[PPT] - (Quelques) tendances et dfis du magntisme en dimensions rduites PowerPoint Presentation

SLIDE 1

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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(Quelques) tendances et défis du magnétisme en dimensions réduites Fondements et applications à l’électronique de spin

O.Fruchart

Laboratoire Louis Néel (CNRS-UJF-INPG) Grenoble

SLIDE 2

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.2

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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CNRS from mountains

SLIDE 3

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.3

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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Lab in mountains

Part of the lab (Winter) Part of the lab (Winter) Part of the lab (Summer) Part of the lab (Summer)

SLIDE 4

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.4

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Currents, magnetic fields and magnetization r I B π µ 2 =

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − × = µ r µ.r) ( 3 4

2 3

r r B π µ µ

Magnetization: A.m-1 Magnetic moment: A.m2

Oersted field Magnetic moment Magnetic material

SLIDE 6

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.6

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Hysteresis loops

Hext M

Manipulation of magnetic materials: Application of a magnetic field

H.M

Z

µ − = E

Zeeman energy: Spontaneous magnetization Ms Remanent magnetization Mr

Hext M

Losses

M H E d

ext

∫

= µ

Coercive field Hc

SLIDE 7

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.7

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Magnetically soft and hard magnetic materials Soft materials

Transformers Flux guides Magnetic shielding

Hard materials

Permanent magnets, motors Magnetic recording

Hext M

SLIDE 8

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.8

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Sources of magnetic energy

2 2 1 2 , 1 Ech

) ( . θ ∇ = − = A J E S S ) ( sin 2

mc

θ K E =

H M .

S Z

µ − = E

1 2

d S d

. 2 1 H M µ − = E

Zeeman energy (enthalpy) Magnetocrystalline anisotropy energy Dipolar energy Echange energy

Hext M

SLIDE 9

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.9

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Magnetic characteristic length scales Typical length scale: Bloch wall width λB

( )

θ θ

2 2

sin / K dx d A e + =

Exchange Anisotropy

J/m

3

J/m

Numerical values

K A/

B

π λ =

nm 3 2

B

− = λ nm 100

B ≥

λ

Hard Soft

SLIDE 10

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.10

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Magnetization patterns Bulk material

Nanomagnetism ~ mesoscopic magnetism

Co(1000) crystal – SEMPA

A. Hubert, Magnetic domains

Mesoscopic scale

Numerous and complex magnetic domains Small number of domains, simple shape

Microfabricated dots Kerr magnetic imaging

A. Hubert, Magnetic domains

Nanometric scale

Magnetic single-domain

R.P. Cowburn, J.Phys.D:Appl.Phys.33, R1 (2000)

Magnetic recording essentially makes use of single-domain particles

SLIDE 11

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.11

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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Principle of GMR INTRODUCTION TO MAGNETISM – Giant magnetoresistance D(E) E d d s s

Spin filtering in an heterostructure Fermi level

Two-current model

Features

Geometry: multilayers Magnitude: ≤ 40-50%

) cos(θ ∝ ∆R

Applications

Magnetic sensors: compass, read heads
Magnetic memory direct reading

Discovery: 1988, A. Fert (CNRS-Thalès) and P. Grünberg (Jülich)

SLIDE 12

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.12

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Tunnelling magnetoresistance Principle of TMR

Spin filtering in heterostructures
Electron tunnelling between electrodes

Ferro1 Ferro2 Insulator

w E eV E0

Mécanique classique: pas de courant
Mécanique quantique: courant tunnel

ψ ψ ψ E x V dx d m = + − ) ( 2

2 2 2

h

Équation de Schrödinger

Features

Geometry: multilayers Magnitude: ≤ 100-150% High resistance Ultrathin oxyde layer

) cos(θ ∝ ∆R

Applications

Magnetic sensors
Magnetic memory direct

reading

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

SLIDE 13

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.13

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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Media: granular and columnar INTRODUCTION TO MAGNETISM – Magnetic recording : hard disks (media)

