Giant magneto resistivity in Fe 3-x Zn x O 4 nanowire structures

1. Giant magneto resistivity in Fe3-xZnxO4 nanowire structures 産研　田中研 　尾野 篤志

2. Contents • Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn)3O4 ―Fabrication method of nanostructures • Purpose • Experiments and results • Conclusion

3. Contents • Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn)3O4 ―Fabrication method of nanostructures • Purpose • Experiments and results • Conclusion

4. Introductionstrongly correlated electron system Ferromagnetism at high temperature ・Giant magneto resistance Coulomb interactionU～5eV (La,Ca)MnO3 Electric crystal Melting Metal-insulator transition VO2 Insulator・ Anti-ferromagnetism Super conductivity at high temperature YBa2Cu3O7 ■This important system is studied with keen interest all over the world.

5. Introductionstrongly correlated electron systems in nanoscale 100nm 100nm 100nm 100nm 100nm Different domains exist separately each other. (La, Pr,Ca)MnO3 film STM image VO2 film SNIM image LPCMO VO2 Metal Ferromagnetic Insulator Anti-Ferromagnetic 500nm M. Fäth et al, Science 285 (1999)1540 M. M. Qazilbashet al, Science 318 (2007) 1750, Domain size is ~ a few hundred nm

6. Introductionstrongly correlated electron systemsin nanoscale Nanostructure of domain scale show new physical properties? Insulator Metal (La, Pr,Ca)MnO3 500nm Y. Yanagisawaet al Appl. PHYSICS LETTERS 89 (2006)253121 EnormousMagneto Resistive effect was observed in nanosize.

7. Introductionstrongly correlated electron systemsinnanoscale Charge Ordering InsulatorFerromagnetic metal (La, Pr,Ca)MnO3 film 1μm 500nm Change of MR gradually suddenly

8. Contents • Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn)3O4 ―Fabrication method of nanostructures • Purpose • Experiments and results • Conclusion

9. IntroductionFe3O4 and Fe3-xZnxO4 Fe3O4Ferrimagneticmetal @ RT A site: Fe3+ B site: Fe2+, Fe3+ A-Bsite: Super-exchange interaction 　　　　⇒Anti-ferromagnetic coupling B-Bsite: Double-exchange interaction ⇒Metallic conductivity Fe3+ eg t2g JA-B A-site Fe3+ Fe2+ JB-B eg B-site t2g Carrier • Fe3+ In A-site is substituted with Zn2+ • Control of super exchange interaction • → Magnetisation increase • Decrease of Fe2+ (Carrier) • → Semiconductor Fe3-XZnxO4:

10. IntroductionProperty of Fe3-xZnxO4 • At Room temperature • Ferromagnetism • Semiconductor • Spinel structure • Earth-friendly material (Fe, Zn) • Candidate of spintronics devices

11. Contents • Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn)3O4 ―Fabrication method of nanostructures • Purpose • Experiments and results • Conclusion

12. IntroductionHow to fabricate nanostructures AFM Lithography MR was observed Difficulty in controlling fine size Degradation of reproducibility We need to fabricate smaller structure than ever… General fabrication technique of oxide nanostructure is required

13. Introduction Top down technique and Bottom up technique Top down： ○High controllability of size, position, and form ×More advancedtechnique is required to fabricate more precise structure Ex.) Nano Imprint Lithography, AFM Lithography, e-Beam Lithography, etc Bottom up： ○Size of thin film can be controlled in the atomic layer scale (a fewÅ) ×There is a difficulty in controlling size, position, and shape Ex.) Pulsed Laser Deposition, MOCVD, etc

14. Introduction Combination of Top down and Bottom up Combination of Top down and Bottom up ○High controllability of size, shape, and position ○Structures with the atomic layer size can be fabricated Nano Imprint Lithography Pulsed Laser Deposition

15. Introduction Fabrication of ZnO nanobox Polymers on substrate ZnO-deposited substrate 45nm 1μm 500nm Ion Milling Acetone cleaning 1μm 1μm

16. Contents • Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn)3O4 ―Fabrication method of nanostructures • Purpose • Experiments and results • Conclusion

