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Quantum Mechanics and Spin-Valves Thomas Prevenslik QED Radiations Discovery Bay, Hong Kong The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing,

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Presentation on theme: "Quantum Mechanics and Spin-Valves Thomas Prevenslik QED Radiations Discovery Bay, Hong Kong The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing,"— Presentation transcript:

1 Quantum Mechanics and Spin-Valves Thomas Prevenslik QED Radiations Discovery Bay, Hong Kong The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China

2 Spin-Valve ferromagnetism is based on theoretical predictions by Slonczewski and Berger a decade ago. SpinValves comprise alternating nanoscale layers of FMs separated by a NM spacer. Spin-polarized current is produced by passing un-polarized current through a first FM layer, the polarization unchanged as the current flows through the NM spacer. In the second FM layer, a giant magneto-resistance (GMR) is thought to transfer the spins, the process tending to produce parallel spins that significantly lower the GMR. Note: 2007 Nobel prize awarded in spin reduction of GMR Introduction 2 The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China 2013

3 Unresolved Issues The significant reduction in the GMR by the alignment of spins is controversial  Holes alone are the mechanism Spin alignment by current, but is magnetic field required?. The relatively rigid lattice shields the spins so that any transfer of spin-torque to the second FM is questionable. Spin-torque propagates by phonons through the FM lattices, that limits spin-transfer response times > 100 ps. However, electron spins observed to respond much faster. The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China

4 Laser studies in femtomagnetism by Boeglin et al. show nanoscale FMs demagnetize on a sub-picosecond time scale Bigot et al. showed about 10 ps for the lattice to thermalize before which phonons cannot respond Bovensiepen noted* the dynamics are only observed while the laser field interacts with the FM Similarity with the momentary EM confinement of a MDR quasi-bound state, trapped in a potential well, but leaking to the outside world by tunneling. Proposed GMR mechanism is QED radiation created from Joule heat upon momentary TIR confinement of the atom QED = quantum electrodynamics TIR total internal reflection Alternative The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China

5 Provided the RI of the FM is greater than that of the adjacent NM spacers, non-thermal EM radiation at EUV levels is created by the QED induced frequency up-conversion of Joule heat to the TIR confinement frequency of the FM. Excitons (holon and electron pairs) are readily created by QED induced radiation. Holons (positive charges) act as carriers that significantly reduce the GMR of the FM by an increase in conductivity induced by QED QED Induced Conductivity The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China

6 Theory Heat Capacity of the Atom Conservation of Energy TIR Confinement 6

7 Heat Capacity of the Atom 7 Nano FMs kT eV Classical Physics (kT > 0) QM (kT = 0) The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China 2013 In nanoscale FMs, QM requires atoms to have zero heat capacity

8 The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China 2013 Conservation of Energy Lack of heat capacity by QM precludes Joule heat conservation in nanoscale FMs by an increase in temperature, but how does conservation proceed? Proposal Absorbed EM energy is conserved by creating QED induced excitons inside the FM layer by frequency up - conversion to the TIR resonance. 8

9 Since the RI of Spin-valves > surroundings, the Joule heat is momentarily confined in the quasi-bound MDR state of the atom Nanostructures ( films, wires, NPs) have high surface to volume ratio, but why important? Dangling bonds  Magic of NPs? Proposal: The Joule heat absorbed in the NP surface creates QED radiation in TIR mode at EUV levels  Magic QED radiation is spontaneously created by Joule heat dissipated in nanoscale FMs. Equations are, f = (c/n) / and E = hf TIR Confinement 9 The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China 2013 For a FM having thickness d, = 2d

10 The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China 2013 Electrical Response QED Photons and Excitons Exciton Response Resistance and Current 10

11 Exciton Source and Loss The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China Exciton Source from Joule Heat P = Joule heat E = QED Photon energy  = Fraction of P absorbed in Element (1-  ) = Fraction of P loss to Surroundings Excitons / s Exciton Loss to Electrodes Q = Number of Excitons  = Mobility V = Voltage d = thickness Excitons / s

12 Exciton Response The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China 2013 Where, Q E and Q H are number electrons and holons, V is the voltage  E and  H are electron and holon mobility Electrons Holons 12 For SpinValves, Ovshinsky effect, and 1/f Noise, V =  V o, For memristors, V = V o sin  t.

13 Resistance and Current The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China  = Conductivity  = Resistivity

14 The QED induced switching is simulated for Alq3 film thicknesses of 10, 20, 50, and 100 nm. All films were assumed to have an initial GMR of R o = 1x10 6 ohms. A write voltage V o = +1 V for 10 ns followed by erase V o = -1 V for 10 ns The QED induced conductivity in GMR is significant The 10 nm film resistance ratio R/R o is reduced to ~ or (R ~ 624 ohms) in < 1 ns. In contrast, magnetic induced GMR reductions for 125 nm Alq3 film at 100 K shows a GMR reduction of about 22% corresponding to R/R o = 0.78 Simulation The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China

15 Resistance The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China 2013 GMR resistance change - Write and Read For +1 V write and -1 V erase cycle 15 Vo = + 1 VVo = -1 V

16 QED induced conductivity by holons causes GMR reduction GMR reductions by electron spin alignment are insignificant Unexpected Finding The 10 nm film resistance change predicted by the QED induced conductivity in Alq3 films suggests superconductivity already exists or at least may be approached at ambient temperature. Conclusions The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China

17 Questions & Papers The 13th IEEE Inter. Conf. on Nanotechnology, August 5-8, Beijing, China 2013


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