giant magnetoresistance kómár péter solid state physics seminar 25/09/2008
TRANSCRIPT
Giant Giant MagnetoresistanceMagnetoresistance
Kómár PéterKómár PéterSolid state physics seminarSolid state physics seminar
25/09/25/09/20082008
2
Types of Types of magnetoresistancemagnetoresistance
OOrdinary rdinary MMagnetoagnetoRResistanceesistance
AAnisotropic nisotropic MRMRGGiant iant MRMRTTunneling unneling MRMRCColossal olossal MRMRBBallistic allistic MRMREExtraordinary xtraordinary MRMR
3
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)
4
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
6
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
7
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
8
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)
9
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
10
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
11
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
12
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:
13
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
14
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
15
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)
16
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))
17
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
18
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)
19
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)
20
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)
21
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
22
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
23
SpintroniSpintronicscs II. II.
ApplicationApplication: : MRAM (NVM) MRAM (NVM) transistortransistor laserlaser