1. Energy Efficient Thermally Induced Switching by Tailoring the Electron and Phonon Dynamics
T. Ostler1, U. Atxitia2,3, O. Chubykalo-Fesenko4 and R.W. Chantrell1
1 - 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 31st March 2015

2. Material: Amorphous Ferrimagnetic GdFeCo
Background: Thermally Induced Magnetization Switching
Single linearly polarised femtosecond laser pulse.
Linearly polarised = no induced magnetism from E-field (inverse Faraday effect).
Material: Amorphous Ferrimagnetic GdFeCo
Ostler et al., Nature Comms, 3, 666 (2012).
(left) Time and element resolved dynamics (XMCD).
Switching complete after <2ps.
Radu et al., Nature, 472, (2011).
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3. Challenges Magnetic storage arxiv: 1409.1280 Optical interconnects
Size
Confinement
Ostler et al., Nature Comms, 3, 666 (2012).
Heat dissipation
Thermally Induced Switching
Applications
Magnetic storage
Materials
Mechanism
Azim et al., IEEE Electron Device Letters, 35, Issue 12, (2014).
arxiv:
AFM Exchange
Composition
Energy transfer to magnetic system
Optical interconnects
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4. Controlling energy transfer to the spin system
Kaganov et al., JETP 1957
Anisimov et al., JETP 1974
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5. Range of values of electron-phonon coupling
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. 2005
Beaurepaire PRL 1996
Wellershof 1998 Proc. SPIE
Bovensiepen J. Phys.: Cond. Mat (2007)
Important consideration when looking for new materials
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6. [1] - Ostler et al. Phys Rev B 84, 024407 (2011)
Magnetic model
Energetics based on the Heisenberg Hamiltonian combined with the stochastic Landau-Lifshitz-Gilbert equation. Heisenberg parameters fitted to experimental measurements [1].
describes rate of transfer of energy into (below) and out of (above) the system
Thermal effects
Tuesday 31st March 2015
[1] - Ostler et al. Phys Rev B 84, (2011)
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7. Composition Optimisation
Barker et al. Nature Scientific Reports, 3, 3262 (2013).
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8. Mechanism for Switching – requirement for AFM exchange
Data shown 25% (switches) and 35% (does not switch) Gd, both ferrimagnetic.
Overlapping bands allows for efficient transfer of energy.
Large band gap precludes efficient energy transfer.
Barker et al. Nature Scientific Reports, 3, 3262 (2013).
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9. The role of e-ph coupling on thermal switching
Co based alloys
Fe/Ni based alloys
Gd/Tb
Switching favours high peak temperatures and longer pulse durations
(more heat to magnetic system)
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10. Damping and Summary
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
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11. [1] - Barker et al. Scientific Reports, 3, 3262 (2013).
Acknowledgements
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.
Tuesday 31st March 2015
[1] - Barker et al. Scientific Reports, 3, 3262 (2013).
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