Study of Ferromagnetism of Diluted Magnetic Semiconductor Zn 1-x Cr x Te with MCD

1. Study of Ferromagnetism of Diluted Magnetic SemiconductorZn1-xCrxTe with MCD [Referenece] H.Saito,V.Zayets,S.Yamagata,and K.Ando Phys.Rev.Lett. 90,207202(2003) ITOH Lab. Yoshitaka Sakamoto (坂本　圭隆)

2. Contents Introduction 　　・Abstract 　　・Background of reference 　　・How MCD is used in the reference Main talk 　　・What is MCD 　　・MCD spectroscopy 　　・Method ,result ,analysis (in the reference) Summary

3. Abstract I’ll explain about… MCD Magnetic Circular Dichroism 磁気　　　　　　 　円　　　　　　　　二色性 Reference source: “Zn1-xCrxTe” made in AIST (産業技術総合研究所)

4. [Ref.1] H.Saito,V.Zayets,S.Yamagata,and K.Ando Phys.Rev.Lett. 90,207202(2003) Background of the reference 希　釈　磁　性　半　導　体　 DMS=Diluted Magnetic Semiconductor ⇒ Ga1-xMnxAs,In1-xMnxAs etc…

5. I can’t wait any more… Magnetism Electronics Optics [Ref.2] http://www.nanoelectronics.jp MCD use in the article problem of DMS ・need magnetism in room temperature　→ Zn1-xCrxTe ・to know what the magnetism causes　→ MCD is useful

6. CrTe Zn1-xCrxTe ZnTe CrTe CrTe comparing MCD spectra between ZnTe and CrTe and ZnCrTe The problem of Zn1-xCrxTe 強　磁　性 Where does the Ferromagnetism come from? sp-d exchange interaction direct interaction (CrTe cluster)

7. SQUID(=Superconducting Quantum interference device :超伝導量子干渉計) It can determine the magnetization of a substance by searching the changes of the magnetic bunch which through the substance. H-M curve can be made. But we cannot get the information of electron states. MCD(=Magnetic Circular dichroism :磁気円二色性) We can see the difference of absorption between right circular polarization and left circular polarization. And we can determine the energy of Zeeman’s splitting, permittivity, magnetization and so on. We are able to observe the excitation of electrons. Measurement method in the reference

8. I0：input light intensity σ±: right (left) circular light T±: transmissivity Field I±: penetrating intensity σ＋ I＋ I0 T+ Field σ－ I－ I0 T－ What is MCD? Difference of transmission between two Circular Polarizations 円　 偏光　

9. → ^ E(t) = Eoexp(-iωt) x → ^ E(t) = E1 exp(-iωt) x +E2 Eoexp(-iωt)y ^ How’s the light? = electromagnetic wave, which result in the vibration of a lot of oscillators x z <<<<Linearly Polarization y x z <<<<Elliptical Polarization y

10. → ^ ^ E(t) = ½Eoexp(-iωt) (x+iy) + ½Eoexp(-iωt) (x-iy) ^ ^ → ^ E(t) = E1 exp(-iωt) x +E2 exp(-iωt)y → ^ ^ E(t) = ½(E1+E2)exp(-iωt) (x+iy) + ½(E1-E2)exp(-iωt) (x-iy) ^ ^ ^ Circular polarized light is… x Linearly Polarization>>>> → ^ E(t) = Eoexp(-iωt) x ⇔ y Elliptical Polarization>>>>> x ⇔ y

11. Right Circular Polarization (右円偏光) ：σ+ = 1 Left Circular Polarization (左円偏光) ：σ- = -1 Angular momentum The two (right and left) circular light that one has the same energy as the other differs the angular momentum each other that influences to electrons (or atoms). J=3/2 So… for example: RCP is able to be absorbed LCP is not absorbed J=1/2

12. Absorption difference on ZnTe J=1/2 Conduction band J= - 1/2 Conservation law of Angular momentum σ+ ：+1σ－：- 1 σ- σ+ E-=Eg-μBH E+=Eg+μBH J=3/2 J= -3/2 Valence band

13. How to measure Polarizer(b) (not parallel to (a)) PEM monochrometer (分光器) (Photo Elastic Modulator) target light source photo multiplier (光電子増倍管) Polarizer(a) Lock-in amp.

14. Absorption coefficient α+ α- E- E+ Energy α-－α+ E+ E- Energy Predictable signal I+=(1-α+ζ)Io+ I-=(1-α-ζ)Io-

15. R = R+ + R- r = R+ - R- Calculation N±=n±+iκ± N: complex refractive indexn: refractive index κ: extinction coefficient 屈折率　 複屈折率　 消光係数 α±=2ωκ±/c α: absorption coefficientω: frequency c: speed of light 吸収係数　 周波数 光速 ηF=ωΔκ/2c (=r /R) ηF: Faraday elliptical index r ファラデー楕円率 R

16. Valuable graph ηF= tanηθ ηθ：angle of elliptical coefficient 楕円率角　 almost all the cases ηθ<<1, so, ηF≒ηθ RCP is less absorbed than LCP ηθ(deg/cm) 0 Energy (eV) LCP is less absorbed than RCP

17. Result and Analysis (a) CrTe film at room temp. (b) ZnTe film (c) Zn1-xCrxTe(x=0.20) 80nm film at 20K (d) Zn1-xCrxTe(x=0.20) 400nm film at 20K L-CP ： symmetrical point in brillouin zone Γ-CP: center of k-space “sp-d exchange interaction” may causes the ferromagnetism☆

18. Summary ・As far as we see MCD spectra, CrTe cluster isn’t a factor of the ferromagnetism of ZnCrTe and the spectrum of ZnCrTe similar to that of ZnTe. It implies that the ferromagnetism comes from sp-d exchange interaction. ・I think the analysis becomes more sophisticated when the permittivity and magnetization are calculated. ・We cannot do the pico or femto second time-resolved measurement but by using LIGHT. It’ll disclose the excitation state more clearly. Such MCD spectroscopy is the plan for my reserch.

20. Field H 2gμBH Physical point of view Zeeman’s splitting(ゼーマン分裂) ・Magnetic semiconductor： RKKY interaction (RKKY相互作用) or ・Ferromagnet： Domain wall(磁区) permittivity(誘電率) and magnetization(磁化率)

21. domain wall sp-d interaction Application nonvolatile memory (不揮発性メモリ) with very large storage!

22. H RKKY interaction localized electron doped by Cr Itinerant electron (遍歴電子) localized electron doped by Cr Notsameas Ferromagnet!!

23. ?Diluted :x<=0.20　多すぎるとFerromagnet を形成。 AIST National Institute of Advanced Industrial Science and Technology. ③ZnCrTeの結晶構造はどうなるか。 Zn： 30番4周期12族d電子持ち[3d(10)4s(2)]、反磁性体 六法細密構造、135pm Te： 52番5周期16族p電子持ち[4d(10)5s(2)5p(4)]、非磁性体 六方晶構造、140pm Cr： 24番4周期6族d電子持ち[3d(5)4s(1)]、強磁性体 体心立方格子、140pm アクセプターとして働く。 ZnTe： バンドギャップ＝2.39eV at 0K(約520nm(GaAsは830nm,InAsは3000nm)) 格子定数＝6.103Å 赤みがかった透明。赤褐色

24. XRD(=X-ray diffraction :X線回折) It is used to check the crystal structure. And we can know the local gradient of it. RHEED(=reflection high-energy electron diffraction :反射高速電子回折) We are able to get the crystal structure and direction of growth by analyzing the diffraction pattern. And can get the information how the substance surface is flat from the spot shape.