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Spin Dynamics of Free Exciton Magnetic Polarons in Bulk Cd 1-x Mn x Te

Spin Dynamics of Free Exciton Magnetic Polarons in Bulk Cd 1-x Mn x Te. Y. Hashimoto H. Mino, T. Yamamuro, D. Kanbara, T. Matsusue Chiba University, Japan S. Takeyama Tokyo University, Japan. Outline 1. What is free exciton magnetic polaron ? 2. Sample 3. Results & Discussion

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Spin Dynamics of Free Exciton Magnetic Polarons in Bulk Cd 1-x Mn x Te

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  1. Spin Dynamics of Free Exciton Magnetic Polarons in Bulk Cd1-xMnxTe Y. Hashimoto H. Mino, T. Yamamuro, D. Kanbara, T. Matsusue Chiba University, Japan S. Takeyama Tokyo University, Japan Outline 1. What is free exciton magnetic polaron ? 2. Sample 3. Results & Discussion PL & absorption Photo-induced Faraday rotation 4. Conclusions

  2. Magnetic Polaron Mn spin h e Exciton spin Localization only by sp-d exchange interaction h e Free Exciton Magnetic Polaron (FEMP) A Golnic, et. al. J. Phys. C16, 6073 (1983) M. Umehara, Phys. Rev. B 68, 193202 (2003) Bound Magnetic Polaron (BMP) Local magnetic order surrounding an impurity bound exciton E impurity

  3. What is interesting about FEMP ? FEMP Circular polarized light Photo-induced magnetism via the FEMP BMP Circular polarized light No magnetism via the BMP

  4. Localization energy 5 10 Mn Concentration [%] x = 5 ~ 10% → FEMP energy : Large Alloy potential fluctuation : small Free exciton magnetic polaron (FEMP) in CdMnTe Localization energy of Magnetic Polaron Alloy Potential fluctuation S. Takeyama, J. of Crys. Growth, 184-185 (1998) 917-920 Current work : High quality CdMnTe sample with low Mn concentration Photoluminescence Photo-induced Faraday rotation (PIFR)

  5. Sample Bulk Cd1-xMnxTe x = 5% GaAs substrate Transparent buffer layer Cd1-yMgyTe Cd0.95Mn0.05Te Quartz disk The opaque GaAs substrate was removed. CdMgTe layer is transparent in the wavelength of CdMnTe’s resonance.

  6. Absorption and Photoluminescence Absorption: 4.2 K, PL: 1.4K PL Light source：He-Ne 633nm Absorption Photoluminescence Photon energy [eV] Distinct PL line of the FEMP appear !! FEMP binding energy  1.8 meV

  7. Experimental setup of PIFR Time Delay 76MHz Ti:Sapphire Laser B.S. λ/2 λ/4 Probe Pump λ/2 FX absorption Laser spectrum Sample 1.4 ~ 300K 0 ~ 6.9T Lock-in Amplifier Polarization Beam Splitter Optical Bridge

  8. Spin dynamics in CdMnTe Long decay process > Pulse separation of the Ti:S laser: 13ns Mn spin relaxation ≈100ns T. Strutz et.al, Phys. Rev. Lett 68, 3912 (1992) < 1 ps : Hole spin 1.4K s+ s- 8 ps : Electron spin Ferromagnetic spin alignment of the Mn ions via the FEMP !!!

  9. Summary • Performed first time-resolved Faraday rotation on CdMnTe which shows clear FEMP PL • Spin dynamics of holes, electrons and Mn ions • tspin (hole) < 1 ps • tspin (electron) ~ 8 ps • tspin (Mn) > 13 ns • Possible evidence of photo-induced magnetism via FEMP formation

  10. Temperature dependence of the PL spectra FXMP FX 1.4K 25K

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