Exchange springs and exchange bias           studied with nuclear methods                    Francisco Miguel Cruz Sim˜es ...
OutlineMagnetism and magnetic interactions  Ferromagnetism and antiferromagnetism  Interlayer coupling  Exchange biasResea...
Magnetism and magnetic interactions     Magnetism and magnetic interactionsFrancisco Almeida (IKS)              Doctoral d...
Magnetism and magnetic interactions         Ferromagnetism and antiferromagnetismFerromagnetsFerromagnetic hysteresis     ...
Magnetism and magnetic interactions   Ferromagnetism and antiferromagnetismAntiferromagnetsAntiferromagnets have no net ma...
Magnetism and magnetic interactions   Ferromagnetism and antiferromagnetismMagnetic interactions    Between ferromagnetic ...
Magnetism and magnetic interactions   Interlayer couplingInterlayer couplingCoupling between ferromagnetic layers separate...
Magnetism and magnetic interactions                     Exchange biasExchange biasExample of an oxidized cobalt thin film ...
Magnetism and magnetic interactions                      Exchange biasExchange biasExample of an oxidized cobalt thin film...
Magnetism and magnetic interactions                         Exchange biasExchange biasExample of an oxidized cobalt thin f...
Researched systems   Surface spin-flop in Fe/CrSurface spin-flop in an Fe/Cr superlatticeFrancisco Almeida (IKS)          ...
Researched systems        Surface spin-flop in Fe/CrFe/Cr superlatticeMultilayer consisting of 22 repetitions of an Fe/Cr ...
Researched systems   Surface spin-flop in Fe/CrFe/Cr superlatticeMultilayer consisting of 22 repetitions of an Fe/Cr bilay...
Researched systems               Surface spin-flop in Fe/CrFe/Cr superlatticeMagnetic response                            ...
Researched systems               Surface spin-flop in Fe/CrFe/Cr superlatticeMagnetic response                            ...
Researched systems    Surface spin-flop in Fe/CrSurface spin-flop               (S)Transition (HC ) that causes a top spin...
Researched systems    Surface spin-flop in Fe/CrSurface spin-flop               (S)Transition (HC ) that causes a top spin...
Researched systems   Surface spin-flop in Fe/CrPolarized Neutron ReflectometrySimilar to X-ray reflectometry.     Sensitive...
Researched systems                   Surface spin-flop in Fe/CrPolarized Neutron ReflectometryResults                    μ...
Researched systems       Surface spin-flop in Fe/CrPolarized Neutron ReflectometrySpins configuration: surface spin-flop t...
Researched systems   Exchange bias in Fe-Pt alloys Exchange bias in Fe-Pt heterostructuresFrancisco Almeida (IKS)         ...
Researched systems   Exchange bias in Fe-Pt alloysFe-Pt heterostructures    Origin of exchange bias notoriously difficult to...
Researched systems   Exchange bias in Fe-Pt alloysFe-Pt heterostructures    Origin of exchange bias notoriously difficult to...
Researched systems   Exchange bias in Fe-Pt alloysFe-Pt heterostructures    Origin of exchange bias notoriously difficult to...
Researched systems       Exchange bias in Fe-Pt alloys ¨Mossbauer spectrometry                  Source                    ...
Researched systems   Exchange bias in Fe-Pt alloysFe-Pt alloys    FePt3 ( Antiferromagnetic, L12 )    FePt ( Ferromagnetic...
Researched systems   Exchange bias in Fe-Pt alloysFe-Pt alloys    FePt3 ( Antiferromagnetic, L12 )                        ...
Researched systems   Exchange bias in Fe-Pt alloysMagnetism of FePt3a) T < 160 K: Q1 wave mode, uncompensated (110) surfac...
Researched systems         Exchange bias in Fe-Pt alloysFePt/FePt3 (110) bilayersMagnetic response                        ...
Researched systems                                    Exchange bias in Fe-Pt alloysFePt/FePt3 (110) bilayersExchange bias ...
Researched systems                                    Exchange bias in Fe-Pt alloysFePt/FePt3 (110) bilayersExchange bias ...
Researched systems   Exchange bias in Fe-Pt alloysOff-stoichiometric Fe-Pt filmWhat happens if we field cool a mixture of F...
