Giant Giant MagnetoresistanceMagnetoresistance

Kómár PéterKómár PéterSolid state physics seminarSolid state physics seminar

25/09/25/09/20082008

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Types of Types of magnetoresistancemagnetoresistance

OOrdinary rdinary MMagnetoagnetoRResistanceesistance

AAnisotropic nisotropic MRMRGGiant iant MRMRTTunneling unneling MRMRCColossal olossal MRMRBBallistic allistic MRMREExtraordinary xtraordinary MRMR

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First achievementsFirst achievements

1856 Thomson (Lord Kelvin)1856 Thomson (Lord Kelvin) (AMR)(AMR)

B B ║║ II → → Increase of resistanceIncrease of resistance

B B ┴ ┴ II → → Decrease of resistanceDecrease of resistance (max (max.. 5%) 5%)

1886 Boltzmann, 1886 Boltzmann, 1911 Corbino1911 Corbino Corbino-Corbino-diskdisk (OMR)(OMR)

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OrdinaryOrdinary MR MR

LorentzLorentz force force → → change of mobilitychange of mobility:: LorentzLorentz force force::

velocity of charged particlesvelocity of charged particles::

Corbino-Corbino-diskdisk:: Effective mobilityEffective mobility::

vFΒvE /ee

EBΒΒEEv 2221

B

ΒE 22eff 1 B

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Corbino-Corbino-diskdisk

IρI’

B 0

I

B = 0

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Anisotropic MRAnisotropic MR

Angle betweenAngle between II andand BB R R = max. = max. at parallel alignmentat parallel alignment B B ┴┴ II →→ OMR OMR

ApplicationApplication: : magnetic sensorsmagnetic sensors electronic compasselectronic compass traffic sensorstraffic sensors non-galvanic non-galvanic

current meter current meter

B

I

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AMR and Hall-effectAMR and Hall-effect

Ohm’s law: Ohm’s law: jj = = σσ EE ,where ,where σσ is a is a matrixmatrix

Diagonal elements: conductivity + AMRDiagonal elements: conductivity + AMR

Off-diag. elements: Hall-effect (Off-diag. elements: Hall-effect (jj ┴┴ BB ┴┴ EEHH))

Bss

ss

ss

B

zxy

xyz

yzx

HH

HH

HH

σ

BB zyxzyx //0

//

jrE HH

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Barber’s pole Barber’s pole magnetic magnetic sensorsensor

Barber’s pole:Barber’s pole:

The sensorThe sensor:: permalloy permalloy basebase (Fe (Fe2020NiNi8080)) Au-Al Au-Al stripsstrips

current flows incurrent flows in 45° → R(B) 45° → R(B) linear near linear near 00

(2 a,b) Dr. Andreas P. Friedrich, Helmuth Lemme, "The Universal Current Sensor” , Sensors weekly (May 1, 2000)

(2a)

(2b)

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Giant MRGiant MR

1988 Fert 1988 Fert & & GrünbergGrünberg (2007 Nobel(2007 Nobel prizeprize)) Multilayered samplesMultilayered samples (Fe-Cr-Fe) (Fe-Cr-Fe) FerromagneticFerromagnetic. – Antiferrom. – Antiferromaagn. gn.

couplingcoupling Decrease in resistance of Decrease in resistance of 10%10% and and

5050%%

Photos: U. Montan (http://nobelprize.org/nobel_prizes/physics/laureates/2007/)

Albert Albert FertFert

Peter Peter GrünbergGrünberg

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Manufacturing Manufacturing multilayered samplesmultilayered samples

19701970ss epitaxial growth epitaxial growth technology technology:: laser evaporationlaser evaporation molecular beammolecular beam sputteringsputtering chemical depositionchemical deposition

FeaturesFeatures:: Si, SiOSi, SiO22, , semiconductorsemiconductor basebase compatible lattice parameters(!)compatible lattice parameters(!) good reproductivitygood reproductivity

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Results of Results of Grünberg Grünberg et et al. al. II..

