SUB-PICOSECOND CONTROL OF NANO-MAGNETS

The data storage capacity and the speed of operation of a modern laptop computer are orders of magnitude greater than those of the first computers that occupied several large rooms. To maintain the pace of progress, both the physical bit size and the data access time must be reduced even further. Under these circumstances, the nano-magnetic technology is becoming one of the strongest players in the multibillion dollar market for high speed miniature devices for data storage and processing.This constitutes the main practical motivation for the proposed research programme which has the overall aim of gaining an ever-faster control of nanoscale magnetic structures by means of sub-picosecond optical and magnetic pulses. This will require that several issues of fundamental importance be resolved, extending our knowledge and understanding of ultrafast nano-scale magnetic dynamics to a new level.The basic phenomenon exploited in the project is the Inverse Faraday Effect due to which circularly polarised optical pulses can generate sub-picosecond pulses of magnetic field (so called photo-magnetic field), which are orders of magnitude shorter than the fastest electrical and magnetic pulses produced electronically or in ultrafast photo-diodes. The pulsed photo-magnetic field due to optical pulses from an ultrafast laser will be used to manipulate the magnetisation either directly, by using the photo-magnetic field itself, or indirectly, by converting it into pulses of the Oersted magnetic field within a novel device called a Faraday Optical Transformer. The magnetisation precession excited in magnetic thin films and nanoscale elements will be then traced magneto-optically by measuring the change of polarisation acquired by a delayed optical pulse (a probe ) upon reflection from the pumped sample. The magnetisation dynamics will be studied and imaged in both small (spin waves) and large (180 degrees reversal) amplitude regimes. A combined action of multiple pulses of photo-magnetic, Oersted and / or microwave fields will be investigated and used to optimize magnetic switching characteristics.The proposed research falls within the EPSRC's Nano World (Magnetic materials), Quantum Realm (Interaction of Light and Matter), and Miniature Machines (Photonics and Optoelectronics) priority areas.