Light-induced magnetism in plasmonic gold nanoparticles

Strategies for the ultrafast optical control of magnetism have been a topic of intense research for several decades because of the potential impact in technologies such as magnetic memory(1), spintronics(2) and quantum computation, as well as the opportunities for nonlinear optical control and modulation(3) in applications such as optical isolation and non-reciprocity(4). Here we report experimental quantification of optically induced magnetization in plasmonic gold nanoparticles due to the inverse Faraday effect. The induced magnetic moment is large under typical ultrafast pulse excitation (<10(14) W m(-2) peak intensity), with magnetization and demagnetization kinetics that are instantaneous within the subpicosecond time resolution of our study. Our results support a mechanism of coherent transfer of angular momentum from the optical field to the electron gas, and open the door to all-optical subwavelength strategies for optical isolation that do not require externally applied magnetic fields. Optically induced magnetization is experimentally demonstrated using gold nanoparticles. The inverse-Faraday-effect-enabled magnetization may lead to new types of compact optical isolator.