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Magnetic wave-guides

Magnetic wave-guides. Frédéric OTT, Sergey Khozevnikov Laboratoire Léon Brillouin CEA Saclay. Objectives. Study magnetic neutron wave-guides Neutron interaction with a modulated optical magnetic potential Coupling of both devices. Outline. Magnetic wave-guides Fabrication

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Magnetic wave-guides

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  1. Magnetic wave-guides Frédéric OTT, Sergey Khozevnikov Laboratoire Léon Brillouin CEA Saclay

  2. Objectives • Study magnetic neutron wave-guides • Neutron interaction with a modulated optical magnetic potential • Coupling of both devices

  3. Outline • Magnetic wave-guides • Fabrication • Characterization • Modelling • Future experiments • Direct observation of guided modes • Observation of GH effects in wave-guides • Modulated magnetization

  4. Magnetic wave-guides

  5. Magnetic neutron wave guides Optical index Soft magnetic layer Guiding layer (with low optical index) Pinned magnetic layer substrate

  6. Samples • Metallic systems : • Cu(10-20nm) / Al(50-80nm) / Cu(50nm) // glass • Py(10-20nm) / Ti(50-80nm) / Py(50nm) // glass • Produced by • evaporation (non magnetic systems) • sputtering (magnetic systems)

  7. X-rays characterization of a wave-guide structure • Guided mode signature : • presence of absorption “resonances” in the specular reflectivity signal reflectivity

  8. Neutron wave-guides • No absorption • BUT off-specular scattering absorption can be observed if there is any roughness • The off-specular signal is enhanced by the wave-guide structure

  9. ToF characterization of wave-guides

  10. Off-specular scattering on HADAS • Measurement Modelling

  11. Modelling wave-function propagation in wave-guides

  12. Modelling of neutron wave-guides • SimulReflec (available at http://www-llb.cea.fr/prism/programs/simulreflec/simulreflec.html Theta in z Cu Al Cu Air Cu Ti Cu Air Cu Al Cu Air (75nm) (50nm) (75nm)

  13. WG optimization • The potential well should not be too deep • Al is perfectly suitable for the guide material • Ti provides a contrast which is too largeThe first mode cannot be confined in the guide • The use of Al make the structures easy to test with x-rays

  14. Wave-packets • It is necessary to take into account the wave-packet propagation • Goos - Hanchen effect • This has been included in « SimulReflec »

  15. Goos – Hanchen effect • Direct observation of the Goos –Hanchen shift • The Goos-Hanchen effect is multiplied by the wave-guide structure Ignatovitch et al, PLA 322 (2004)

  16. Modelling : to be done • Wave-packet in polarized mode • The interaction with a dynamically modulated magnetization must be included • There is significant off-specular scattering from the wave-guide structures • The full model ends up being quite complicated

  17. Dynamic magnetization modulation

  18. Modulated Magnetic Potential • Use of a magnetic modulation to dynamically vary the optical properties of a reflecting layer. • Principle : • Magnetisation of the layer rotates at speed w • Optical potential : V(t) = U + u(t) Optical index Potential variations due to the rotation of the magnetisation Vacuum (incidence medium) Magnetic layer

  19. Principle • Change of momentum of the neutron when there is an exchange of a quantum (during a spin-flip). • Amount of “inelastic reflection” in grazing incidence (around de 0.5°) • a large fraction of the incident beam (between 10 and 30%) . • [1] A. Frank et al, Ann. Of the New York Ac. Sc. 755 (1995) 858.[2] R. Golub et al, Am. J. Phys. 62 (1994) 779. Incident beam specular reflection (NSF) « inelastic » reflection (SF)

  20. Potential applications • Control of the reflection angles and reflection by varying the frequency • Coherent separation of a beam (for interferometry) • Wavelength dispersion for a time of flight reflectometer for an energy analysis of a white beam. • Neutron switch in the case of a magnetic pulse • Solid flipper with tunable parameters.

  21. Combination : dynamics and wave-guides • Magnetic traps Allows the neutron beam to freely enter the guide Acts like a guide

  22. Combination : dynamics and wave-guides • The modulation of the top magnetic layer should allow to trap neutron bunches inside the waveguide

  23. Modulated Magnetic Potential • Objective : • Modulate the magnetization of the layer in the WG • A new Kerr effect set-up has been built • Use for “off-line” characterization of the samples • Operates in “static mode” • Does not yet operate in RF mode(sensitivity issues) • Magnetic wave-guides will be patterned to avoid electrical losses (U.V. lithography)

  24. Conclusion • Planned experiments • Direct observation of the guided modes • Direct observation of the GH shift(in collaboration with University of Rennes) • Wave-guide structures are quite complicated systems • They offer a wealth of possible studies

  25. EN STOCK

  26. Samples • Large magnetisation • Low coercivity (Amorphous layers) • Permalloy – Co alloys • Single crystal layers • Low damping (Fe, a = 0.005) • Problem of the losses in the system • Insulating ferromagnets (magnetic oxides) • Patterned layers

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