Title: Sensing spin currents that are generated in momentum and real space 

Discussion:

Magnetic Skyrmions are attractive for ultra-dense data storage applications such as the racetrack memory (RM). Recently, frustration in ferromagnetic (FM) crystals was predicted of being capable of providing the topological protection of the Skyrmion without relying on the DMI and the effect was immediately discovered in Fe3Sn2 bulk crystals. Surprisingly, these Skyrmions survive even at room temperature and are controllable by electrical current. These advances illustrate the exceptional technological potential of the Fe3Sn2 system. In this work, we study the dynamics of a bulk Fe3Sn2 crystal through an optically probed spin torque driven ferromagnetic resonance (OSTFMR) technique. We excite the magnetic system by passing RF current through the crystal where the charge current converts into spin-polarized current through the spin Hall effect. From the dynamical response we identify the rotational (clock-wise or counter-clock-wise) and the translational (breathing) modes and reconstruct the phase transitions of the magnetic skyrmion texture. Using this technique, we follow the evolution of the two modes as a function of the externally applied magnetic field and map the magnetic phase transitions of the Fe3Sn2 crystal. A complementary numberical micromagnetic simulations confirms our results.