Grain : 10 nm 200 nm

Co-rich Cr-rich

CoPtCrTaB Disk

40 nm

Large number of grains per bit

SLIDE 14

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.14

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Magnetic recording : hard disks (heads and density)

Substrate

MR

Shielding Shielding Disk (rotation 7000-10000 rpm) Coils

~100nm ~7-8nm

Read-write heads

60 70 80 90 100 110

Production Year

1E-3 1E-2 1E-1 1E+0 1E+1 1E+2 1E+3 1E+4 1E+5 1E+6

Areal Density Megabits/in2

HGST Disk Drive Products Industry Lab Demos HGST Disk Drives w/AFC Demos w/AFC

HGST Areal Density Perspective

1st MR Head 1st GMR Head

2000 10

60% CGR

Ultrastar 146Z10 Deskstar 180GXP

100% CGR

Corsair Deskstar 16GP Travelstar 30GN Microdrive II

1st AFC Media

Future Areal Density Progress Travelstar 80GN

Perpendicular Recording Superparamagnetic effect

10

5

104 103 102 106 10 1 10-1 10-2 10-3

25% CGR

IBM RAMAC (First Hard Disk Drive)

1st Thin Film Head

3375 35 Million X Increase

Increase of areal density

The Physics of Ultrahigh-density Magnetic Recording,

M. Plumer, J., van Ek, D. Weller,

Springer (2001)

SLIDE 15

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.15

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Magnetic recording : hard disks (superparamagnetism)

UP DOWN

~25kT

τ / ) ( t e t P − =

T k E e

B B /

τ τ =

Phenomenological model

Brown, Phys.Rev.130, 1677 (1963)

Probability for non-reversal Mean waiting time for reversal

s 10

9 −

≈ τ

) / ln( τ t T k E

B B = Energy barrier required to prevent

magnetization reversal during duration t Laboratory : t =1s Recording : t >>109s

K T k V

B B

/ 25 ≈ K T k V

B B

/ 60 40 − ≈

Formalism for thermal excitations

Anisotropy barrier EB~KV

Orders of magnitude Steady increase of anisotropy K for magnetic recording > Some drawbacks > Physical limits? Anisotropy barrier

SLIDE 16

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.16

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTRODUCTION TO MAGNETISM – Magnetic memories : MRAMs Overview

Current Current

Detail of a cell

MRAM = Magnetic Random Access Memory (Close to commercial products)

Main features: Solid state memory Non-volatile and fast Complex, expensive, issues of reproductibility

I1 I2

Spin valve ‘Bit’ ligne

‘digit’ ligne ‘word’ ligne

Flux guides Magn flux lines Conductor (Cu) Transistor

SLIDE 17

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.17

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTERFACE PHENOMENA – Interface anisotropy

L. Néel,
J. Phys. Radium 15,

15 (1954)

« Cette énergie de surface, de l’ordre de 0.1 à 1 erg/cm2, est susceptible de jouer un rôle important dans les propriétés des substances ferromagnétiques dispersées en éléments de dimensions inférieures à 100Å » « This surface energy, of the order of 0.1 to 1 erg/cm2, is liable to play a significant role in the properties of ferromagnetic materials spread in elements of dimensions smaller than 100Å » « Anisotropie magnétique superficielle et surstructures d'orientation »

« Superficial magnetic anisotropy and orientational superstructures »

Overview Breaking of symmetry for surface/interface atoms Correction to the magneto-crystalline energy Pair model of Néel:

Ks estimated from magneto-elastic constants
Does not depend on interface material
Yields order of magnitude only: correct value from experiments or calculations

... ) ( cos ) ( cos

4 2 S, 2 1 S, s

+ + = θ θ K K E

Surface anisotropy

SLIDE 19

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.19

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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Experimental approach: 1/t plot INTERFACE PHENOMENA – Interface anisotropy