Researched systems                   Exchange bias in Fe-Pt alloysOff-stoichiometric Fe-Pt filmWhat happens if we field coo...
Researched systems   Exchange bias through ion implantation Exchange bias through ion beam synthesisFrancisco Almeida (IKS...
Researched systems   Ion implantationIon implantation                                                Ion source           ...
Researched systems   Ion implantationIon beam synthesis    New method for obtaining exchange bias. Francisco Almeida (IKS)...
Researched systems   Ion implantationIon beam synthesis    New method for obtaining exchange bias.          Reactive impla...
Researched systems   Ion implantationIon beam synthesis    New method for obtaining exchange bias.          Reactive impla...
Researched systems    Ion implantationExchange bias in oxygen implanted cobaltExampleThin cobalt film implanted with       ...
Researched systems    Ion implantationExchange bias in oxygen implanted cobaltExampleThin cobalt film implanted with       ...
Researched systems   Ion implantationExchange bias in oxygen implanted cobaltLoop shape analysis                          ...
Researched systems     Ion implantationExchange bias in oxygen implanted cobaltEffect of implantation energy on the exchan...
Researched systems                              Ion implantationExchange bias in oxygen implanted cobaltEffect of implanta...
Conclusions                          ConclusionsFrancisco Almeida (IKS)     Doctoral dissertation   December 6, 2011   31 ...
Conclusions   Surface spin-flop in Fe/CrConclusionsSurface spin-flop in an Fe/Cr superlattice     Surface spin flop like tr...
Conclusions   Exchange bias in Fe-PtConclusionsExchange bias in Fe-Pt heterostructures     Exchange bias found in FePt/FeP...
Conclusions   Exchange bias in Co:O thin filmsConclusionsExchange bias in O implanted Co thin films     Exchange bias dete...
Conclusions   Overall conclusionConclusion    Many new research opportunities regarding these new systems:          Exchan...
Thank youFrancisco Almeida (IKS)   Doctoral dissertation   December 6, 2011   36 / 36
Upcoming SlideShare
Loading in …5
×

Public Doctoral Defense in Nuclear Physics

925 views

Published on

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
925
On SlideShare
0
From Embeds
0
Number of Embeds
12
Actions
Shares
0
Downloads
3
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Public Doctoral Defense in Nuclear Physics

  1. 1. Exchange springs and exchange bias studied with nuclear methods Francisco Miguel Cruz Sim˜es de Almeida o Instituut voor Kern-en Stralingsfysica December 6, 2011Promotors:Prof. Dr. Andr´ Vantomme eDr. Johan Meersschaut Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 1 / 36
  2. 2. OutlineMagnetism and magnetic interactions Ferromagnetism and antiferromagnetism Interlayer coupling Exchange biasResearched systems Surface spin-flop in an Fe/Cr superlattice Exchange bias in Fe-Pt heterostructures Exchange bias through ion beam synthesisConclusions Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 2 / 36
  3. 3. Magnetism and magnetic interactions Magnetism and magnetic interactionsFrancisco Almeida (IKS) Doctoral dissertation December 6, 2011 3 / 36
  4. 4. Magnetism and magnetic interactions Ferromagnetism and antiferromagnetismFerromagnetsFerromagnetic hysteresis M S 1.0 M R H 0 S 0.5 S M/M 0.0 H 0 C -0.5 -1.0 -0.2 -0.1 0.0 0.1 0.2 H (T) 0 Total magnetization (MS ). Saturation field (µ0 HS ). Remanent magnetization (MR ). Coercive field (µ0 HC ). Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 4 / 36
  5. 5. Magnetism and magnetic interactions Ferromagnetism and antiferromagnetismAntiferromagnetsAntiferromagnets have no net magnetization. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 5 / 36
