"Interplay of structure and magnetism during ultrafast optical excitations"

Who: Eric Fullerton, UC San Diego, USA

Place: nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian

Date: Friday, 20 April 2018, 15:00

The possibilities of optically manipulating magnetization without applied magnetic fields have attracted growing attention over the last fifteen years. The low-power manipulation of magnetization, preferably at ultra-short time scales, has become a fundamental challenge with implications for future magnetic information memory and storage technologies [1]. There are further opportunities for structural control at fs time scales via the magneto-structural interaction. I will discuss two systems where ultrafast optically-induced demagnetization drives structural dynamics. The first systems is FePt-based granular media [2, 3] designed for next generation magnetic recording. We find that optical magnetic switching by circularly polarized light is an accumulative effect from multiple optical pulses [3]. Following the excitation of FePt granular film with a 50-fs laser pulse, time-resolved X-ray magnetic diffraction demonstrates that magnetic order is lost with a characteristic time constant of 146 fs. Ultrafast electron diffraction measurements reveal that this demagnetization is followed by a highly anisotropic, three-dimensional lattice motion. The size, speed and symmetry of the observed lattice motion reveal the magneto-elastic stress, which is generated by the sudden disordering of magnetization. The second systems we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the magnetically stabilized charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. 

1) Hellman et al. Rev. Mod. Phys. 89, 025006 (2017) 
2) Lambert et al., Science 345, 1337-1340 (2014). 
3) Takahashi et al. Phys. Rev. Appl. 6, 054004 (2016). 
4) A. H. Reid et al., Nature Comm. 9, 388 (2018). 
5) A. Singer et al., Phys. Rev. Lett. 117, 056401 (2016) 

Dr. Fullerton is an internationally acclaimed scholar in areas such as thin film and superlattice growth, magnetic recording and nano-technologies, and x-ray and neutron scattering. At IBM/Hitachi, Dr. Fullerton made fundamental advances in the development of high density magnetic recording media based on anti-ferromagnetically coupled ferromagnetic films. Early in his career, he developed a technique for mapping the structure of thin-film multi-layers from x-ray diffraction data that became the standard in the field.

 Host: A. Berger

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