All Optical Switching in TbFeCo Films

To push all-optical recording towards application and to understand the fundamental mechanism of all-optically induced magnetization switching, I report here on the ultimate time scales of the magnetic order quenching and re-orienting in magnetically hard TbFeCo films induced by circularly polarized femtosecond laser pulses via the inverse Faraday effect. A femtosecond time domain study of the magnetization switching induced by circularly polarized femtosecond laser pulses in magnetically hard TbFeCo films will be presented. The all-optically induced magnetization switching has been found to be triggered within 240 fs, following immediately the quenching of magnetic order at 160 fs, and a new magnetization direction is defined in 460 fs, the fastest magnetic writing event ever observed, achieving a new regime of the magnetization reversal time scale for spin based technologies.  Combined with the simulations based on a single macro-spin model, we have demonstrated a novel linear reversal mechanism in contrast to the conventional spin precession in the all-optically induced magnetization switching.

Dr Yongbing Xu
Department of Electronics, The University of York, UK

Hybrid Spintronic Materials and Devices

The major challenges for the development of the second generation spintronics capable of controlling both spin and charge are the integration of the magnetic and semiconductor materials and switching locally the magnetic elements by current. In this invited talk, we will first present the growth, interface magnetism and magneto-transport of several important magnetic/semiconductor hybrid spintronic structures, in particular, with half metallic magnetic oxides and Heusler alloys. The hybrid spintronic structures integrating half-metallic magnetic oxides and Heusler alloys are particularly exciting for the second generation spintronics as a 100% spin polarisation is expected for high efficient spin injection. We have synthesized for the first time single crystal half metallic Fe3O4 on GaAs, and further found a moderate Schottky barrier in this system ideal for spin-injection. Using the elementary specific XMCD technique, we have found that the reduced spin moments of the Heusler alloy films on GaAs come from the Mn rather than the Co, but the orbital moments are not reduced. In the metal based system, our XMCD study demonstrated that the Fe atoms on GaAs (100) are ferromagnetic with bulk-like spin moments down to nanometer and atomic scale. For device applications, we have fabricated a novel vertical magnetic/semiconductor spintronic device with a GaAs membrane, and a large change of MR was observed which indicates a large room temperature electric spin injection and detection in the hybrid spintronic structures. Along with the development of materials, we have also carried out detailed experimental investigation of current induced switching and electron transport measurements in patterned magnetic nanowires. We have shown the interplay between the current induced switching and magnetic fields in patterned nanowires. With focused MOKE and XPEEM, we have further detected directly the direction of the domain wall movement under both current and magnetic fields

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