A flavor of Nanomagnetism and Spintronics (2) Olivier Fruchart - - PowerPoint PPT Presentation

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A flavor of Nanomagnetism and Spintronics (2) Olivier Fruchart Institut Nel (CNRS-UJF-INPG) Grenoble - France http://neel.cnrs.fr Institut Nel, Grenoble, France http://perso.neel.cnrs.fr/olivier.fruchart/slides/

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SLIDE 1

http://perso.neel.cnrs.fr/olivier.fruchart/slides/ http://perso.neel.cnrs.fr/olivier.fruchart/slides/

Institut Néel, Grenoble, France

A flavor of Nanomagnetism and Spintronics (2)

Olivier Fruchart

Institut Néel (CNRS-UJF-INPG) Grenoble - France

http://neel.cnrs.fr

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SLIDE 2

Olivier Fruchart – Meeting – Place.Date – p.2

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

SPINTRONICS ToC →

  • 1. Magnetoresistance
  • 2. Spin transfer for magnetization switching
  • 3. Spin transfer for domain wall motion
  • 4. Other simuli : electric field, light, temperature etc.
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SLIDE 3

Olivier Fruchart – Meeting – Place.Date – p.3

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

Principle of GMR MAGNETORESISTANCE – Giant magnetoresistance

Two-current model E d d s s Fermi level

Features

Geometry: multilayers Magnitude: ≤ 40-50%

) cos(θ

∝ ∆ R

Applications

  • Magnetic sensors:

compass, read heads

  • Magnetic memory direct reading

Discovery: 1988, groups of A. Fert (CNRS-Thalès) and P. Grünberg (Jülich) Ferro1 Ferro2 Metal

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SLIDE 4

Olivier Fruchart – Meeting – Place.Date – p.4

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

MAGNETORESISTANCE – Tunneling magnetoresistance Principle of TMR

  • Electron tunnelling between electrodes

Ferro1 Ferro2 Insulator

w E eV E0

  • Classical machanics: no current
  • Quantum mechanics: tunneling current

ψ ψ ψ

E x V dx d m

= + −

) ( 2

2 2 2

Schrödinger’s equation:

Discovery: 1975 (Jullière); ‘rehabilitated’ 1995, Moodera et coll.

E d d s s Fermi level

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SLIDE 5

Olivier Fruchart – Meeting – Place.Date – p.5

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

MAGNETORESISTANCE – Tunneling magnetoresistance Features

Geometry: multilayers Magnitude: up to 400% at RT High resistance Ultrathin oxyde layer

) cos(θ

∝ ∆ R

Applications

  • Direct reading of memory cells
  • Magnetic field sensors
  • Reprogrammable magnetic logic
  • S. Yuasa et al., Appl. Phys. Lett. 89, 042506 (2006)

Beyond Jullière's model

Spin filtering in textured Mg(001)

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SLIDE 6

Olivier Fruchart – Meeting – Place.Date – p.6

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

MAGNETORESISTANCE – Evolution in HDD heads

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SLIDE 7

Olivier Fruchart – Meeting – Place.Date – p.7

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

SPINTRONICS ToC →

  • 1. Magnetoresistance
  • 2. Spin transfer for magnetization switching
  • 3. Spin transfer for domain wall motion
  • 4. Other simuli : electric field, light, temperature etc.
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SLIDE 8

Olivier Fruchart – Meeting – Place.Date – p.8

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

SPIN TRANSFER – Switching

'Polarizer' 'Free layer'

Spin transfer effect

Can be viewed as the GMR-reversed effect

  • J. C. Slonczewski (1996)
  • L. Berger (1996)

Electron flow – Carrying magnetic moment u=(P gμB/2e M S) j

Example

Myers & Ralph, Cornell (2000)

Field switching Current switching

Simplified architectures for writting bits (MRAMs etc.) Fully electronic read/write Devices with domain wall motion (memory, logic) Devices for GHz oscillators

Motivations

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SLIDE 9

Olivier Fruchart – Meeting – Place.Date – p.9

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

SPIN TRANSFER – Switching

Field-like (preserves energy)

˙ m=γ0(H+b I mp)×m+α m× ˙ m−γa I m×[m×mp]

Spin-transfer (brings or removes energy)

  • S. I. Kiselev, Nature 425, 380 (2003)

Physics : torques and precession Switching and oscillators

u=(P gμB/2e M S) j a and b depend on

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SLIDE 10

Olivier Fruchart – Meeting – Place.Date – p.10

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

SPINTRONICS ToC →

  • 1. Magnetoresistance
  • 2. Spin transfer for magnetization switching
  • 3. Spin transfer for domain wall motion
  • 4. Other simuli : electric field, light, temperature etc.
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SLIDE 11

