Femtosecond switching and reading of magnetic vortex memory devices

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Our modern networked society keeps asking for smaller and faster memory devices, which are currently limited to GHz reading and writing speed (STT-MRAM). One way to reach the next stage, the THz regime, is using photonics. We present a magneto-optical concept that can provide both, proof of principle that the required magnetic switching works at THz frequencies, as well as understanding the processes with the required femtosecond temporal and nanoscale spatial resolution. The nanofabricated magnetic structure we will investigate for femtosecond magnetization switching is the magnetic vortex core of thin ferromagnetic discs. While magnetization circulates around this core, at its center the magnetization points either "up" or "down". Their size ~10 nm and perfect stability make them promising candidates for magnetic data storage devices operated at THz frequencies. Experimentally, we will follow simulations which have predicted that the magnetic field of a half-cycle MV/cm THz pulse could be used for femtosecond spin switching of these vortex cores. To combine this switching step with the required spatially localized reading step at the center of the vortex core, the THz pulse will be synchronized with a femtosecond X-ray pulse, focussed down to the nanoscale. This will enable to image the spin dynamics and thus the switching of magnetization at THz frequencies. To observe this magnetic switching at THz frequencies, we will use circularly polarized fs X-rays, applying a technique called X-ray magnetic circular dichroism (XMCD). By comparing the transmission between left and right circularly polarized pulses at specific absorption edges, one can retrieve the magnetization component normal to the plane of the vortex core. This project will enable the development of a disruptive magneto-optical technology that enables femtosecond switching and reading of magnetic vortex memory devices in collaboration with MPB Communications Inc. and few-cycle Inc., supported by international collaborators from Technion and Keio University, to scale the performance of the next generation of data storage devices.