Ultrafast enhancement of magnetization in ferromagnetic semiconductor (In,Fe)As quantum wells*

Controlling the magnetization of ferromagnets on a subpicosecond (sub-ps) time scale is highly desirable, although challenging, for ultrafast spin-based electronics. Thus far, control the magnetic properties of a ferromagnetic materials usually requires changing a large amount of carriers of the ferromagnet, which leads to large power consumption and slow operation speed. Here we demonstrate for the first time sub-ps enhancement of ferromagnetism only by moving wavefunctions (WF) in ferromagnetic semiconductor (In,Fe)As/InAs bilayer quantum wells (QWs). We conducted pump-and-probe measurements, using a fs-pulse laser (wavelength 793 nm) as the pump source and an X-ray free electron laser (XFEL) beam with energy of 52 eV as the probe. Upon irradiating the pumping laser, we observe an extremely fast enhancement, corresponding to 600 fs, of the magnetization of the (In,Fe)As QW. Our analysis shows that the 2-dimensional electron WF in the FMS QW is rapidly moved by a photo-Dember electric field, which induces the instant magnetization enhancement [1]. This new method for sub-ps magnetization control is compatible with CMOS technology, thus opens a new way to ultrafast magnetic storage and information processing.