S V tot

2 ) ( k t k t E + = t 2 ) (

S V

k k t e + =

U. Gradmann and J. Müller,
Phys. Status Solidi 27, 313 (1968)

Bulk t=2AL

Historical example: First hints for perpendicular anisotropy

L B

µ µ ξ α ∆ = 4 MAE

P. Bruno,

PRB39, 865 (1989)

MAE (Magnetic Anisotropy Energy), perturbation theory for 3d metals:

L

µ

does not rotate in 3d metals

> MAE reflects cost in ξ

Covers magnetocrystalline, magnetoelastic and surface anisotropy

Theory

Important aspect: In most cases surface and magnetoelastic anisotropies are mixed (1/t plots etc.)

C. Chappert and P. Bruno., JAP64, 5736 (1988)
W. A. Jesser et al., Phys. Stat. Sol. 19, 95 (1967)

SLIDE 20

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.20

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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Co/Pt INTERFACE PHENOMENA – Interface anisotropy

Results

Bulk: mL=0.14µB/at.
Surface: mL=0.31µB/at.
Bi-atomic wire: mL=0.37µB/at.
Mono-atomic wire: mL=0.68µB/at.
bi-atom: mL=0.78µB/at.
atom: mL=1.13µB/at.
A. Dallmeyer et al., Phys.Rev.B 61(8), R5153 (2000)
P. Gambardella et al., Science 300, 1130 (2003)
P. Gambardella et al., Nature 416, 301 (2002)

Engineering of anisotropy

Platinum Cobalt

S. Rusponi et al., Nature Mater. (2003)

SLIDE 21

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.21

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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COUPLING PHENOMENA – Dipolar energy

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − = ) . ).( . ( 3 . 4

2 1 2 2 1 3 1,2

r µ r µ µ µ r r π µ E

Mutual energy of two magnetic dipoles :

Basics of dipolar energy

1 2 r Notice: Decays like 1/r^3 May favor parallel or antiparallel alignment Long-ranged in bulk, however short-ranged in 2D:

Cte 1 ~ d 1 ~ d 2 1

2 3

+

∫∫ ∫∫

R r r r r r π

SLIDE 23

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.23

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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Stacked dots : orange-peel coupling COUPLING PHENOMENA – Dipolar energy (examples) Stacked dots : dipolar

In-plane magnetization Out-of-plane magnetization

Hint: An upper bound for the dipolar coupling is the self demagnetizing field

Probe with reflectivity

Notice: similar situation as for RKKY coupling

+ + + + +

+

+ + + +

In-plane magnetization Always parallel coupling Out-of-plane magnetization May be parallel or antiparallel

L. Néel, C. R. Acad. Sci. 255, 1676 (1962)
J. C. S. Kools et al., J. Appl. Phys. 85, 4466 (1999)
J. Moritz et al., Europhys. Lett. 65, 123 (2004)

(valid only for thick films) (valid for any films)

SLIDE 24

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.24

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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COUPLING PHENOMENA – Dipolar energy (examples) Array of dots

V. Repain et al., J. Appl. Phys. 95, 2614 (2004)

Patterned array of Pt/Co(0.5nm)/Pt dots with perpendicular anisotropy (50x50 microns, demagnetized state) Example of perpendicular magnetization

Probe with off-specular or scattering

SLIDE 25

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.25

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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COLLECTIVE PROPERTIES – Exploit order for magnetic scattering

Magnetic scattering on nanofabricated arrays of lines

Co/Pt(111) multilayers Informations about magnetic correlations are extracted from magnetic satellites

K. Chesnel et al., PRB66, 024435 (2002)

XMRS: X-ray Magnetic Resonant Scattering

SLIDE 26

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.26

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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COLLECTIVE PROPERTIES – Exploit order for magnetic scattering

Structural scattering on self-organized systems: GISAXS

q CCD

INTRA-ROW ORDER: SUPER-CRYSTAL

Thickness: 1 Å ; coverage: 25%

Λ 4π/Λ

O. Fruchart et al., Europhys. Lett. 63, 275 (2003)

Evidencing magnetic scattering is in principle possible, however:

