1. Bulk and Interface Properties of Multilayer Systems Edson Passamani Caetano Universidade Federal do Espírito Santo Physics Departament/Espírito Santo/Vitória/Brazil 530 km Winter season

2. Studied problems Non-collinear magnetic coupling Exchange bias effect Sample preparations Fe/Mn/Fe trilayers (MBE) FeNi/FeMn/FeNi trilayers (Sputtering) Mössbauer results Fe/Mn/Fe trilayers FeNi/FeMn/FeNi trilayers General Remarks Introduction Thin films/Multilayers Relevant discorverings in multilayers Outline

3. Thin films/Multilayers If the effusion cells can be independently controlled substrate materials A+B substrate material A substrate System with one of its dimension in nanometer scale

4. From especial issue of J3M (1999) ~1400 AFM Coupling GMR RKKY Relevant Discoverings in Multilayers Exchange bias + Spin-Valves

5. Studied Systems Influence of interfacial roughness/alloy on the: (i) Non-collinear coupling of Fe/Mn/Fe trilayers (ii) EB effect in FeNi/FeMn/FeNi trilayers

6. AFM FM 90 o FM 90 o AFM 90 o FM M 1 upper Fe M 2 lower Fe Wegded-sample: Fe(10nm)/Cr(xnm)/Fe(10nm) Pictures from Grunberg´s group How do Fe layers interact in the simplest multilayer system? Fe AFM

7. Yan et al. have found non-collinear coupling in Fe/Mn/Fe (PRB 59 (1999)) Fe (5nm) Mn Fe(5nm) 0.5 nm0.9 nm 1.4 nm

8. Sample preparation : MBE (KULeuven) Vacuum during the deposition 6x10 -11 mbar Substrate temperature (Ts) = 50-175 ºC MgO(001) 4 up to 9 nm – nat Fe Rate of 0.16 Å/s (lower layer) 57 Fe (1nm) deposited in both interfaces with 0.07 Å/s MgO (001) Mn (x nm) deposited with 0.04 Å/s nat Fe 4 nm Si – 8 nm MgO(001) Ag(100nm) or

9. Reflection High Energy Electron Diffraction (RHEED) – [KULeuven] Rutherford Back-Scaterring (RBS) – [KULeuven] X-ray Diffraction (low and high angles) – [KULeuven] Structural characterization VSM and PPMS – [KULeuven and UFES/Brazil] X-ray Magnetic Circular Dicroism (XMCD) – [LNLS/Brazil] Ferromagnetic Ressonance (FMR) – [UFG/Brazil] Magnetic Characterization Hyperfine Characterization Conversion Electron Mössbauer Spectroscopy (CEMS) – [ KU Leuven and UFES/Brazil] Experimental Characterization Methods

10. 57 Fe Mössbauer Spectroscopy +1/2 +3/2 -3/2 -1/2 +1/2 -1/2 57 Fe nucleus γ-rays direction Mn 57 Fe MgO(001) Ideal interface Interface B hf B hf bulk ( nat Fe layer) Relative transmission (a.u.) V(mm/s) Transmission mode M L K 10% 14.4 keV e-e- 80% 7.3 keV 90% 100% 14.4 keV Relative emission Emission mode V (mm/s)

11. MgO/Fe(5nm)/Mn(0.5nm)/Fe(5nm) prepared at different Ts 0.4 nm Fe bulk 0.6 nm Fe bulk 57 Fe Mn Si MgO(001) Si MgO(001)

12. Field direction MgO/Ag/(100nm)/Fe(10nm)/Mn(x nm)/Fe(5nm) x = 1.4 nm -0.1 0.1 0 T S =50 0 C - 0.3 0 0.3 M/M S x=1.0 nm  0 H(T) Magnetometry: Field Applied // to the Film Plane 0.3 0 -0.3 M/M s μ o H(T) x = 1.0 nm E T = E anistopry + E Zeeman + E exchange Coupling energy exch

13. MgO/Ag(100nm) substrate (T S = 50 o C) Upper Fe layer Lower Fe layer θ=47 0 θ~90 0

14. MgO/Fe(5nm)/Mn(1nm)/Fe(5nm) T S =150 o C MgO/Ag(100nm)/Fe(10nm)/Mn(1nm)/Fe(5nm) T S =50 o C 17 % of bulk α-Fe 38% of bulk α-Fe  =47 o  =72 o

15. EB effect 2 nd problem to be shown Meiklejohn and Bean JAP 33 (1962) 1328 EB effect - Shifting of the M(H) curve along field axis H c1 H c2 H eb = [H C1 –H C2 ]/2