  6. 6. Magnetism and magnetic interactions Ferromagnetism and antiferromagnetismMagnetic interactions Between ferromagnetic layers Interlayer exchange coupling Between a ferromagnet and an antiferromagnet Exchange bias Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 6 / 36
  7. 7. Magnetism and magnetic interactions Interlayer couplingInterlayer couplingCoupling between ferromagnetic layers separated by a spacer layer. Bilinear Biquadratic Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 7 / 36
  8. 8. Magnetism and magnetic interactions Exchange biasExchange biasExample of an oxidized cobalt thin film 1.0 0.5 (a.u.) 0.0 S M/M -0.5 -1.0 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 H (T) 0 Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 8 / 36
  9. 9. Magnetism and magnetic interactions Exchange biasExchange biasExample of an oxidized cobalt thin filmEffects observed on the hysteresis loop upon field cooling Loop shift and broadening 1.0 room temperature 10 K 0.5 (a.u.) 0.0 S M/M -0.5 -1.0 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 H (T) 0 Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 8 / 36
  10. 10. Magnetism and magnetic interactions Exchange biasExchange biasExample of an oxidized cobalt thin filmEffects observed on the hysteresis loop upon field cooling Loop shift and broadening Training 1.0 room temperature 10 K (first) 10 K (second) 0.5 (a.u.) 0.0 S M/M -0.5 -1.0 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 H (T) 0 Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 8 / 36
  11. 11. Researched systems Surface spin-flop in Fe/CrSurface spin-flop in an Fe/Cr superlatticeFrancisco Almeida (IKS) Doctoral dissertation December 6, 2011 9 / 36
  12. 12. Researched systems Surface spin-flop in Fe/CrFe/Cr superlatticeMultilayer consisting of 22 repetitions of an Fe/Cr bilayer structure ˚ Fe layers 40 A thick. Cr layers 11 ˚ thick. A Fe Cr Fe Cr Fe Cr Fe Cr Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 10 / 36
  13. 13. Researched systems Surface spin-flop in Fe/CrFe/Cr superlatticeMultilayer consisting of 22 repetitions of an Fe/Cr bilayer structure ˚ Fe layers 40 A thick and antiferromagnetically coupled. Cr layers 11 ˚ thick. A Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 10 / 36
  14. 14. Researched systems Surface spin-flop in Fe/CrFe/Cr superlatticeMagnetic response 1.0 Easy axis a 0.8 25 mT [010] H 0.6 [001] M/Ms 0.4 250 mT 0.2 0.0 1.0 Hard axis b 0.8 25 mT H 1] [0 0.6 0 1 [0 0] M/Ms 0.4 75 mT 0.2 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 µ0H (T) J. Meersschaut et al., PRB 73, 144428 (2006) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 11 / 36
  15. 15. Researched systems Surface spin-flop in Fe/CrFe/Cr superlatticeMagnetic response 1.0 Easy axis a 0.8 25 mT [010] H 0.6 [001] M/Ms 0.4 250 mT 0.2 0.0 1.0 Hard axis b 0.8 25 mT H 1] [0 0.6 0 1 [0 0] M/Ms 0.4 75 mT 0.2 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 µ0H (T) J. Meersschaut et al., PRB 73, 144428 (2006) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 11 / 36
  16. 16. Researched systems Surface spin-flop in Fe/CrSurface spin-flop (S)Transition (HC ) that causes a top spin/layer to switch orientation before theremaining spins/layers of an antiferromagnet. The irregularity propagates to the (B)middle of the spin chain, and leads to a bulk spin-flop (HC ). (S) HC : surface spin-flop field (B) HC : bulk spin-flop field Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 12 / 36
  17. 17. Researched systems Surface spin-flop in Fe/CrSurface spin-flop (S)Transition (HC ) that causes a top spin/layer to switch orientation before theremaining spins/layers of an antiferromagnet. The irregularity propagates to the (B)middle of the spin chain, and leads to a bulk spin-flop (HC ). (S) HC : surface spin-flop field (B) HC : bulk spin-flop field How to visualize a surface spin-flop? Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 12 / 36
