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-78457 Konstanz, Germany
3 - Zukunftskolleg, Universität Konstanz, D-78457 Konstanz, Germany
4 - Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain
Tuesday 31st March 2015
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, 205-208 (2011).
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Challenges
Size
Confinement
Ostler et al., Nature
Comms, 3, 666
(2012).
Heat
dissipation
Magnetic storage
Thermally
Induced
Switching
Application
s
Materials
Mechanism
Azim et al., IEEE
Electron Device
Letters, 35,
Issue 12, 13171319 (2014).
AFM
Exchange
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Composition
Optical
arxiv: 1409.1280
Energy
transfer
to
magnetic
interconnects
system
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Controlling energy transfer to the spin system
Kaganov et al., JETP 1957
Anisimov et al., JETP 1974
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Range of values of electron-phonon coupling
Max and min values
100
•
Order of magnitude range in
values.
•
Can be calculated from
electronic structure calculations
or fitted from reflectivity
measurements.
Ge− ph [×1017W/ m3K ]
Co/Pt
Koopmans
GdFeCo (simulations)
FePt
10
Fe alloys
FePt
1
Koopmans
0.1
Ni Co Fe Pt Gd Tb
Important consideration when looking for new materials
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References
Koopmans Nat Mat 9, 259-265 (2010)
Mendil Sci Rep 4, 3980 (2014)
Verstraete J.Phys: Cond Matt 25, 136001 (2013)
Ostler Nat Comm 3, 666 (2012)
Radu Nature 472, 205-208 (2011)
Radu PRL 91, 22 (2003)
Kimling PRB 90, 224408 (2014)
Koopmans Nat Mater (2009)
Caffrey Thermoscale Thermophys. Eng. 2005
Beaurepaire PRL 1996
Wellershof 1998 Proc. SPIE
Bovensiepen J. Phys.: Cond. Mat 19 083201 (2007)
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Magnetic model
•
Energetics based on the Heisenberg Hamiltonian combined with the stochastic LandauLifshitz-Gilbert equation. Heisenberg parameters fitted to experimental measurements
[1].
Damping
Precession
describes rate of
transfer of energy into
(below) and out of
(above) the system
Noise
Thermal effects
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[1] - Ostler et al. Phys Rev B 84, 024407 (2011)
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Composition Optimisation
Barker et al. Nature Scientific Reports, 3, 3262 (2013).
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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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The role of e-ph coupling on thermal switching
Switching favours high peak
temperatures and longer pulse
durations
(more heat to magnetic system)
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Damping and Summary
•
•
Attempts to incorporate the detailed
mechanism of energy transfer from
subsystems.
Extremely difficult to quantify the exact
mechanism.
Optimisation of
composition/thickness of
multilayers
Low e-p coupling gives
more efficient heating
effect
High thermal bath
coupling
More
efficient
switching
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Acknowledgements
•
Funding from the EU FP7 project FemtoSpin,
grant agreement no. 281043.
•
•
Zukunftskolleg Incoming FellowshipProgramme 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 coordinated by the Universities of Leeds
and Manchester.
Tuesday 31st March 2015
[1] - Barker et al. Scientific Reports, 3, 3262 (2013).
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