Ultra-fast Creation and Destruction of Ferromagnetic nanowires

The field of nano-spintronics aims to deliver novel multi-functional devices by manipulating magnetism on unprecedented length and time scales. Here we present a technique for ultra-fast creation and destruction of ferromagnetic nanowires at room temperature. We focus on MnAs films where ferromagnetic nanowires are observed within $\pm20$ degrees of room temperature. The existence of the nanowires is monitored via Terahertz Time Domain spectroscopy (THz-TDS) through the anisotropic transmission that they induce. Upon optical excitation, the ferromagnetic nanowires are either created or destroyed, depending on the temperature and history of the sample. Thus we provide a new method for the detection and manipulation of magnetism on the nanoscale.