  18. 18. Researched systems Surface spin-flop in Fe/CrPolarized Neutron ReflectometrySimilar to X-ray reflectometry. Sensitive to structural periodicity. Also sensitive to magnetic periodicity.Experiment performed in the neutron reflectometer at the HelmholtzZentrum, Berlin. ˚ Neutron wavelength λ = 4.66 A. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 13 / 36
  19. 19. Researched systems Surface spin-flop in Fe/CrPolarized Neutron ReflectometryResults μ0H = 600 mT μ0H = 200 mT μ0H = 61.8 mT μ0H = 30 mT R++ (a.u.) 0 10 -1 10 -2 10 -3 10 -4 10 0.00 0.04 0.08 0.12 0.16 0.00 0.04 0.08 0.12 0.16 0.00 0.04 0.08 0.12 0.16 0.00 0.04 0.08 0.12 0.16 -2 QZ (Å-1) QZ (Å-1) QZ (Å-1) QZ (Å-1)Γ (Å ) -41.5x10 -41.0x10 -55.0x10 0 200 400 600 800 1000 0 200 400 600 800 1000 0 200 400 600 800 1000 0 200 400 600 800 1000 Depth (Å) Depth (Å) Depth (Å) Depth (Å) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 14 / 36
  20. 20. Researched systems Surface spin-flop in Fe/CrPolarized Neutron ReflectometrySpins configuration: surface spin-flop transition ] [0 01 H 10 μ0H = 600 mT 0 [0 10 ] -1 R++ (a.u.) 10 -2 10 -3 10 -4 10 μ0H = 200 mT 0 10 -1 R++ (a.u.) 10 -2 10 -3 10 -4 10 10 0 μ0H = 61.8 mT -1 R++ (a.u.) 10 -2 10 -3 10 -4 10 μ0H = 30 mT 0 10 -1 R++ (a.u.) 10 -2 10 -3 10 -4 10 0.00 0.04 0.08 0.12 0.16 QZ (Å-1) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 15 / 36
  21. 21. Researched systems Exchange bias in Fe-Pt alloys Exchange bias in Fe-Pt heterostructuresFrancisco Almeida (IKS) Doctoral dissertation December 6, 2011 16 / 36
  22. 22. Researched systems Exchange bias in Fe-Pt alloysFe-Pt heterostructures Origin of exchange bias notoriously difficult to identify. Behavior very varied from system to system. Many models of limited applicability. Most applied techniques focus on the ferromagnet. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 17 / 36
  23. 23. Researched systems Exchange bias in Fe-Pt alloysFe-Pt heterostructures Origin of exchange bias notoriously difficult to identify. Behavior very varied from system to system. Many models of limited applicability. Most applied techniques focus on the ferromagnet. Looking into the antiferromagnet: Local information from the antiferromagnet. M¨ssbauer spectrometry of 57 Fe. o Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 17 / 36
  24. 24. Researched systems Exchange bias in Fe-Pt alloysFe-Pt heterostructures Origin of exchange bias notoriously difficult to identify. Behavior very varied from system to system. Many models of limited applicability. Most applied techniques focus on the ferromagnet. Looking into the antiferromagnet: Local information from the antiferromagnet. M¨ssbauer spectrometry of 57 Fe. o Let us take advantage of M¨ssbauer spectrometry. o Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 17 / 36
  25. 25. Researched systems Exchange bias in Fe-Pt alloys ¨Mossbauer spectrometry Source Absorber Detector γ γ v γ e- X-rays Resonant absorption of γ radiation through Doppler shift Very sensitive to small energy level shifts Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 18 / 36
  26. 26. Researched systems Exchange bias in Fe-Pt alloysFe-Pt alloys FePt3 ( Antiferromagnetic, L12 ) FePt ( Ferromagnetic, L10 ) (Fe: red spheres, Pt: white spheres) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 19 / 36
  27. 27. Researched systems Exchange bias in Fe-Pt alloysFe-Pt alloys FePt3 ( Antiferromagnetic, L12 ) Au (capping) 57 FePt 3(h) FePt (d=100 Å) MgO (110) (substrate) FePt ( Ferromagnetic, L10 ) (Fe: red spheres, Pt: white spheres) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 19 / 36
  28. 28. Researched systems Exchange bias in Fe-Pt alloysMagnetism of FePt3a) T < 160 K: Q1 wave mode, uncompensated (110) surfaceb) T < 100 K: Q2 wave mode, compensated (110) surface S. Maat et al., PRB 63, 134426 (2001) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 20 / 36
