Presentation on theme: "Energy Efficient Thermally Induced Switching by Tailoring the Electron and Phonon Dynamics T. Ostler 1, U. Atxitia 2,3, O. Chubykalo-Fesenko 4 and R.W."— Presentation transcript:
Energy Efficient Thermally Induced Switching by Tailoring the Electron and Phonon Dynamics T. Ostler 1, U. Atxitia 2,3, O. Chubykalo-Fesenko 4 and R.W. Chantrell Dept. of Physics, The University of York, York, United Kingdom. 2 - Fachbereich Physik, Universität Konstanz, D Konstanz, Germany 3 - Zukunftskolleg, Universität Konstanz, D Konstanz, Germany 4 - Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, Madrid, Spain Tuesday 31 st March 2015
Background: Thermally Induced Magnetization Switching Single linearly polarised femtosecond laser pulse. Linearly polarised = no induced magnetism from E-field (inverse Faraday effect). Ostler et al., Nature Comms, 3, 666 (2012). (left) Time and element resolved dynamics (XMCD). Switching complete after <2ps. Material: Amorphous Ferrimagnetic GdFeCo Radu et al., Nature, 472, (2011). Tuesday 31 st March 20152/11
Challenges Thermally Induced Switching Application s Mechanism Materials AFM Exchange Energy transfer to magnetic system Composition Confinement Heat dissipation Azim et al., IEEE Electron Device Letters, 35, Issue 12, (2014). Optical interconnects Magnetic storage Ostler et al., Nature Comms, 3, 666 (2012). Size Tuesday 31 st March 20153/11 arxiv:
Controlling energy transfer to the spin system Tuesday 31 st March 20154/11 Kaganov et al., JETP 1957 Anisimov et al., JETP 1974
Range of values of electron-phonon coupling Tuesday 31 st March 20155/11 Max and min values Order of magnitude range in values. Can be calculated from electronic structure calculations or fitted from reflectivity measurements. References Koopmans Nat Mat 9, (2010) Mendil Sci Rep 4, 3980 (2014) Verstraete J.Phys: Cond Matt 25, (2013) Ostler Nat Comm 3, 666 (2012) Radu Nature 472, (2011) Radu PRL 91, 22 (2003) Kimling PRB 90, (2014) Koopmans Nat Mater (2009) Caffrey Thermoscale Thermophys. Eng Beaurepaire PRL 1996 Wellershof 1998 Proc. SPIE Bovensiepen J. Phys.: Cond. Mat (2007) Important consideration when looking for new materials
Magnetic model Tuesday 31 st March 20156/11 Energetics based on the Heisenberg Hamiltonian combined with the stochastic Landau- Lifshitz-Gilbert equation. Heisenberg parameters fitted to experimental measurements . Thermal effects  - Ostler et al. Phys Rev B 84, (2011) describes rate of transfer of energy into (below) and out of (above) the system
Composition Optimisation Tuesday 31 st March 20157/11 Barker et al. Nature Scientific Reports, 3, 3262 (2013).
Mechanism for Switching – requirement for AFM exchange Tuesday 31 st March 20158/11 Overlapping bands allows for efficient transfer of energy. Large band gap precludes efficient energy transfer. Barker et al. Nature Scientific Reports, 3, 3262 (2013). Data shown 25% (switches) and 35% (does not switch) Gd, both ferrimagnetic.
The role of e-ph coupling on thermal switching Tuesday 31 st March 20159/11 Co based alloys Fe/Ni based alloys Gd/Tb Switching favours high peak temperatures and longer pulse durations (more heat to magnetic system)
Damping and Summary Tuesday 31 st March /11 Attempts to incorporate the detailed mechanism of energy transfer from subsystems. Extremely difficult to quantify the exact mechanism. More efficient switching Low e-p coupling gives more efficient heating effect Optimisation of composition/thickness of multilayers High thermal bath coupling
Acknowledgements Tuesday 31 st March /11  - Barker et al. Scientific Reports, 3, 3262 (2013). Funding from the EU FP7 project FemtoSpin, grant agreement no Zukunftskolleg Incoming Fellowship- Programme Marie Curie (ZIF-MC). This work made use of the facilities of N8 HPC provided and funded by the N8 consortium and EPSRC (Grant No.EP/K000225/1). The Centre is co- ordinated by the Universities of Leeds and Manchester.