16. Py (30 nm) Py (10nm) FeMn (15 nm) WTi (10nm) Si (100) Deposition conditions: Vacuum: 5 x 10 -8 Torr Argon working pressure (P W ): 2, 5 and 10 mTorr; Applied field during deposition ( 460 Oe) T S : 20 o C Sample preparation: Sputtering (CBPF) Py=Ni 80 Fe 20 AFM FM Samples: A2, A5 and A10 P W = 2, 5 and 10 mTorr

17. Interfacial effect/EB system H eb values reduce with roughness [Nogués et al., PRB 59 (1999) 6984] H eb values increase with roughness [Uyama et al., J. Magn. Soc. Jpn. 21 (1997) 911]

18. Samples: A2, A5 and A10 P W = 2, 5 and 10 mTorr X-ray Reflectivity data

19. X-ray Reflectivity results SampleThickness and roughness (nm) from the fits A2Py(30.5)/0.3/FeMn(13.6)/0.7/Py(10.1) A5Py(30.6)/0.8/FeMn(13.8)/1.1/Py(10.3) A10Py(30.2)/1.0/FeMn(13.1)/2.7/Py(10.1) Py FeMn Upper Interface Lower interface Si/WTi/Py(30)/FeMn(15)/Py(10)/WTi P W = 2, 5 and 10 mTorr (A2, A5 and A10)

20. Samples: A2 and A10 P W = 2 and 10 mTorr

21. SampleH eb1 (Oe)H C1 (Oe)H eb2 (Oe)H C2 (Oe) A241.43.1116.18.4 A525.73.7101.611.2 A1029.05.562.420 Magnetometry Si/WTi/Py(30)/FeMn(15)/Py(10)/WTi P W = 2, 5 and 10 mTorr (A2, A5 and A10) H eb values decrease while H c values increase with roughness

22. Si/WTi(10)/Py(30)/FeMn(15)/Py(10)/WTi(10) P W = 2, 5 and 10 mTorr (A2, A5 and A10)

23. Components Hyperfine parameters Samples A2A5A10 Ni 80 Fe 20 (Py) B hf (T) 29  229  128  2  (mm/s)0.04  0.050.05  0.01-0.02  0.09 A %443935 FeMn + AFM and/or PM interface phases A %565758 FM interfacial alloy B hf (T)- 16.6  0.116.2  0.4  (mm/s) - -0.08  0.01-0.06  0.01 A %-47 Hyperfine parameters “chemical roughness (alloy) ” exceeds the interfacial roughness Ni 80 Fe 20 52% Fe 50 Mn 50 48% Calculated fraction

24. Proposal model Transversal view Ni Fe Roughness and/or alloy FM phase at the interface AFM (FeMn + (NiFe) x Mn y ) Mn Fase PM At the interface Rich- Fe – phase from the NiFe (sextet) NiFe FeMn Py (30 nm) Py (10nm) FeMn (15 nm) WTi (10nm) Si (100)

25. In trilayer systems, the upper interface is usually rougher than the lower one. In addition, the “chemical roughness (alloy)” is in general larger than the interfacial/surface roughness. The magnetic coupling angles in Fe/Mn/Fe trilayers are related to their interfacial roughnesses and therefore it is not due to the quasi-helicoidal AFM state of Mn layer in the trilayer. Bulk magnetic properties of multilayer systems are intrinsically associated with their interface properties. General Remarks The Py/FeMn/Py trilayers H eb  1/roughness and H C  roughness. Theirs values are intrinsically related to the fraction of each Mössbauer component.

26. Prof. Dr. André Vantomme (KULeuven-Belgium) Prof. Dr. Elisa Baggio-Saitovitch (CBPF/Brazil) Prof. Dr. Fernando Pelegrini (IFG/Brazil) Dr. Bart de Groot (KULeuven-Belgium) Dr. Bart Croonenborghs (KULeuven-Belgium) Dr. Valberto Pedruzi Nascimento (CBPF/Brazil) MSc. Breno Segatto (UFES/Brazil) MSc. Francisco Almeida (KULeuven-Belgium) UFES KULeuven IF - UFG CBPF Sponsors: Thank you!

27. NiFe phase FM H direction during deposition Spins FM planar Spins AFM planares FeMn Spins non-colinear x Frustation phase PM and AFM (FeMn and NiFeMn) Ni(+)FeMn PM clusters Spins AFM planar NiFeMn x x x Spins FM perpendicular Magnetic structure model