Magnetic-Photoconductors: A Versatile Platform for Light Controlled Magnetism
by Bálint Náfrádi (EPFL Lausanne)
Tuesday, january 4th, 2018 from 13:00 to 14:00 (Europe/Budapest)
at KFKI camous Bldg 1. 2nd floor, Conference Room
Budapest, Konkoly Thege Miklos ut 29-33
Magnetic properties of matter, like dia-, para- or ferromagnetism, originate from the intrinsic spin and orbital freedom of electrons and are fixed by the interactions between electrons. The resulting magnetism finds numerous practical applications and, without a doubt, constitutes one of the foundations of our modern technology-based society. The "wired in" nature of magnetism, however, limits many applications. Rapid, reversible, energy-efficient magnetic switching is expected to lead to novel, disruptive technologies. Effective control of magnetism is feasible by strong magnetic fields and by change of temperature. However, the generation of locally-focused strong magnetic fields and its changing is a challenging task and not energy-efficient. Similarly, changing temperature also suffers from serious limitations.
The demand for rapid, reversible, energy-efficient magnetic switching by non-magnetic means fuels continuous research for energy-efficient manipulation of magnetism at smaller and smaller length scales. Despite of an intrinsically weak coupling between light and magnetism, light-control of magnetic phenomena is one of the most attractive methods due to the ease and speed to move or switch illumination.
Here, we report a novel approach to conquer in situ light-control of magnetism. [1,2] In brief, the principal concept to overcome the limitation of mutual restrictions of magnetic- and light-responsive systems is an appropriate design of heterostructures and complex nanoscale materials. The individual components exhibit the required uncompromised light sensitivity and magnetic properties. The light-control on magnetism comes from photo-electron diffusion between the light sensitive and magnetic components driven by chemical potential mismatch at the interface. Diffusion of charges generated in light sensitive material efficiently changes the magnetism of the nanosized components included in the nanostructure. This is an effective avenue at nanoscale because the photo-electron diffusion length is larger than the size of the nanoparticles.
 B. Náfrádi, P. Szirmai, M. Spina, H. Lee, O. V. Yazyev, A. Arakcheeva, D. Chernyshov, M. Gibert, L. Forró and E. Horváth, "Optically switched magnetism in photovoltaic perovskite CH3NH3(Mn:Pb)I3", Nature Communications, 7, 13406, (2016)
 B. Náfrádi, P. Szirmai, M. Spina, A. Pisoni, X. Mettan, N.M. Nemes, L. Forró and E. Horváth, "Tuning Ferromagnetism at Room Temperature by Visible Light", submitted