Giant magneto resistivity in Fe 3-x Zn x O 4 nanowire structures 産研 田中研 尾野 篤志

Contents Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn) 3 O 4 ―Fabrication method of nanostructures Purpose Experiments and results Conclusion

Contents Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn) 3 O 4 ―Fabrication method of nanostructures Purpose Experiments and results Conclusion

Coulomb interaction U ～ 5eV ■ This important system is studied with keen interest all over the world. VO2VO2 YBa 2 Cu 3 O 7 (La,Ca)MnO 3 Electric crystal Metal-insulator transition Ferromagnetism at high temperature ・ Giant magneto resistance Ferromagnetism at high temperature ・ Giant magneto resistance Insulator ・ Anti-ferromagnetism Insulator ・ Anti-ferromagnetism MeltingMelting Super conductivity at high temperature Introduction strongly correlated electron system

VO 2 LPCMO Introduction strongly correlated electron systems in nanoscale 100nm M. Fäth et al, Science 285 (1999)1540 Ferromagnetic Anti-Ferromagnetic M. M. Qazilbash et al, Science 318 (2007) 1750, Metal Insulator (La, Pr,Ca)MnO 3 film STM image VO 2 film SNIM image 500nm Different domains exist separately each other. Domain size is ~ a few hundred nm

500nm Introduction strongly correlated electron systems in nanoscale InsulatorMetal Y. Yanagisawa et al Appl. PHYSICS LETTERS 89 (2006) (La, Pr,Ca)MnO 3 Nanostructure of domain scale show new physical properties? Enormous Magneto Resistive effect was observed in nanosize.

Introduction strongly correlated electron systemsin nanoscale 500nm (La, Pr,Ca)MnO 3 film Charge Ordering Insulator Ferromagnetic metal 1μm Change of MRgraduallysuddenly

Contents Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn) 3 O 4 ―Fabrication method of nanostructures Purpose Experiments and results Conclusion

Introduction Fe 3 O 4 and Fe 3-x Zn x O 4 Fe 3 O 4 Ferrimagnetic RT A site: Fe 3+ B site: Fe 2+, Fe 3+ A-Bsite: Super-exchange interaction ⇒ Anti-ferromagnetic coupling B-Bsite: Double-exchange interaction ⇒ Metallic conductivity Fe 3+ In A-site is substituted with Zn 2+ Control of super exchange interaction → Magnetisation increase Decrease of Fe 2+ (Carrier) → Semiconductor Fe 3-X Zn x O 4 :

Introduction Property of Fe 3-x Zn x O 4 At Room temperature Ferromagnetism Semiconductor Spinel structure Earth-friendly material (Fe, Zn) Candidate of spintronics devices

Contents Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn) 3 O 4 ―Fabrication method of nanostructures Purpose Experiments and results Conclusion

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

Top down ： ○High controllability of size, position, and form ×More advanced technique is required to fabricate more precise structure Introduction Top down technique and Bottom up technique 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 few Å ) ×There is a difficulty in controlling size, position, and shape Ex.) Pulsed Laser Deposition, MOCVD, etc

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

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

Contents Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn) 3 O 4 ―Fabrication method of nanostructures Purpose Experiments and results Conclusion

Purpose Y. Yanagisawa et al Appl. PHYSICS LETTERS 89 (2006) (La, Pr,Ca)MnO 3 film at 10K GMR was observed 500nm 45nm ZnO Fabrication method was established

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

Contents Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn) 3 O 4 ―Fabrication method of nanostructures Purpose Experiments and results Conclusion

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

Experimental method Fabrication of FZO nanowire utilizing sidewall growth Utilizing sidewall growth (Horizontal growth can be controlled) FZO Sidewall growth substrate Organic resist Bottom up

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

Experiment 1-1. Control thickness of FZO sidewall Film thickness ∝ Sidewall thickness Film thickness ∝ time Sidewall thickness can be controlled by changing deposition time Deposition on plain substrate Deposition time [min.] Film’s thickness [nm] Measurement: AFM Temperature: RT Substrate: MgO(001) P O2 : 1x10 -2 Pa Deposition time: min. T=1.14t T: Film’s thickness t: deposition time

Experiment 1-2. Searching for crystallizing condition of FZO Peak of (111)-oriented FZO was observed. Crystallization of FZO was succeeded by annealing. Temperature : 600 ~ 800 ℃ P O2 : 1×10 -4 ~ 1×10 -1 Pa Annealing time: 5hrs. Substrate: Al2O3

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

Contents Introduction ―Strongly correlated electron systems in nanoscale ―Property of (Fe, Zn) 3 O 4 ―Fabrication method of nanostructures Purpose Experiments and results 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 Al 2 O 3 was optimized.

Experimental method Fabrication of FZO nanowire utilizing sidewall growth

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

FZO の結晶化条件の模索 on MgO substrate MgO 基板でピーク見えず Al 2 O 3 (0001) 基板に変更 MgO substrate 800 ℃ anneal Intensity (a.u.)

Experiment 1. Deposition on plain substrate Control of sidewall thickness Crystallization method Experiment on plain substrate 1-1. Control thin film’s thickness 2-2. Optimize crystallization condition by annealing Measurement: 1. AFM :2. XRD Substrate: MgO(001) P O2 : 1x10 -2 Pa Temperature: RT Deposition time: min. Temperature : 600 ~ 800 ℃ P O2 : 1×10 -4 ~ 1×10 -1 Pa Annealing time: 5hrs. Should be learned.

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

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

Experiment Establishing 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 Zn O 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