17. Purpose (La, Pr,Ca)MnO3 film ZnO at 10K 45nm 500nm Y. Yanagisawaet al Appl. PHYSICS LETTERS 89 (2006)253121 GMR wasobserved Fabrication method was established

18. Purpose Next purpose Fabrication of FZO nanowire by utilizing sidewall growth Emergency of GMR at Room temperature Application of FZO nanowire to spintronics devices

19. Contents • Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn)3O4 ―Fabrication method of nanostructures • Purpose • Experiments and results • Conclusion

20. Experimental methodFabrication of FZO nanowire utilizing sidewall growth Size and position can be controlled by the array of resist pattern Mold Top down (NIL) Regist Substrate

21. Experimental methodFabrication of FZO nanowire utilizing sidewall growth Utilizing sidewall growth (Horizontal growth can be controlled) Organic resist FZO Bottom up (PLD) @RT substrate Sidewall growth

22. Experimental method • Deposition on Plane Substrate 1-1. Control thin film’s thickness 1-2. Optimize crystallization condition by annealing • Deposition on Nano-patterned substrate ― Fabricate FZO nanowire using sidewall growth Deposition@ Room temperature

23. Experiment 1-1.Control thickness of FZO sidewall Deposition on plain substrate Measurement: AFM Temperature: RT Substrate: MgO(001) PO2: 1x10-2 Pa Deposition time: 30-90 min. • Sidewall thickness can be controlled by changing deposition time Film’s thickness [nm] T=1.14t T: Film’s thickness t: deposition time Film thickness∝Sidewall thickness Film thickness ∝　time Deposition time [min.]

24. Experiment 1-2.Searching for crystallizing condition of FZO Substrate: Al2O3 Temperature : 600 ~ 800℃ PO2: 1×10-4~ 1×10-1Pa Annealing time: 5hrs. Substrate: Al2O3 Peak of (111)-oriented FZO was observed. Crystallization of FZO was succeeded by annealing.

25. Experiment 2.FZO nanowire • I am trying to fabricate FZO nanowire. • Finally, I will measure the MR and apply it to spintronics devices.

26. Contents • Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn)3O4 ―Fabrication method of nanostructures • Purpose • Experiments and results • Conclusion

27. Conclusion • I am trying to fabricate FZO nanowire. • The nanostructure fabrication technique: combination of Top-down and Bottom-up process utilizing sidewall growth was suggested. • Time-dependency of FZO-thin-film’s thickness is observed. • Crystallization condition of FZO on Al2O3 was optimized.

30. Experimental methodFabrication of FZO nanowire utilizing sidewall growth

31. Searching for crystallizing condition of FZO 600℃, Po2 = 1×10-3 mbar 700℃, Po2 = 1×10-4 mbar Intensity (a.u.) 2θ(°) Peak of FZO (111)-oriented was observed.

32. FZOの結晶化条件の模索on MgO substrate MgO基板でピーク見えず Intensity (a.u.) MgO substrate 800℃ anneal Al2O3 (0001) 基板に変更

33. Experiment1. Deposition on plain substrate Experiment on plain substrate 1-1. Control thin film’s thickness 2-2. Optimize crystallization condition by annealing Measurement: 1. AFM :2. XRD Should be learned. • Control of sidewall thickness • Crystallization method Substrate: MgO(001)PO2: 1x10-2Pa Temperature: RTDeposition time: 30-90 min. Temperature : 600 ~ 800℃ 　 PO2: 1×10-4~ 1×10-1Pa Annealing time: 5hrs.

34. Experiment 1-2.Searching for crystallizing condition of FZO Crystallized FZO can be prepared by annealing.

35. Seeking growth condition for fabricating FZO nanowire Optimization of the condition Crystallizing condition of ZnO: Crystallize by annealing 評価:XRD(結晶状態の分析) • Method of crystallization 結晶化温度: 550°,950° 加熱時間　 :5hrs. ,6hrs.

36. ExperimentEstablishing the fabrication technique of oxide nanostructures by combining Top down and Bottom up At first • Making a prototype by ZnO • Establishing the fabricating process • Making sure accuracy and reproducibility • Measuring the physical properties • ZnO • Oxide semiconductor • Eg=3.37V • It is easy to grow on any substrates at room temperature • It can be c-axis oriented crystal at room temperature • Zn • O