Ultrafast transfer of magnetization on magnetic sublattices in half-metallic Co2MnGe heusler alloys

Heusler alloys are exciting materials for future applications because they display a wide range of tunable electronic and magnetic interactions such as metallicity, ferromagnetism, superconductivity, and giant magneto-resistance. However, laser-induced spin dynamics in heuslers were expected to be slower than in conventional metallic ferromagnets, due to the presence of a blocked spin channel. Here we directly observe ultrafast spin transfer from one magnetic sublattice to another in half-metallic heusler alloy Co2MnGe, that occurs on the timescale of the femtosecond laser excitation. Ultrafast high harmonic pulses make it possible to simultaneously record the element-specific magnetic dynamics of Co and Mn as the material undergoes demagnetization. The magnetization of Co is transiently enhanced by 10% within 60 fs, while that of Mn rapidly quenches. By comparing our data to density functional theory, we show that optical excitation can directly transfer spin from one magnetic sub-lattice to another, due to spin-polarized optical excitation pathways. The observed transient enhancement of ferromagnetic ordering demonstrates fast manipulation of spin by light, thus providing a path towards spintronics logic devices that can operate on femtosecond or even attosecond timescales.