Drickamer type. Disk containing the specimen. Pressure cell. Press

Transcription

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2 ε-fe

3 Drickamer type Press Pressure cell Disk containing the specimen

4 Low Temperature Cryostat

5 Diamond Anvil Cell (DAC) Ruby manometry Re gasket for collimation Small size of specimen space High-density source Fe 57 enriched specimens

6 High-Pressure Mössbauer Experiments γ K

7 Direction of the γ-ray source Ferro. 2 nd & 5 th line intensities become zero DAC Antiferro. 2 nd & 5 th line intensities increase

8 cryostat External magnetic fields: 1-7 T

9 Mössbauer spectra of Pd-2%Fe alloy vs. 57 Co in Rh source under various applied fields T Relative Transmission T 3 T T 7 T Velocity, v / mm s

10 SrFeO 3 La 1/3 Sr 2/3 FeO 3 CaFeO 3

11 SrFeO 3 Cubic perovskite structure High valence state: Fe +4 T N = 134 K screw spin str. No charge disproportionation Metallic conductivity to 4 K FeO 6 Octa. :Sr :O :Fe

12 ö

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14 74 GPa 300 K Antiferro. Ferro.

15 Results from SrFeO3

16 Summary (SrFeO 3 ) Relative Transmision Velocity, v / mm s GPa 4.5 K 10 Transition from screw spin structure to collinear ferro. at about 7.2 GPa. Phase diagram of SrFeO 3

17 LaSr2Fe3O9

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21 Summary (Perovskite) High-pressure 57 Fe Mössbauer measurements at 4.5 K under external magnetic fields up to 7 T have been performed perovskite iron oxides using a DAC and superconducting magnet. Pressure induced ferromagnetism. Most probably due to the double exchange interaction. Ground states of these oxides switch to uniformcharge and ferromagnetic states under external high pressure.

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23 Nuclear Excitation & Nuclear Resonant Scattering with Synchrotron Radiation Elastic scattering Hyperfine interaction spectroscopy Ultra-monochromatic X-ray Inelastic scattering Phonon density of state Γ - t - / 1 2 -i t ie0t h h ψ () t = ψ(0) e e = dωg( ω) e ω 2π Frequency Domain Time Domain 1 ih g( ω) = 2 ψ(0) π ( ) iγ ωh E0 + 2

24 How to get Nuclear Scattered Photons Forbidden reflections for the electronic Thomson Scattering by using an antiferromagnetic singlecrystal Time-delay of Nuclear Scattering GIAR(Grazing Incidence Anti-reflection) Film

25 Coherent scattering : Coherent excitation & Coherent deexcitation Quantum Beat

26 Quantum Beat in Time Spectrum

27 Linear Polarization of SR

28 SR Diamond Anvil Cell

29 Collective excitation of nuclei (nuclear exciton) Collective de-exciation A = P N n A ij j =1 i =1 N i=1 n A ij j =1 2 I(t) N 1 e iω 1 t +N 2 e iω 2 t 2 e t/τ =(N 12 +N 22 ) e t/τ +2N 1 N 2 e t/τ cos(ω 1 ω 2 )t

30 Time integral forward scattered intensity I fs 0 * (t)dt = E fs (t)e fs (t)dt 0 = 1 E 2π fs (ω)e * fs (ω)dω E fs (ω) is the Fourier transform of E fs (t). Transmission amplitude E tr = E i e iλf 0 ρ z f 0 (ω) = k 8π σ Γ / h 0 χf LM ω ω 0 iγ /2h f σ, σ (ω) = k 8π σ 0χf LM n Γ / h j =1 ω ω 0 iγ /2h C 2 (1) (1)* ( j e,1, j g ;m e, m j,m g )D m j,σ (0,θ,φ)D m j, σ (0,θ,φ)

31 Nuclear Resonant Scattering (NRS) Scatterer = Nucleus of one specific isotope ( 40 K, 57 Fe, 83 Kr, 119 Sn, 121 Sb, 149 Sm, 151 Eu, 161 Dy, 169 Tm, 181 Ta) Elastic scattering: Local magnetic and electric information 57 Fe

32 Nuclear Resonant Scattering (NRS) Scatterer = Nucleus of one specific isotope ( 40 K, 57 Fe, 83 Kr, 119 Sn, 121 Sb, 149 Sm, 151 Eu, 161 Dy, 169 Tm, 181 Ta) Elastic scattering: Local magnetic and electric information intensity 57 Fe time

33 Nuclear Resonant Scattering (NRS) Scatterer = Nucleus of one specific isotope ( 40 K, 57 Fe, 83 Kr, 119 Sn, 121 Sb, 149 Sm, 151 Eu, 161 Dy, 169 Tm, 181 Ta) Elastic scattering: Local magnetic and electric information 57 Fe

34 Nuclear Resonant Scattering (NRS) Scatterer = Nucleus of one specific isotope ( 40 K, 57 Fe, 83 Kr, 119 Sn, 121 Sb, 149 Sm, 151 Eu, 161 Dy, 169 Tm, 181 Ta) Elastic scattering: Local magnetic and electric information 57 Fe

35 Beating beating appears if two signals with a slightly different frequency are added beating frequency = difference in frequency of both signals + = + =

36 Nuclear Resonant Scattering (NRS) Scatterer = Nucleus of one specific isotope ( 40 K, 57 Fe, 83 Kr, 119 Sn, 121 Sb, 149 Sm, 151 Eu, 161 Dy, 169 Tm, 181 Ta) Elastic scattering: Local magnetic and electric information Intensity (log-scale) 57 Fe Time (ns)

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39 ε-fe

40 High-pressure phase of iron, ε-fe Structure transition from α-fe to ε-fe at 13 GPa ε-fe does not show any magnetic order even at K Rf. Cort et al. J. Appl. Phys. 53, 2064 (1982). Band structure calculation suggests that ε-fe is Pauli paramagnet. Rf. Fletcher and Addis, J. Phys. Metal Phys. 4, 1951 (1974). Discovery of superconductivity in ε-fe Rf. K. Shimizu et al., Nature 412, 316 (2001).