Olivier Fruchart – Meeting – Place.Date – p.11

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

Magnetic logic with domain walls (Field driven) SPIN TRANSFER – Domain wall motion – Motivation

  • D. A. Allwood et al., Science 309, 1688 (2005)

Magnetic memories with domain walls (Current driven) Limitation: Requires homogeneous rotating field Makes use of spin transfer effect Potentially 3D storage, however technologically challenging

  • S. S. P. Parkin, IBM-Almaden

U.S. patents 6834005, 6898132, 6920062

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SLIDE 12

Olivier Fruchart – Meeting – Place.Date – p.12

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

non-adiabatic adiabatic precession damping

Zhang and Li, PRL 93, 127204 (2004) Thiaville et al., EPL 69, 990 (2005) Tatara et al., JPSJ 75, 064708 (2006)

Landau Lifshitz Gilbert equation + two “spin transfer torque” terms

SPIN TRANSFER – Domain wall motion – Precessional physics Modified Landau-Lifshitz equation Fundamental physics: origin and magnitude of β unclear Experimental determination of β necessary Stripes and wires are different

Flow of magnetic moment:

˙ m=γ0H×m+α m× ˙ m−(u.∇)m+βm×[(u. ∇)m]

u=(P gμB/2e M S) j

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SLIDE 13

Olivier Fruchart – Meeting – Place.Date – p.13

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

SPIN TRANSFER – Domain wall motion – Reminder : what domain walls look like

2 μm 200nm

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SLIDE 14

Olivier Fruchart – Meeting – Place.Date – p.14

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

SPIN TRANSFER – Domain wall motion – Mobility

  • G. S. D. Beach et al., Nature. Mater. 4, 741 (2005)
  • A. Thiaville et al., Europhys. Lett. 69, 990 (2005)

Propagation in field Propagation in current

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SLIDE 15

Olivier Fruchart – Meeting – Place.Date – p.15

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides 0.0 1.0 2.0 3.0 4.0 5.0 100 200 300 400

Mean v Linear fit

DW velocity (m/s) Current density (x 10

12 A/m 2)

10 µm

DWs prepared by field pulses Domain nucleation pad

Au/Ti contact pad Au/Ti contact pad 500 nm SPIN TRANSFER – Domain wall motion – Rashba effect Pt(3nm) / Co(0.6nm) / AlOx(2nm) Measuring device

  • T. A. Moore et al., Appl. Phys. Lett. 93, 262504 (2008)
  • M. Miron, Nature. Phys. 9, 230 (2010)

Results First, non-linear regime (DW creep) Second, linear regime (flow) High DW mobility Rashba-like effect for high β ?

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SLIDE 16

Olivier Fruchart – Meeting – Place.Date – p.16

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

SPINTRONICS ToC →

  • 1. Magnetoresistance
  • 2. Spin transfer for magnetization switching
  • 3. Spin transfer for domain wall motion
  • 4. Other simuli : electric field, light, temperature etc.
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SLIDE 17

Olivier Fruchart – Meeting – Place.Date – p.17

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

OTHER STIMULI – Electrical field

  • M. Weisheit et al., Science 315, 349 (2007)

Electric modification of intrinsic properties

See also: magnetic semiconductors, multiferroics etc. See follow-up : reversal with electric field :

  • T. Nozaki et al., Appl. Phys. Lett. 96022506, (2010).
  • M. Weiler et al., New J. Phys. 11, 013021 (2009)
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SLIDE 18

Olivier Fruchart – Meeting – Place.Date – p.18

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

OTHER STIMULI – Electrical field

Gd22Fe74.6Co3.4

  • C. D. Stanciu et al.,
  • Phys. Rev. Lett. 99, 047601 (2007)

Principle

Combined heating + inverse Faraday effect Magneto-optical

  • material. Tc=500K

Preliminary: one shot with large power

Demagnetized Magnetization reversed

Local reversal with controlled power

Ti:S laser: =800nm; =40fs.

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SLIDE 19

Olivier Fruchart – Meeting – Place.Date – p.19

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

OTHER STIMULI – Temperature

  • K. Uchida et al., Nature 455, 778 (2008)

Similar to thermoelectricity, however with spin-dependant chemical potential

Spin Seebeck

coefficient

Generation of pure spin

currents

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SLIDE 20

Olivier Fruchart – Meeting – Place.Date – p.20

Institut Néel, Grenoble, France

http://perso.neel.cnrs.fr/olivier.fruchart/slides

Thank you and bye-bye !