Direct light-induced spin transfer between different elements in a spintronic Heusler material via femtosecond laser excitation

Heusler compounds are exciting materials for future spintronics applications because they display a wide range of tunable electronic and magnetic interactions such as metallicity, superconductivity, and giant magneto-resistance. We use a femtosecond light pulse to directly transfer spin polarization from one element to another in a half-metallic Heusler material, Co₂MnGe. This spin transfer initiates as soon as light is incident on the material, showing that we can transfer angular momentum between neighboring atomic sites on timescales less than 10 fs. The observation is made possible by the ability of ultrafast high harmonic pulses to simultaneously and independently probe the magnetic state at two atomic sites, Co and Mn, during laser excitation. We find that the magnetization of Co is enhanced by the laser pulse, while that of Mn rapidly quenches. By comparing our measurements to density functional theory, we show that the optical excitation directly transfers spin from one magnetic sub-lattice to another, via preferred spin-polarized excitation pathways. The enhancement of ferromagnetic order demonstrates direct manipulation of spins via light, thus providing a path towards spintronic devices such as switches that can operate on few femtosecond or faster timescales.