinct increase of $\chi_{\perp}$ with increasing current density around the critical current density $j_\mathrm{c}$. We further find a siszable dissipative part of $\chi_{\perp}$ evolving above $j_\mathrm{c}$. We discuss the broader implications of our experimental findings, which provide, for the first time, a direct link between a thermodynamic property and the effects of spin transfer torques in skyrmion lattices. \newline [1] F. Jonietz et al., Science \textbf{330}, 1648 (2010) \newline [2] T. Schulz et al., Nat. Phys. \textbf{8}, 301 (2012) \newline [2] K. Everschor et al., Phys. Rev. B \textbf{86}, 054432 (2012)