Low temperature and weak signal
Distribution of properties may prevent ordering to occur

Co/Au(111) nanodots

SLIDE 27

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.27

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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AFM FM

Meiklejohn and Bean,

Phys. Rev. 102, 1413 (1956),
Phys. Rev. 105, 904, (1957)

FC ZFC µ0HE ≈ 0.2 T

Exchange bias

J. Nogués and Ivan K. Schuller
J. Magn. Magn. Mater. 192 (1999) 203

Exchange anisotropy—a review A E Berkowitz and K Takano

J. Magn. Magn. Mater. 200 (1999)

INTERFACE PHENOMENA – Ferromagnetic / Antiferromagnetic coupling Seminal studies

Oxidized Co nanoparticles

Field-cooled hysteresis loops: Shifted in field Increased coercivity Frustration can induce 90° coupling between layers

SLIDE 28

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.28

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTERFACE PHENOMENA – Ferromagnetic / Antiferromagnetic coupling

W. Kuch et al., Nature Materials (2006)

Example of 90° coupling

Co\FeMn(001)\Co

Need both reflectivity (depth information) and imaging (non-averaged)

SLIDE 29

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.29

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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INTERFACE PHENOMENA – Thermal effects

B c

k M Nw J J T . 3 1 . m + = µ

Molecular field N neighbors

Nb Ns

t N N N N ) ( 2

s b b

− − =

1

c

~ ) ( t t T ∆

λ

c

~ ) ( t t T ∆ 1 = λ

G.A.T. Allan, PRB1, 352 (1970)

Thickness-dependent molecular field

U. Gradmann,

Handbook of Magn. Mater. Vol.7, ch.1 (1993)

Naïve model Less naïve Experiments

SLIDE 31

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.31

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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Authors:

J. M. Tonnerre, E. Dooryhee,
J. L. Hodeau (LdC, Grenoble)
C. Dubourdieu, I. Gelard (LMGP, Grenoble)

[La0.7Sr0.3MnO3(46Å)/SrTiO3(31Å)]x15

INTERFACE PHENOMENA – Thermal effects – Ex: LSMO/STO multilayers Probe magnetization profiles in multilayers

Motivations: Model system (epitaxial, similar structure) Tunnelling magnetoresistance (TMR) with high polarization material TMR depends on polarization at the interface: probe buried interfaces Large angle X-ray diffraction

SLIDE 32

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Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

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Models for magnetization profiles

LSMO (12ML) STO STO

Constant profile 1 NM monolayer 2 NM monolayers Symmetric gradient

INTERFACE PHENOMENA – Thermal effects – Ex: LSMO/STO multilayers Experiments Low temp: constant profile High temp: gradient profile

SLIDE 33

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.33

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/ http:// http://lab lab-

neel.grenoble.cnrs.fr

neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ /

INTERFACE PHENOMENA – Fundamental knowledge fed into devices

1 2 3 4

∆R/R (%)

1

1 200 400 600 800

H(Oe)

200

(b) (a) M (10-3 emu)

1 2 3 4

∆R/R (%)

1

1 200 400 600 800

H(Oe)

200

(b) (a) M (10-3 emu)

B.Dieny, V.S.Speriosu, et coll. IBM Almaden (1991)

B. Dieny et al., Phys. Rev. B 43,

1297 (1991).