Fe-Cr-Fe Fe-Cr-Fe samplesample:: GaAs GaAs basebase (epitxial growth (epitxial growth, bcc, bcc)) AF AF coupling between Fe-scoupling between Fe-s [100] easy-[100] easy- (EA)(EA), , [110][110] hardhard axisaxis (HA)(HA)

CheckingChecking:: MOKE (Magneto-MOKE (Magneto-

opticaloptical Kerr effectKerr effect)) light scattering on light scattering on

spin-wavesspin-waves

EA:EA:

G. Binasch, P. Grünberg, F. Saurenbach, W. Zinn (1989) „Enhanced magnetoresistance is layered magnetic structures with antiferromagnetic interlayer exchange” Pys. Rev.

B Vol 39. No. 7

12 12

1

[nm]

EA

HA

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Results of Results of Grünberg Grünberg et et al. al. III.I.

Change of resistanceChange of resistance (T = T(T = TRTRT)) BB║EA: GMR (-1.5%)║EA: GMR (-1.5%) BB║HA: AMR (-0.13%*) és GMR (-1.5%)║HA: AMR (-0.13%*) és GMR (-1.5%) d(Fe) = 8 nm → d(Fe) = 8 nm → ΔΔR/R = 3%R/R = 3% * 25 * 25 nmnm Fe Fe plateplate

G. Binasch, P. Grünberg, F. Saurenbach, W. Zinn (1989) „Enhanced magnetoresistance is layered magnetic structures with antiferromagnetic interlayer exchange” Pys. Rev.

B Vol 39. No. 7

EA:EA: HA:HA:

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Results of Results of Fert Fert et al.et al. I I..

[Fe-Cr][Fe-Cr]nn sample sample:: GaAs GaAs basebase 5 – 60 5 – 60 layerslayers changing changing d(Cr) (6, 3, 1.8, 1.2, 0.9 nm)d(Cr) (6, 3, 1.8, 1.2, 0.9 nm)

→ → change in coupling of Fe layerschange in coupling of Fe layers::FerromagneticFerromagnetic (6 nm) (6 nm)

AntiAntiferromagneticferromagnetic (0.9 (0.9 nm)nm)

(T = 4.2 (T = 4.2 K)K)M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff (1988)

„Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Superlattice” Pys. Rev. Letters Vol. 61, No. 21

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Results of Results of Fert Fert et al.et al. I II.I.

Change of resistanceChange of resistance (T = (T = 4.2 K4.2 K)) ΔΔR/R R/R (-50%) (-50%) andand HHS S (2 T) (2 T) was was

measuredmeasured influence of temperatureinfluence of temperature (T (TRT RT : -25%, : -25%,

1.4 T)1.4 T) EA-HA EA-HA differencedifference, , number of layersnumber of layers, ,

d(Cr)d(Cr)

M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff (1988) „Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Superlattice” Pys. Rev. Letters Vol. 61, No. 21

HA

EA60 (0.9nm)

35 (1.2nm)

30 (1.8nm)

EA

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Theory of Theory of GMRGMR I. I.

RKKY RKKY interactioninteraction ( Ruderman, Kittel (1954), Kasuya (1956), Yosida (1957) )( Ruderman, Kittel (1954), Kasuya (1956), Yosida (1957) )

Coupling between atomic and Coupling between atomic and conducting electronsconducting electrons ( (exchangeexchange intint..,, 22ndnd order perturb. order perturb.))

Based on the Bloch wavefunctionBased on the Bloch wavefunction

applies only for periodic structuresapplies only for periodic structures F-NF-F F-NF-F arrangementarrangement::

couplingcoupling oscillates! oscillates!