  29. 29. Researched systems Exchange bias in Fe-Pt alloysFePt/FePt3 (110) bilayersMagnetic response FePt semi-easy axis FePt hard axis 1.0 SSSSSSSSSSSSSS 1.0 SSSSSSSSSSSSSSSSS SSSSSSSSS SSSSSSSSSSSSSS SSSSSSSS SSSSSSSSSSSSS SSSSSSSSSS 0.5 0.5 SSSSSSSS M/MS (a.u.) M/MS (a.u.) SS 0.0 0.0 -0.5 FePt -0.5 FePt FePt 3 -1.0 H -1.0 FePt 3 // H -2.0 -1.0 0.0 1.0 2.0 -1.0 0.0 1.0 μ0H (T) μ0H (T) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 21 / 36
  30. 30. Researched systems Exchange bias in Fe-Pt alloysFePt/FePt3 (110) bilayersExchange bias (100 ˚ FePt/300 ˚ FePt3 ) A AObserved using a dual approach: Volume magnetization information (magnetometry). Local information (M¨ssbauer from the o 57 FePt 3 ). 400 HE 1.0 HC 0.5 M/MS (a.u.) 650000 300 0.0 μ 0HC , μ 0HE (mT) -0.5 yield (a.u.) 200 -1.0 640000 -1.0 -0.5 0.0 0.5 1.0 μ0H (T) 100 630000 0 -100 0 50 100 150 200 250 300 -1 0 1 T (K) v (mm/s) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 22 / 36
  31. 31. Researched systems Exchange bias in Fe-Pt alloysFePt/FePt3 (110) bilayersExchange bias (100 ˚ FePt/300 ˚ FePt3 ) A AWhat we observe: Very high roughness and/or intermixing. Spin-flop coupling between the FePt and the FePt3 . 400 HE 1.0 HC 0.5 M/MS (a.u.) 650000 300 0.0 μ 0HC , μ 0HE (mT) -0.5 yield (a.u.) 200 -1.0 640000 -1.0 -0.5 0.0 0.5 1.0 μ0H (T) 100 630000 0 -100 0 50 100 150 200 250 300 -1 0 1 T (K) v (mm/s) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 22 / 36
  32. 32. Researched systems Exchange bias in Fe-Pt alloysOff-stoichiometric Fe-Pt filmWhat happens if we field cool a mixture of Fe0.33 Pt0.67 ? Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 23 / 36
  33. 33. Researched systems Exchange bias in Fe-Pt alloysOff-stoichiometric Fe-Pt filmWhat happens if we field cool a mixture of Fe0.33 Pt0.67 ? 0 625000 (mT) -10 Yield (a.u.) E H 620000 0 -20 SSSSSSSSSSSSSSS 615000 -30 0 20 40 60 80 100 120 140 -5 0 5 T (K) v (mm/s) Two thirds of the sample ferromagnetically ordered at room temperature. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 23 / 36
  34. 34. Researched systems Exchange bias through ion implantation Exchange bias through ion beam synthesisFrancisco Almeida (IKS) Doctoral dissertation December 6, 2011 24 / 36
  35. 35. Researched systems Ion implantationIon implantation Ion source Target Mass separation Isotope selective technique. Control over implantation energy and amount of ions (fluence). Gaussian implantation profiles. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 25 / 36
  36. 36. Researched systems Ion implantationIon beam synthesis New method for obtaining exchange bias. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 26 / 36
  37. 37. Researched systems Ion implantationIon beam synthesis New method for obtaining exchange bias. Reactive implantation (the antiferromagnet is formed inside the ferromagnet). Extremely granular structure. Optimal contact surface. Parametric control (e.g. fluence, energy). Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 26 / 36
  38. 38. Researched systems Ion implantationIon beam synthesis New method for obtaining exchange bias. Reactive implantation (the antiferromagnet is formed inside the ferromagnet). Extremely granular structure. Optimal contact surface. Parametric control (e.g. fluence, energy). Synthesis of Cox Oy through implantation of 16 O into Co. MBE grown, capped cobalt thin films (thicknesses 600 ˚ and 1000 ˚). A A Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 26 / 36
  39. 39. Researched systems Ion implantationExchange bias in oxygen implanted cobaltExampleThin cobalt film implanted with 16 O (E = 60 keV, Φ = 1016 cm−2 ). 1.0 a) 0.5 0.0 M/M -0.5 -1.0 1.0 b) (a.u.) 0.5 0.0 S M/M -0.5 -1.0 -0.4 -0.2 0.0 0.2 0.4 H (T) 0 Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 27 / 36
