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Spin depend electron transport: AMR, GMR

Spin depend electron transport: AMR, GMR. Lecture 2. Magnetorezystancja. Anizotropowa Magnetorezystancja AMR origin spin – orbit coupling (  1960) Gigantyczna Magnetorezystancja GMR 1986 – oscillatory interlayer exchange coupling in Fe/Cr/Fe multilayers

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Spin depend electron transport: AMR, GMR

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  1. Spin depend electron transport: AMR, GMR Lecture 2

  2. Magnetorezystancja Anizotropowa Magnetorezystancja AMR origin spin – orbit coupling (1960) Gigantyczna Magnetorezystancja GMR 1986 – oscillatory interlayer exchange coupling in Fe/Cr/Fe multilayers P. Grünberg et al. Phys Rev.Lett. 57 (1986), 2442 1988 – GMR in Fe/Cr/Fe multilayers M. N. Baibich,..., A.Fert,.. et.al. Phys Rev.Lett. 61 (1988), 2472

  3. Ohms law for galvanomagnetic effects m = M / |M| mx= sinq cosf my= sinq sinf mz= cosf, • magnetoresistivityDr = r- r

  4. Galvanomagnetic effects in the plane of thin film • Longitudinal magnetoresistivity effect • Transversal magnetoresistivity effect

  5. Angle dependence of the longitudinal magnetoresistivity U = R i U = Ri

  6. Magnetic field dependence of the longitudinal magnetoresistivity effect (AMR) if i || Hq =f

  7. I = const Ua magnetoresistance - - U U R R D R a p a p = = »  % 5 100 U R R p p p Giant Magnetoresistivity - GMR I = const  10 nm Up ferromagnet nonferromagnet (Cu) ferromagnet

  8. Thickness dependence of spacer layer

  9. GMR is isotropic in respect to the current

  10. Below, structure of Fe film/ Cr wedge/ Fe whisker illustrating the Cr thickness dependence of Fe-Fe exchange. Above, SEMPA image of domain pattern generated from top Fe film. (J. Unguris et al., PRL 67(1991)140.)

  11. M M I R small Spin depend conductivity I R large

  12. Density of states in 3-d metals GMR  due scattering into the empty quantum states above the Fermi level D(EF) For ferromagnetic 3d metals D(EF)  D(EF)    

  13. Energy Energy Energia EF d d d s s s Spin Spin polarization of ferrmagnets Magnetization Density of states

  14. Pseudo spin valve (PSV) M(H) & R(H) Two stages charactristics

  15. Magnetic dots Co (4nm) Cu (3nm) NiFe (6nm)

  16. 0 1 Magnetic Random Access Memory (MRAM) ścieżka przewodząca antyferromagnetyk ferromagnetyki nieferromagnetyczna międzywarstwa  150 nm

  17. Zastosowania pseudo-zaworów spinowych • Nieulotne pamięci magnetyczne o dostępie swobodnym (Magnetic Random Access Memory) • matryca złożona z komórek pamięciowych: elementów PSV • bit informacji reprezentowany poprzez wzajemną orientację wektorów namagnesowania warstw ferromagnetycznych twardej i miękkiej; • zapis poprzez przemagnesowanie silniejszym prądem; • odczyt poprzez detekcję zmiany rezystancji • informacja przechowywana jest po zaniku zasilania; • szybki zapis i odczyt, mały pobór mocy; • cykle zapisujące są nieniszczące; • odporność na promieniowanie jonizujące.

  18. M(H) magnetization Spin-Valve (SV) R(H) magnetoresistance

  19. Spin valve (SV) – M(H) & R(H) high magnetoresistance field sensitivity

  20. Different GMR Structures

  21. Conclusions • GMR can only be observedif at latest two ferromagnetic layers are separated by non-magnetic metal layers • GMR has a maximum, if the magnetization vectors in adjacent • F-layers is antiparallel • CPP has a larger effect than CIP • GMR is a direct image of the magnetic hysteresis • GMR is much larger than AMR • GMR increases with decreasing temperature • GMR depends on the number of F/M interfaces • For the GMR effect it is not important how the antiparallel orientation of the magnetization vectors in adjacent ferromagnetic layers is achivied (exchange bias F/AF or exchange coupling SAF)

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