Class for physics of the Royal Swedish Academy, “Discovery of the Giant Magnetoresistance” (9 October 2007)

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Theory of Theory of GMRGMR II. II.SpinSpin-dependent-dependent resistance resistance

scattering in FM, and at FM/NM scattering in FM, and at FM/NM interlayerinterlayer

RR-1-1 ~~ σσ ~ N ~ N((EEFF)) Fermi-Fermi-surface changes as an effect ofsurface changes as an effect of

BB

Class for physics of the Royal Swedish Academy, “Discovery of the Giant Magnetoresistance” (9 October 2007)

RR↓↓ == RR↑↑

NN↓↓ ((EEFF)) == NN↑↑ ((EEFF))

RR-- = = RR↓↓ << RR↑↑ = = RR++

B

NN↓↓ ((EEFF)) >> NN↑↑ ((EEFF))

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Theory of Theory of GMRGMR III. III.

SpinSpin-valve-valve d(Nd(NMM) < ) < λλee → → the spin of the spin of ee---s-s is is

constantconstant ↓ ↓ andand ↑ ↑ parallel conduction channelsparallel conduction channels

RR

RRR

2

2

1

Class for physics of the Royal Swedish Academy, “Discovery of the Giant Magnetoresistance” (9 October 2007)

B

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Theory of Theory of GMRGMR IV. IV.

Half metalsHalf metals ↓↓ - - conductingconducting, , ↑↑ - - insulatorinsulator ( (eg. eg.

CrOCrO22)) spin polarization: spin polarization: 100%100%

Class for physics of the Royal Swedish Academy, “Discovery of the Giant Magnetoresistance” (9 October 2007)

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ApplicationApplication – – HDD HDD read read headsheads

ConstructionConstruction layers withlayers with

differingdiffering coercivitycoercivity + AFM + AFM layer layer ((Bruce GurneyBruce Gurney)) RR measuringmeasuring

EfficiencyEfficiency 1991. MR1991. MR 1997. GMR1997. GMR

(Stuart Parkin)(Stuart Parkin)

Magnet Academy, (http://www.magnet.fsu.edu/education/tutorials/magnetacademy/gmr/),IBM Research, (http://www.research.ibm.com/research/gmr.html)

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Tunneling MRTunneling MR

FerromFerromaagn. – gn. – insulatorinsulator– ferrom– ferromaagn.gn. 19751975:: 14%/ - 14%/ - 19821982:: - / - / fewfew%% 19951995:: 30% / 18% 30% / 18% 20072007:: >200% >200%

ApplicationApplication:: spintronicsspintronics magnetic sensorsmagnetic sensors

Class for physics of the Royal Swedish Academy, “Discovery of the Giant Magnetoresistance” (9 October 2007)

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Colossal MRColossal MR

1993 von Helmolt et al.1993 von Helmolt et al. perovskitperovskitee--like like La-Ba-Mn-OLa-Ba-Mn-O annealingannealing, T = 300 K , B = 7 T, T = 300 K , B = 7 T ||ΔΔRR||//R R > 60% (> 60% (steep startsteep start, , no no

saturationsaturation))

R. von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, K. Samwer (1993) „Giant Negative Magnetoresistance in Perovskitelike La2/3Ba1/3MnOx Ferromagnetic Films”, Pys. Rev. Letters Vol. 71,

No. 14

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SpintroniSpintronicscs I. I.

Manipulating both charge and spinManipulating both charge and spin Spin Spin sourcessources: GMR, TMR : GMR, TMR

(C (Current urrent IIn n PPlanelane, C, C PPerpendicular erpendicular P)P) ManipulationManipulation: Spin Torqe Transfer: Spin Torqe Transfer

( (spin of currentspin of current → → magnetization of magnetization of layerlayer))

Reading Reading ((in semiconductorsin semiconductors):): light scatteringlight scattering, , electroluminescenceelectroluminescence, ,

spin valve spin valve, , ballistic spin filteringballistic spin filtering

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SpintroniSpintronicscs II. II.

ApplicationApplication: : MRAM (NVM) MRAM (NVM) transistortransistor laserlaser

Thank you for the Thank you for the attention!attention!