Spin injection and absorption in antiferromagnets

Transcription

1 Spin injection and absorption in antiferromagnets L. Frangou (PhD), P. Merodio (PhD 2014), G. Forestier (Post-Doc), A. Ghosh, S. Oyarzún, S. Auffret, U. Ebels, M. Chshiev, H. Béa, L. Vila, O. Boulle, G. Gaudin, M. Miron, W. E. Bailey, S. Gambarelli, and V. Baltz A. Manchon (KAUST), A. Mougin (LPS), D. Spenato (LMB) JCJC 2015 ASTRONICS CRG 2016 KAUST-SPINTEC-UTEXAS 1

2 Antiferromagnetic metals 0.38 nm Materials properties for transport: - Conduction: metal/insulator/semiconductor - Spin-orbit: crystal and spin structure heavy vs light elements - Threshold for device function: T Néel (at the nanoscale) Review manuscript, Arxiv:

3 Insulators Semiconductors / Semimetals Review manuscript, Arxiv:

4 Spin injection and absorption in an antiferromagnet current spin AF Fundamental parameters to be determined: -! "/$ ' the interfacial spin mixing conductance - λ the spin penetration length and relaxation mechanisms - T N the critical temperature at the nanoscale g )/* S λ The spin pumping method may give access to all these parameters 4

5 Spin current generation and absorption Spin pumping - creation of a spin current (I S ) induced by the non-equilibriumdynamics of a magnetic order (e.g. ferromagnetic resonance) Spin Injector Conductor Sink ( g eff S ) I S = 2e ħ g eff S γ7 ħ ( µ 0 h rf ) 7 P 8 π α 7 Y. Tserkovnyak et al, PRL (2002), RMP (2005) nm ferromagnet spacer antiferromagnet 5

6 Detecting spin current absorption Reflection: damping Transmission: inverse spin Halleffect ( g eff S ) (g eff ) 6

7 Detecting spin current absorption Reflection: damping absorption spectrum of NiFe ΔH pp H 9.6 GHz ( g eff S ) 2 ΔH pp = 2ωα/( 3 γ ) + ΔH 0 avec α = α 0 + α p α p = γ ħ g eff / (4 π M S A )X*Y t NiFe ) 7

8 Experimental setup Waveguide at 300K with variable frequency (2-24 GHz) Cavity at 9.6 GHz with variable temperature (2-300K) 500 µm 7 mm 8

9 Spin penetration length Room temperature spin penetration length nm - λ IrMn = 0.7 nm ~ ferro. λ FeMn = 1.6 nm ~ para. - Relaxation mechanisms still under debate - Any influence from the magnetic order on spin pumping? Ccl of our APL 104 (2014): Future works could involve ( ) variable temperature for studies of the para- to antiferro-magnetic transition temperature: difficult to determine by many other techniques. P. Merodio et al & V. Baltz, APL 104 (2014) 9

10 Interface transparency current spin AF g^/_* S λ Interfacial engineering - Quality of the interface - Electrical nature of the materials - e. g. Hf interlayer between FeCoB and PtMn Y. Ou et al, PRB (2016) Arxiv:

11 Influence of the antiferromagnetic order Review manuscript, Arxiv: J. Bass and W. P. Pratt, JPCM (2007) 11

12 Influence of the antiferromagnetic order Variable temperature nm - dα p extra enhancement L. Frangou et al & V. Baltz, PRL (2016) 12

13 Theoretical model Spin pumping and fluctuations of the spin sink magnetic order - enhancement of the spin conductance across the interface Sink Spin Injector Y. Ohnuma et al, PRB (2014) Transposed to our case p a 1 = gcu / IrMn 4pS 0N SI Spin Injector Sink g Cu / IrMn 8pJ S N 2 2 sd 0 int = 2 å! N SS k 1 W rf Im c R k ( W ) rf χ enhanced near T crit 13

14 Magnetic susceptibility A way to access to the susceptibility of thin materials IrMn T crit L. Frangou et al, PRL (2016) W. Lin et al, PRL (2016) Z. Qiu et al, Nat. Comm. (2016) χ IrMn δg ef/@def δα g - to date, most technique are volume sensitive - we have access to a unique surface sensitive tool 14

15 Critical temperature for the IrMn magnetic phase transition Criticaltemperatures and finitesizescaling T IrMn (K) crit 100 C v t IrMn (nm) - For t IrMn < n 0 : T IrMn crit IrMn ( t ) = T ( bulk ) IrMn N t IrMn 2n 0 - d n 0 d spin-spin correlation length interatomic distance R. Zhang and R. F. Willis, PRL (2001) - Fit => n 0 = 2.7 ± 0.1 nm ~ ferro. C V data point from D. Petti et al, APL (2013) 15

16 Influence of then environment on T crit (K) Various caps - in particular Pt and Pd may polarize, extend the effective thickness and thus enhance T crit T IrMn crit /IrMn0.8/Cap2 (nm) T crit is robust against the environment 0 MgO Al Ru Cap Pd Pt 16

17 Influence of static vs. dynamic magnetic order T IrMn (K) crit L. Frangou et al & V. Baltz, PRL (2016) Bulk T N Paramagnetic Antiferromagnetic Magnetic phase transition of IrMn at 300K - paramagnetic below t IrMn = 2.7 nm - antiferromagnetic above t IrMn (nm) 300 K Limited influence of the magnetic order in this IrMn: polycrystalline and non-collinear - a p is constant above t IrMn = 2 nm (< 2.7 nm) meaning that a p para. = a p antiferro. Practical use of antiferromagnetic spintronics - fundamental effects (enhanced spin pumping) - parameters for applications (T N,FiniteSize ) P. Merodio et al & V. Baltz, APL (2014) 17

18 Detecting spin current absorption Reflection: damping Transmission: inverse spin Halleffect (ISHE) ( g eff S ) (g eff ) -! "/$ ' interfacial spin mixing conductance - λ spin penetration length - θ IrMn ISHE (= I S /I C ) amplitude of the spin-orbit coupling 18

19 Inverse spin Hall effect Inverse spin Hall effect in I C = RI S tanh ) t IrMn = K I S = 2e ħ g Cu/IrMn S γ 7 ħ ( µ 0 h rf ) 7 P 8 π α 7 L. Frangou et al & V. Baltz, unp. - intraband vs. interband K. Gilmore et al., PRL (2007) - enhanced damping (g Cu/IrMn ) at the IrMn magnetic phase transition hidden by the NiFe damping (1/a 2 ) 19

20 Summary JCJC 2015 ASTRONICS CRG 2016 KAUST-SPINTEC-UTEXAS Use examples of studies of spin injection and absorption in antiferromagnetic materials by the spin pumping method - interfacial engineering via the interfacial spin-mixing conductance - spin penetration length - Néel temperature and magnetic susceptibility (at the nanoscale) - s-o interactions with the ISHE detection L. Frangou et al, PRL (2016) P. Merodio et al, APL 104 (2014), PRB (2014), APL 105 (2014) More to read in the following reviews - H. V. Gomonay, V. M. Loktev, Low Temp. Phys. 40, 22 (2014) - T. Jungwirth, X. Marti, P. Wadley, J. Wunderlich, Nat. Nano. 11, 231 (2016) - V. Baltz, A. Manchon, M. Tsoi, T. Moriyama, T. Ono, Y. Tserkovnyak, Arxiv: Open post-doctoral position at SPINTEC for two years from November 2016 CRG KAUST-SPINTEC-UTEXAS 20 vincent.baltz@cea.fr