Systèmes Hybrides. Norman Birge Michigan State University

Transcription

1 Systèmes Hybrides Norman Birge Michigan State University

2 Résumé Systèmes F/N Systèmes S/N Systèmes S/F

3 Résumé: Systèmes F/N Accumulation de spin Giant Magnetoresistance (GMR) Spin-transfer torque (STT) L éffet Spin Hall (SHE) D autres sujets: Spin pumping magnetocaloritronics

4 Glossary Ferromagnet Magnetization Torque Spin Majority electrons Aimant ou metal ferromagnétique Aimantation Couple Spin Electrons majoritaires?

5 Switch to blackboard! Spin-polarized transport and spin accumulation Von Son, van Kempen, and Wyder, PRL 58, 2271 (1987) Herschfield & Zhao, PRB 56, 3296 (1997) Valet & Fert, PRB 48, 7099 (1993) Schmidt,, van Wees, PRB 62, R4790 (2000)

6 / o"1*'*, * I G? -V''f, ol^', {* - r V = 0 4 Vl.,'^ 'ov A F V

7 /n?- ra..gi kt.l^4 r' v'a '# 2 ' - -a ' 4,1 = : vw J l / Vn.,, P rq V{ I vi f

8 (9 T, f, ].!Ll_' _ -m ln A /w^' ln z /1A.. n --ul-er -\ n-rt,c""tlr'r*r) ; ( ao?,.io*f c<,

9 ); L t ' r I I t,f"i I t- \ojl\rry\ lwu{}ry,rv- N, l(5 /v,[ t.f f ) trnt r v t,^ v-t- (y 6 /6 /t.( \ %.,, a ( = / { " f^ -- N { -*rtna NtJfn r 0 f I ry

10 @ l J \ ^ V \ l - t - a f,fh --F-fl-- 0'r o'r ory oot 0r0, -tno*f '+J' tjfit -tto' J 'r'- f Y. t? f 5 l &9+ ryrr-\t-j A.&

11 @

12 -l;a ffirfr;t a- a.q +f, -- rl + c? f l -----{-- r, A tst -d1(+-+l

13 ,^* F /nt

14 /W, N '/^.- * >, b =/ 0,( ;- --{ : t r.a + E: Ap q i%?,hnt

15 4 ) A a,-) 0 6*d

16 n \ltc l-& /3 b, t-t' (,n ) \nr \ l ), 1 l='( + I T al ^\- I l- /N./.!

17 Ar i > X'4 -oo : c-)c : C! 6 * (0. / / ( 1t_il lr/r \\ \\ -q7 i tx) +h i F ; 0 \\ \\,rar\x) \\ \ \ \ \ n,- (x=u\ \ /r' ' \ rr (J- \ / o '!r f-_ *l \:-\ X

18 (? -ft-- 4,. l5? l+ 1-1 l_-- e') l / ----L-*1 ^l*

19 g u tn^ (/ylr( o+l a,f - (on). (r) --

20 The first spin injection experiment from F to N: Johnson and Silsbee, PRL 55, 1790 (1985); PRB 37, 5326 (1988) Hanle effect

21 The modern version of the spin injection experiment: Non-local detection of spin accumulation Jedema,, van Wees, Nature 416, 713 (2002).

22 $;^ tuclr^r^\r/jt,* iw r f nr lr A s tn't^sj

23 An unexpected discovery: Giant Magnetoresistance in metallic multilayers Binasch, Grunberg, Baibich, Fert, PRL 61, 2472 (1988). PRB 39, 4828 (1989)

24 Cartoon explanation of Giant Magnetoresistance: The 2-current series resistor model Bass & Pratt, JMMM 200, 274 (1999)

25 R Giant Magnetoresistance in Exchange Biased Spin Valve (EBSV) Good control of antiparallel (AP) and parallel (P) states AF F2: free layer N is thick enough to uncouple two F layers F1 is pinned by exchange bias coupling to antiferromagnet (AF) Derive R P and R AP on whiteboard! AP R = (R AP R P ) > 0 P 0 H

26 ! AA^^LAI /-Uvrl,ol lvuh -- vyr - D A lcrfi K.t 'vul' AA- 1&r A - t+k,l [A^ * A^? [(

27 CPP spin-polarized transport in ferromagnetic/non-magnetic metal (F/N) Multilayers i CPP F N F N F CPP models Two-current series-resistor model (2CSR): long spin-flip diffusion lengths Finite F sf & N sf : Valet & Fert model t F t N F sf t F N sf t N CPP experiments determined fundamental spin-polarized transport parameters for F-metals & -alloys, N-metals & -alloys and their interfaces An important CPP parameter: Asymmetry of spin-orientation-dependent electron scattering In F layers: F = (M, s) F (0 1) F F = (M, s) 4 F F F * F F At F/N interfaces: AR F/ N AR F/ N = (M, s) = (M, s) AR AR F / N F / N AR AR F / N F / N AR * F/ N AR F/ N AR 4 F/ N

28 Spin-memory loss in F-metals and -alloys CPP exchange-biased spin valve (EBSV) At 4.2 K AR = AR AP - AR P 2CSR model free pinned Nb Py Cu Py FeMn Nb CPP Current AR (fm 2 ) Py sf infinity t Py (nm) Py sf 5.5 nm Extension of CPP Valet-Fert theory to Spin Valve case Py = Permalloy = Ni 84 Fe 16 Py sf 5.5 1nm

29 A new and interesting theoretical prediction in 1996: Spin-transfer torque (STT) Landau-Lifshitz-Gilbert equation: Spin-torque term Requires large current densities: J 10 7 A/cm 2

30 Cartoon explanation of spin-transfer torque (STT): Waintal, Myers, Brouwer & Ralph, PRB 62, (2000) Spin-polarized current incident on F with non-collinear M.

31 Magnetic switching by spin-transfer torque: Katine, Buhrman, Ralph, PRL 84, 3149 (2000) Landau-Lifshitz-Gilbert equation with spin-torque:

32 Spin torque and MRAM Go to Everspin web page:

33 Spin Hall effect: D yakonov & Perel, Phys. Lett. A 35, 459 (1971) Hirsch, PRL 83, 1834 (1999) Zhang, PRL 85, 393 (2001) Spin-orbit interaction: Zhang, PRL 85, 393 (2001) Figure from Takahashi & Maekawa, Sci. Technol. Adv. Mater. 9, (2008)

34 First measurement of Spin Hall effect in metals: Valenzuala & Tinkham, Nature 442, 176 (2006).

35 Valenzuala & Tinkham, continued

36 Magnetic switching by Spin Hall effect: Liu, Ralph, Buhrman, PRL 109, (2012) Large enhancement due to geometrical factor: Area of spin transfer: A = Lw Area of current flow: a = Dw Each electron passing through Pt layer transfers many times hbar of angular momentum to Co layer

37 Topics not covered: Spin pumping: Tserkovnyak, Brataas & Bauer, PRL 88, (2002). Works in ferromagnetic insulators!

38 Topics not covered: Spin caloritronics: See special issue of Solid St. Commun. 150, 459 (2010) Preface by Bauer, MacDonald & Maekawa