Basics of spin valves

Free and pinned layers Hysteresis loop Resistance

Free layer Pinned layer (reference) Isolator (TMR) or metal (GMR)

Working area

SLIDE 35

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.35

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/ http:// http://lab lab-

neel.grenoble.cnrs.fr

neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ /

INTERFACE PHENOMENA – Fundamental knowledge fed into devices

Substrate NiFeCr NiFe (3nm) CoFe (2nm) Cu (2nm) CoFe (2nm) CoFe (2nm) Ru (0.9nm) PtMn (10nm) Pinned layer ‘Free’ layer

Need of complementary and accurate local probes (real and reciprocal space) for: layer and/or element selectivity

SLIDE 36

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.36

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/ http:// http://lab lab-

neel.grenoble.cnrs.fr

neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ /

RECENT DEVELOPMENTS – Precessional switching of magnetization Basics of precessional switching

Magnetization dynamics: Landau-Lifshitz-Gilbert equation:

[ ]

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ × + × − = dt d M dt d

s eff

M M H M M α γ 0

: gyromagnetic factor : Effective field (including applied) : Damping coefficient

γ0

Heff

α

1.0
0.5

0.0 0.5 1.0

1.0
0.5

0.0 0.5 1.0

0.1

0.0 0.1 0.2

M

z

Mx My

Magnetization reversal via transverse field > magnetization trajectories

Démonstration: 1999

Typical times: 0.1ns Used in MRAMs Minimized losses Domain wall motion

C. Back et al., Science 285, 864 (1999)

SLIDE 38

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.38

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/ http:// http://lab lab-

neel.grenoble.cnrs.fr

neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ /

RECENT DEVELOPMENTS – Current-induced magnetization reversal Basics

Can be viewed as the GMR-reversed effect Conventionnal hysteresis loop Current-induced magnetization reversal

Group Myers et Ralph, Cornell University (2000)

Simplified architectures (MRAMs etc.) Fully electronic read/write Devices making use of domain wall motion (memory, logic) Unexpected: stationnary GHz oscillators Motivations

SLIDE 39

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.39

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/ http:// http://lab lab-

neel.grenoble.cnrs.fr

neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ /

III-V: achieved. GaMnAs, Tc>=150K when optimized. Clustering of MnAs above 6-8%. Mn convey both spins and doping II-VI: achieved. Ex: CdMnTe. Tc<10K. No clustering. Mn conveys spin, not doping (better for fundamental science). IV: under way. Ex: GeMn. High band gap. Ex: ZnCoO. Issues of clustering. p-doped: paramagnetic or

antiferromagnetic. Prospects: p-doped, field-effect doping

(ZnMgO\ZnCoO\ZnMgO), ZnMnO etc.

RECENT DEVELOPMENTS – Magnetic semiconductors Direct integration of magnetism in electronics « Spin-photo-electronics » Electrical control (field effect control of Tc, anisotropy etc.) Current-induced domain wall motion demonstrated (GaMnAs) Motivations

SLIDE 40

Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.40

Laboratoire Louis Néel, Grenoble, France. Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. .

http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/ http:// http://lab lab-

neel.grenoble.cnrs.fr

neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ /

[1] O. Fruchart, A. Thiaville, Magnetism in reduced dimensions,

C. R. Physique 6, 921 (2005) [Topical issue, Spintronics].

[2] O. Fruchart, Couches minces et nanostructures magnétiques, Techniques de l’Ingénieur, à paraître. [3] O. Fruchart, Epitaxial self-organization: from surfaces to magnetic materials,

C. R. Physique 6 (1), 61-73 (2005) [Topical issue, self-organization at surfaces].

[4] Lecture notes from undergraduate lectures, plus various slides: http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/ [5] G. Chaboussant, Nanostructures magnétiques, Techniques de l’Ingénieur, revue 10-9 (RE51) (2005) [6] Magnetic domains, A. Hubert, R. Schäfer, Springer (1999, reed. 2001) [7] Magnetoelectronics, Ed. M. Johnson, Elsevier Academic Press (2004). [8] The Physics of Ultrahigh-density Magnetic Recording, M. Plumer, J., van Ek, D. Weller, Springer (2001) [9] J.P. Bucher, Magnetism of free and supported metal clusters, in: S.N. Khanna, A.W. Castleman Jr. (Eds.), Quantum Phenomena in Clusters and Nanostructures, in: Springer Series in Cluster Physics, Springer, Berlin, pp. 83–137 (2003). [10] J.P. Bucher, F. Scheurer, Self-organized clusters and nanosize islands on metal surfaces, in: J.S. Miller, M. Drillon (Eds.), Magnetism: Molecules to Materials III, Wiley–VCH, Weinheim, Germany, pp. 211–251 (2002). [11] J.I. Martin et coll., Ordered magnetic nanostructures: fabrication and properties,

