Physics Coral Gables, Florida 33124, USA

Transcription

1 Physics Coral Gables, Florida 33124, USA The Spin Battery

2 Spin Battery Spin battery S. E. Barnes and S. Maekawa Phys. Rev. Lett (2007)

3 Except for solar cells, the generation of electrical power invariably corresponds to the conversion of mechanical into electric energy. The basic physical principle involved is Faraday's law of induction. On the other hand, in a battery, energy is invariably stored in chemical form. When needed, energy is produced via reversible chemical reactions. Charging the battery runs the reaction in the opposite direction. An electrical current corresponds to a flow of electrons and in both, Faraday law generation and chemical storage, it is the electrical charge of an electron which is important.

4 Faraday s Law Michael Faraday

5 Faraday s Law Michael Faraday

6 Physics

7 Physics

8 Spintronics is a relatively new field and is the art of creating new electronic devices which use the other attribute of an electron, namely its spin. The current trust in this area is the development of STT-MRAM (spin-torque-transfer magneticrandom-access-memory). An electron in addition to having an elementary charge -e also constitutes a small magnetic dipole which corresponds to its spin. It is essentially this property of an electron which is responsible for the magnetism of all magnet materials starting with elemental magnets such as Ni or Fe. In a typical spintronics device electrons pass from one thin film magnet to another through a thin oxide barrier. The spintorque-transfer process reverses the direction of the magnetisation of one of these magnetic layers. If the layer in one direction is 0 this writes a 1 into memory.

9 Basics: Charge current in Free layer Small anisotropy energy Fixed layer Large anisotropy energy Charge current out Polarisation of charge current: ferromagnet Conduction electron polarisation p

10 Hitachi-Tohoku Univ. Jointly Prototype 2 Mbit Nonvolatile RAM Based on Spin Torque Transfer

11 Vector additions

12 Ralph-Stiles

13 Coulomb Blockade Single-Electronics Made Easy Single-electronics implies the possibility to control the movement and position of a single electron or a small number of electrons. It is interesting to see how strong an influence a single electron with the minute charge of C C. Consider an uncharged small metallic sphere with a radius of 1 nm, something quite possible being produced today. Fig. 1: An electron approaching a small uncharged metallic sphere will feel a small attractive force caused by its own image charge in the sphere. Once the sphere is charged by a single electron, following electrons will feel a strong repelling Coulomb force.

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15 Nano-magnets

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17 Which direction is the current? The Kondo surface.

18 Spin Battery Spin battery S. E. Barnes and S. Maekawa Phys. Rev. Lett (2007)

19 Working magnetic material Energy High energy state Spin Faraday - STT - process Electrical energy Low energy state Parameter

20 A single domain wall S. E. Barnes and S. Maekawa Phys. Rev. Lett (2007) Geoffrey S. D. Beach S. A. Yang, G. S. D. Beach, C. Knutson, D. Xiao, Q. Niu, M. Tsoi,and J. L. Erskine, Phys. Rev. Lett. 102, (2009). SU(2) gauge theory, the Berry phase and spintronics, TCM Cambridge, June

21 SU(2) gauge theory, the Berry phase and spintronics, TCM Cambridge, June

22 Spin battery A tale of many channels

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25 Working magnetic material Energy High energy state Spin Faraday - STT - process Electrical energy Low energy state Parameter

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29 10 4 J/kg - conservative 10 5 J/kg - optimistic 4.6 X10 5 J/kg - Li - ion

30 Theoretical Maximum If one changes the magnetic state it is possible to recover the Jsd~4eV exchange energy. This gives 4.0x10 6 J/kg

31 Direction: Develop theory for present and new devices. 1. Confirm emf for different nano-magnet system. 2. Vary parameters to check theory. 3. Develop theory and experiment for new materials. 4. Address the scale up possibilities. 5. Demonstration batteries.

32 Hitachi-Tohoku Univ. Jointly Prototype 2 Mbit Nonvolatile RAM Based on Spin Torque Transfer

33 Physics

34 Physics

35 + + + Es - - -

36 Es + Es

37 Es + Es

38 Es Es

39 Inverse blockade

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43 Magnetic behaviour

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