Download presentation

Presentation is loading. Please wait.

Published byHayley Raybourn Modified over 2 years ago

1
Spin dynamics of stripe-ordered layered nickelates Andrew Boothroyd Department of Physics, Oxford University Ni 2+ (S=1) Ni 3+ (S=1/2) Cu 2+ (S=1/2) Cu ~2.5+ La 2–x Sr x NiO 4 (La,Nd) 2–x (Sr,Ba) x CuO 4 (x~1/8) ● Spin waves in La 5/3 Sr 1/3 NiO 4 ● Magnetic ‘resonance’ ● quasi 1D spin correlations ● Inward dispersion in La 2 NiO 4.11 ● Low energy charge dynamics

2
Acknowledgements Paul Freeman Institut Laue-Langevin / Oxford University D. Prabhakaran Oxford University(Single crystals) Stephen HaydenUniversity of Bristol Hyungje Woo Brookhaven National Lab / ISIS / Oak Ridge John Tranquada Brookhaven National Lab Marcus Huecker Kenji NakajimaUniversity of Tokyo Michael JohnstonUniversity of Oxford James Lloyd-Hughes Mechthild Enderle Institut Laue-Langevin Jiri Kulda Arno Hiess Felix AltorferPaul-Scherrer Institut,Switzerland Christof Niedermayer Chris FrostISIS Facility Toby Perring

3
Stripe order in La 2–x Sr x NiO 4 x = 0 x = 1/4x = 1/3x = 1/2 (Tranquada et al, Cheong et al, Yoshizawa et al) ideal stripe structures Ni 2+ (S = 1) Ni 3+ (S = ½)

4
Stripe order in La 5/3 Sr 1/3 NiO 4

5
Constant-energy slices projected onto the a*b* plane. Data from MAPS spectrometer. Neutron scattering from La 5/3 Sr 1/3 NiO 4

6
Woo et al. PRB 72, 064437 (2005) 1. Spin wave model for La 5/3 Sr 1/3 NiO 4

7
Spin wave dispersion in La 5/3 Sr 1/3 NiO 4 0 0.5 1 1 Q x (r.l.u.) Q y (r.l.u.) Linear spin wave model provides good description of Spin excitation spectrum for energies > ~30 meV

8
2. Mystery ‘resonance’ in spin excitation spectrum of La 5/3 Sr 1/3 NiO 4 unpolarized neutrons (MAPS time-of-flight, RAL) polarized neutrons (IN20 triple-axis, ILL) Boothroyd et al, PRB 67, 100407(R) (2003) Out-of-plane anisotropy gap Broadening above 6 meV 0 0.5 1 1 Q x (r.l.u.) Q y (r.l.u.)

9
Spin wave dispersion in La 5/3 Sr 1/3 NiO 4 0 0.5 1 1 Q x (r.l.u.) Q y (r.l.u.)

10
E = 2.5 meV 3. Low energy spin fluctuations in La 5/3 Sr 1/3 NiO 4 Boothroyd et al, PRL 91, 257201 (2003) E = 5 meV E = 0 meV (elastic)

11
Diffuse inelastic scattering Consistent with quasi-1D AFM chains Low energy quasi-1D spin fluctuation in La 5/3 Sr 1/3 NiO 4 Scans along line B Scan along line A B

12
4. Inward dispersion of spin waves in La 2 NiO 4.11 Christensen et al. PRL 93, 147002 (2004) Vignolle et al. Nature Phys. 3, 163 (2007) Spin excitation spectrum of La 1.84 Sr 0.16 CuO 4 0 0.5 1 1 Q x (r.l.u.) Q y (r.l.u.)

13
Inward dispersion of spin waves in La 2 NiO 4.11 0 0.5 1 1 Q x (r.l.u.) Q y (r.l.u.) Freeman et al., JMMM 310, 760 (2007)

14
Inward dispersion of spin waves in La 2 NiO 4.11 Yao and Carlson, PRB 73, 224525 (2006) Linear spin wave theory J 1 = 0.1J J 1 = 0.5J

15
Lloyd-Hughes, PRB 77, 195114 (2008) Optical conductivity, THz spectroscopy x = 0.333 x = 0.275 5. Low energy charge dynamics in La 2–x Sr x NiO 4

16
Lloyd-Hughes, PRB 77, 195114 (2008) x = 0.333 x = 0.275 Low energy charge dynamics in La 2–x Sr x NiO 4 Thermally activated charge response with energy ~5meV

17
Summary — spin and charge excitations in La 2–x Sr x NiO 4 Summary — spin and charge excitations in La 2–x Sr x NiO 4 1. E > 30 meV: spin-wave-like modes on a rigid stripe superlattice; spin wave model for La 5/3 Sr 1/3 NiO 4 intra- and inter-stripe exchange 2. Mysterious magnetic ‘resonance’ peak at ~25 meV 3. AFM spin fluctuations along charge stripes 4. Inward magnetic dispersion observed at x ~ ¼ 5. Low energy charge mode at ~5 meV

18
Hybridization with another excitation?

19
Possible magnetic ground state for La 5/3 Sr 1/3 NiO 4 ? Klingeler et al; M. Long (unpublished) 0 0.5 1 1 Q x (r.l.u.) Q y (r.l.u.) Non-collinear magnetic structure

20
Spin reorientation transition La 3/2 Sr 1/2 NiO 4 La 1.67 Sr 0.33 NiO 4 ● On cooling, spins rotate away from stripe direction ● Reorientation observed for 0.275 < x < 0.5 ● Most prominent for x = 1/3 ( Df = 13 deg) and x = 1/2 ( Df = 26 deg) Freeman et al, PRB 66, 212405 (2002), Freeman et al, PRB 70, 024413 (2004) Lee et al, Phys. Rev. B 63, 60405(R) (2001),

21
Spin wave model for La 5/3 Sr 1/3 NiO 4 J = 15 ± 1.5 meV J’ = 7.5 ± 1.5 meV K c = 0.07 ± 0.01 meV Boothroyd et al. PRB 67, 100407 (2003)

22
Temperature dependence of 25meV mode Freeman et al, JPCM 20, 104229 (2008) Polarised neutron scattering

23
Determination of out-of-plane anisotropy gap 1.Compare spectra obtained with in-plane and out-of-plane scattering vectors 2.Separate different directional components of spin fluctuations by neutron polarization analysis S c = spin fluctuations along c axis S || = … … parallel to stripes x = 0.33

24
Spin excitations as function of x in La 2–x Sr x NiO 4 E = 40 meV Broadening when x 1/3 dispersion

25
Energy gap D = 1.45 ± 0.07 meV G = 1.54 ± 0.14 meV Fit to Lorentzian with gap D

26
Scans along line B Temperature dependence Diffuse inelastic scattering

27
Low energy mode follows zone boundary

28
Polarization of low energy mode Neutron polarization analysis of low energy mode: Intensity of spin fluctuations along c axis is factor 2.3 ± 0.4 larger than in plane

Similar presentations

OK

Collin Broholm Johns Hopkins University and NIST Center for Neutron Research Quantum Phase Transition in a Quasi-two-dimensional Frustrated Magnet M. A.

Collin Broholm Johns Hopkins University and NIST Center for Neutron Research Quantum Phase Transition in a Quasi-two-dimensional Frustrated Magnet M. A.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on liquid crystal display Ppt on job evaluation definition Ppt on safe drinking water Ppt on business marketing management Ppt on oxygen cycle for class 9 Download ppt on life cycle of butterfly Ppt online open house Ppt on bmc remedy software Ppt on campus recruiting systems Download ppt on mind controlled robotic arms