Giant MagnetoresistanceKmr Pter Solid state physics seminar 25/09/2008

Types of magnetoresistanceOrdinary MagnetoResistanceAnisotropic MRGiant MRTunneling MRColossal MRBallistic MRExtraordinary MR

First achievements1856 Thomson (Lord Kelvin) (AMR)B I Increase of resistanceB I Decrease of resistance (max. 5%) 1886 Boltzmann, 1911 CorbinoCorbino-disk (OMR)

Ordinary MRLorentz force change of mobility:Lorentz force: velocity of charged particles:

Corbino-disk:Effective mobility:

Corbino-disk

Anisotropic MRAngle between I and BR = max. at parallel alignmentB I OMRApplication: magnetic sensorselectronic compasstraffic sensorsnon-galvanic current meter

AMR and Hall-effectOhms law: j = E ,where is a matrix

Diagonal elements: conductivity + AMR

Off-diag. elements: Hall-effect (j B EH)

Barbers pole magnetic sensorBarbers pole:

The sensor:permalloy base (Fe20Ni80)Au-Al strips current flows in 45 R(B) linear near 0(2 a,b) Dr. Andreas P. Friedrich,Helmuth Lemme, "The Universal Current Sensor , Sensors weekly (May 1, 2000) (2a)(2b)

Giant MR1988 Fert & Grnberg (2007 Nobel prize)Multilayered samples (Fe-Cr-Fe) Ferromagnetic. Antiferromagn. couplingDecrease in resistance of 10% and 50%Photos: U. Montan (http://nobelprize.org/nobel_prizes/physics/laureates/2007/)Albert FertPeter Grnberg

Manufacturing multilayered samples1970s epitaxial growth technology:laser evaporationmolecular beamsputteringchemical depositionFeatures:Si, SiO2, semiconductor basecompatible lattice parameters(!)good reproductivity

Results of Grnberg et al. I.Fe-Cr-Fe sample:GaAs base (epitxial growth, bcc)AF coupling between Fe-s[100] easy- (EA), [110] hard axis (HA) Checking:MOKE (Magneto- optical Kerr effect)light scattering on spin-wavesG. Binasch, P. Grnberg, F. Saurenbach, W. Zinn (1989) Enhanced magnetoresistance is layered magnetic structures with antiferromagnetic interlayer exchange Pys. Rev. B Vol 39. No. 7

Results of Grnberg et al. II.Change of resistance (T = TRT)BEA: GMR (-1.5%)BHA: AMR (-0.13%*) s GMR (-1.5%)d(Fe) = 8 nm R/R = 3%* 25 nm Fe plateG. Binasch, P. Grnberg, F. Saurenbach, W. Zinn (1989) Enhanced magnetoresistance is layered magnetic structures with antiferromagnetic interlayer exchange Pys. Rev. B Vol 39. No. 7

Results of Fert et al. I.[Fe-Cr]n sample:GaAs base5 60 layerschanging d(Cr) (6, 3, 1.8, 1.2, 0.9 nm) change in coupling of Fe layers:Ferromagnetic (6 nm)Antiferromagnetic (0.9 nm)(T = 4.2 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

Results of Fert et al. II.Change of resistance (T = 4.2 K)R/R (-50%) and HS (2 T) was measuredinfluence of temperature (TRT : -25%, 1.4 T)EA-HA difference, number of layers, 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

Theory of GMR I.RKKY interaction ( Ruderman, Kittel (1954), Kasuya (1956), Yosida (1957) )Coupling between atomic and conducting electrons (exchange int., 2nd order perturb.)Based on the Bloch wavefunction applies only for periodic structuresF-NF-F arrangement: coupling oscillates!Class for physics of the Royal Swedish Academy, Discovery of the Giant Magnetoresistance (9 October 2007)

Theory of GMR II.Spin-dependent resistance scattering in FM, and at FM/NM interlayerR-1 ~ ~ N(EF)Fermi-surface changes as an effect of BClass for physics of the Royal Swedish Academy, Discovery of the Giant Magnetoresistance (9 October 2007)

Theory of GMR III.Spin-valved(NM) < e the spin of e--s is constant and parallel conduction channelsClass for physics of the Royal Swedish Academy, Discovery of the Giant Magnetoresistance (9 October 2007)

Theory of GMR IV.Half metals - conducting, - insulator (eg. CrO2)spin polarization: 100%Class for physics of the Royal Swedish Academy, Discovery of the Giant Magnetoresistance (9 October 2007)

Application HDD read headsConstructionlayers with differing coercivity+ AFM layer (Bruce Gurney) R measuringEfficiency1991. MR1997. GMR (Stuart Parkin)Magnet Academy, (http://www.magnet.fsu.edu/education/tutorials/magnetacademy/gmr/), IBM Research, (http://www.research.ibm.com/research/gmr.html)

Tunneling MRFerromagn. insulator ferromagn.1975: 14%/ -1982: - / few%1995: 30% / 18%2007: >200%Application:spintronicsmagnetic sensorsClass for physics of the Royal Swedish Academy, Discovery of the Giant Magnetoresistance (9 October 2007)

Colossal MR1993 von Helmolt et al.perovskite-like La-Ba-Mn-Oannealing, T = 300 K , B = 7 T|R|/R > 60% (steep start, no saturation)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

Spintronics I.Manipulating both charge and spinSpin sources: GMR, TMR (Current In Plane, C Perpendicular P)Manipulation: Spin Torqe Transfer (spin of current magnetization of layer) Reading (in semiconductors): light scattering, electroluminescence, spin valve, ballistic spin filtering

Spintronics II.Application: MRAM (NVM) transistorlaser

Thank you for the attention!