41 Superconductivity in ε-fe K. Shimizu et al., Nature 412, 316 (2001).

42 57 Fe Mössbauer M spectra of iron at 298 K under various pressures Relative Transmission MPa 4 GPa 10 GPa 13 GPa Velocity, v / mm s GPa

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44 57 Fe Mössbauer M spectra of ε-fe at 20 GPa and 4.5 K under applied fields Relative Transmisson T 1T 3T 5T 7T C. S., δ / mm s -1 Hyperfine Field, H int. / T External Field, H ext. / T Velocity, v / mm s -1

45 Summary (ε-fe) High pressure 57 Fe Mössbauer measurements have been performed for ε- Fe at 4.5 K and 20 GPa using DAC with radioactive source 57 Co in Rh under longitudinally applied external magnetic fields up to 7 T. No induced hyperfine magnetic fields at 57 Fe in ε-fe suggesting that ε-fe has no local moment.

46 E N D

47 10-9 ev 10-7 ev (Hyperfine interaction spectroscopy) Magnetic dipole moment vs Magnetic fields Local magnetic moments

48 (Hyperfine interaction spectroscopy)

49 Mössbauer spectroscopy High Pressure Apparatus Drickamer Type Diamond Anvil Cell

50 Gamma-Decay of the Nucleus hω i = α ; j, m, L, M, π π e e e f = β ; j, m, π g g g Energy : E i = E f + Angular momentum: Parity : π e = π g π π e π g =(-1) L Electric 2 L pole (EL) radiation π e π g =(-1) L-1 Magnetic 2 L pole (ML) radiation hω j j L j + j, L 0 e g e g M = m m L π e π g =1: no parity change π e π g =-1: parity change γ-ray (photon): wave vector k, polarization ξ ξ=+1 right-handed circular polarization ξ= 1 left-handed circular polarization e g ξ=+1 ξ= 1 k

51 ,, jg mg π g je, me, π e γ k, ξ C W( k, ξ; m, m ) = j mπ C H j m π C e g e e e int g g g 1 = [ ()] = ( ) ( ) ' Hint H R l j Ri A Ri c i 1/2 2π c A( R) (, ) ˆ(, )exp{ [ ( ) ]} i = h a k ξ e k ξ ik R l ri CC k, ξ kv ( ξ ) a k, : ek ˆ(, ξ ) W j mπ H j m π C e C e ' ik u( l) ik R 0 () l e e e g g g T T absorption emission transition matrix for a free nucleus 2 probability amplitude for recoilless 3 phase factor for interatomic interference effects Recoilless fraction ik u () l f( k, T) C e C T 2

52 2 ( Γ /2) σ = fσωf ( θ) ( ) ( /2) σ 0 0 i i 2 2 hωk + Eg Ee + Γ ik u () l f C e C 2 1 2je = 2π k 2j α ( θ) = ( + ) ξ =± 1 2 T L jg L je ωi = M= L mg M m e L f 2L 1 D ξ ( φθ0) i = g M T 2 2

53 Mössbauer spectrometer

54 Mössbauer spectrometer 2

55 SPring-8

56 Beamline Map at SPring-8

57 Nuclear Resonant Scattering: two identical single line samples, one with variable velocity ω ω excited r v Counts Detector ω ground Time

58 Stroboscopic Detection v r Normalized intensity Prompt pulses ω ω sample Time-windows Time

59 Stroboscopic Detection Eu 2 O 3 -Eu 2 O 3 V=4.82mm/s V=14.46mm/s time (ns)

60 Stroboscopic Detection 151 Eu in Eu 2 O 3 V=2.41mm/s V=4.82mm/s V=7.23mm/s V=9.64mm/s V=12.05mm/s V=14.46mm/s time (ns)

61 Isomer shift determination: Pressure dependence of the isomer shift of 151 Eu in EuPd 2 Si 2 Eu 2+ : (Xe) 4f 7 5d 0 6s 0 Eu 3+ : (Xe) 4f 6 5d 0 6s 0 DI Valence fluctuations: 7th elektron of Eu 2+ jumps back and forth between localized 4flevel and valence band. TRI Fermi-level 0.5 Ry Energy

62 Motivation Magnetic property of ε-fe. 57 Fe Mössbauer spectroscopy of ε-fe at 4.5 K and 20 GPa using DAC under external magnetic fields up to 7 T. Non-magnetic or paramagnetic with small magnetic moment.

63 Mössbauer spectra of Pd-2%Fe alloy vs. 57 Co in Rh source under various applied fields T Relative Transmission T 3 T T 7 T Velocity, v / mm s