  40. 40. Researched systems Ion implantationExchange bias in oxygen implanted cobaltExampleThin cobalt film implanted with 16 O (E = 60 keV, Φ = 1016 cm−2 ). 1.0 a) 0.5 0.0 M/M -0.5 -1.0 1.0 b) (a.u.) 0.5 0.0 S M/M -0.5 -1.0 -0.4 -0.2 0.0 0.2 0.4 H (T) 0 How to interprete this magnetic response data? Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 27 / 36
  41. 41. Researched systems Ion implantationExchange bias in oxygen implanted cobaltLoop shape analysis μ0HE μ(x) y = r-rμ μ+3σ rμ rmax μ μ-3σ rmin μ-3σ μ μ+3σ μ0HC xQuantify the hysteresis loop shape based on statistics. Use a gaussian distributions for the quantities as an approximation. Mean and variance of exchange bias. Mean and variance of coercivity. This gaussian is associated to the implantation profile. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 28 / 36
  42. 42. Researched systems Ion implantationExchange bias in oxygen implanted cobaltEffect of implantation energy on the exchange bias 1.0 E = 30 keV E = 45 keV 0.5 S 0.0 M/M -0.5 -1.0 -0.30 -0.15 0.00 0.15 0.30 H (T) 0 Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 29 / 36
  43. 43. Researched systems Ion implantationExchange bias in oxygen implanted cobaltEffect of implantation energy on the exchange bias 120 40 E = 30 keV E = 30 keV E = 45 keV E = 45 keV 90 30 (mT) (mT) C H C 0 H 60 20 0 Variance Mean 30 10 0 0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 25 15 E = 30 keV E = 30 keV E = 45 keV E = 45 keV 20 (mT) (mT) 10 15 E H E 0 H 0 Variance 10 Mean 5 5 0 0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 T (K) T (K) Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 30 / 36
  44. 44. Conclusions ConclusionsFrancisco Almeida (IKS) Doctoral dissertation December 6, 2011 31 / 36
  45. 45. Conclusions Surface spin-flop in Fe/CrConclusionsSurface spin-flop in an Fe/Cr superlattice Surface spin flop like transition detected in a biaxial Fe/Cr superlattice, along the hard axis. Demonstrated through Polarized Neutron Reflectometry. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 32 / 36
  46. 46. Conclusions Exchange bias in Fe-PtConclusionsExchange bias in Fe-Pt heterostructures Exchange bias found in FePt/FePt3 bilayers. FePt easy axis orthogonal to FePt3 easy axis (spin-flop coupling). Local information extracted from the antiferromagnet via M¨ssbauer o spectrometry. Exchange bias detected in a single layer of disordered off-stoichiometric Fe-Pt. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 33 / 36
  47. 47. Conclusions Exchange bias in Co:O thin filmsConclusionsExchange bias in O implanted Co thin films Exchange bias detected in oxygen implanted Co thin films. New kind of exchange biased system. Antiferromagnet is embedded in the ferromagnet. Heterogeneous effect. Requires a fluence of the order of at least Φ = 1016 cm−2 . The effect is sensitive to the fluence as well as the implantation energy. Post implantation annealing enhances and homogenizes the obtained effect. Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 34 / 36
  48. 48. Conclusions Overall conclusionConclusion Many new research opportunities regarding these new systems: Exchange bias between Fe-Pt alloys presents new challenges. Evident direction for further research. M¨ssbauer techniques give us more flexibility. o Exchange bias obtained via ion implantation opens a new field of research: Principle may be applied to many other systems besides Co/CoO. Wealth of technological applications (e.g. patterned implantation). Theoretical challenge: transition from 2D systems (bilayers) to 3D systems (implanted films, fully granular structures). Francisco Almeida (IKS) Doctoral dissertation December 6, 2011 35 / 36
  49. 49. Thank youFrancisco Almeida (IKS) Doctoral dissertation December 6, 2011 36 / 36

×