J. Magn. Magn. Mater. 256, 449-501 (2003).

[12] R. Skomski, Nanomagnetics, J. Phys.: Cond. Mat. 15, R841–896 (2003). [13] J. Bansmann et al., Magnetic and structural properties of isolated and assembled clusters,

Surf. Sci. Rep. 56, 189 (2005)

(Quelques) tendances et défis du magnétisme en dimensions réduites Fondements et applications à l’électronique de spin

CNRS from mountains

Lab in mountains

Part of the lab (Winter) Part of the lab (Winter) Part of the lab (Summer) Part of the lab (Summer)

TABLE OF CONTENTS

INTRODUCTION TO MAGNETISM – Currents, magnetic fields and magnetization r I B π µ 2 =

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − × = µ r µ.r) ( 3 4

r r B π µ µ

Oersted field Magnetic moment Magnetic material

INTRODUCTION TO MAGNETISM – Hysteresis loops

Hext M

Manipulation of magnetic materials: Application of a magnetic field

H.M

µ − = E

Hext M

M H E d

∫

= µ

INTRODUCTION TO MAGNETISM – Magnetically soft and hard magnetic materials Soft materials

Hard materials

INTRODUCTION TO MAGNETISM – Sources of magnetic energy

) ( . θ ∇ = − = A J E S S ) ( sin 2

θ K E =

H M .

µ − = E

. 2 1 H M µ − = E

Zeeman energy (enthalpy) Magnetocrystalline anisotropy energy Dipolar energy Echange energy

INTRODUCTION TO MAGNETISM – Magnetic characteristic length scales Typical length scale: Bloch wall width λB

( )

θ θ

sin / K dx d A e + =

J/m

J/m

Numerical values

K A/

π λ =

nm 3 2

− = λ nm 100

λ

INTRODUCTION TO MAGNETISM – Magnetization patterns Bulk material

Mesoscopic scale

Nanometric scale

Magnetic recording essentially makes use of single-domain particles

Principle of GMR INTRODUCTION TO MAGNETISM – Giant magnetoresistance D(E) E d d s s

Features

) cos(θ ∝ ∆R

Applications

INTRODUCTION TO MAGNETISM – Tunnelling magnetoresistance Principle of TMR

w E eV E0

ψ ψ ψ E x V dx d m = + − ) ( 2

h

Features

) cos(θ ∝ ∆R

Applications

Media: granular and columnar INTRODUCTION TO MAGNETISM – Magnetic recording : hard disks (media)

Large number of grains per bit

INTRODUCTION TO MAGNETISM – Magnetic recording : hard disks (heads and density)

Read-write heads

Increase of areal density

INTRODUCTION TO MAGNETISM – Magnetic recording : hard disks (superparamagnetism)

~25kT

τ / ) ( t e t P − =

T k E e

τ τ =

s 10

≈ τ

) / ln( τ t T k E

Formalism for thermal excitations

Orders of magnitude Steady increase of anisotropy K for magnetic recording > Some drawbacks > Physical limits? Anisotropy barrier

INTRODUCTION TO MAGNETISM – Magnetic memories : MRAMs Overview

Detail of a cell

TABLE OF CONTENTS

INTERFACE PHENOMENA – Interface anisotropy

Experimental approach: 1/t plot INTERFACE PHENOMENA – Interface anisotropy

Theory

Co/Pt INTERFACE PHENOMENA – Interface anisotropy

Engineering of anisotropy

TABLE OF CONTENTS

COUPLING PHENOMENA – Dipolar energy

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − = ) . ).( . ( 3 . 4