sept. 14 th 2004 montauk, long island, ny jason s. gardner nist, center for neutron research,...
TRANSCRIPT
![Page 1: Sept. 14 th 2004 Montauk, Long Island, NY Jason S. Gardner NIST, Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg,](https://reader033.vdocuments.us/reader033/viewer/2022051316/56649f395503460f94c55e8d/html5/thumbnails/1.jpg)
Sept. 14th 2004 Montauk, Long Island, NY
Jason S. Gardner
NIST, Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899-8562
Department of Physics,Brookhaven National Laboratory,Upton, NY 11973-5000.
Neutron Scattering Studies of
Magnetically Frustrated Pyrochlores
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Pyrochlore Lattice
?
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Diffuse Scattering
(0,0,l)
(h,h
,0)
Tb2Ti2O7
JS Gardner et al., Phys. Rev. B 64, 224416 (2001).
0
200
400
600
800
1000
1200
1400
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Net
Inte
nsi
ty (
coun
ts/2
min
)
Q ( Å -1)
Y2Mo2O7
J S Gardner et al., Phys. Rev. Lett., 83, 211 (1999).
Ho2Ti2O7
ST Bramwell et al. PRL 87, 047205 (2001).
S.-H. Lee et al. Nature 418, 856 (2002)
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Outline Spin dynamicsSpin dynamics
3 Compounds3 Compounds
Antiferromagnetic frustrated Antiferromagnetic frustrated systemssystems–YbYb22TiTi22OO77, Gd, Gd22TiTi22OO77
»Strange dynamics and partial ordering
Ferromagnetic frustrated Ferromagnetic frustrated systemssystems–HoHo22TiTi22OO77
»Spin Ice (Uniquely frozen)
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Sept. 14th 2004 Montauk, Long Island, NY
Spin Echo Principle
I(Q,t) = S(Q,)cos(t)dCosine transform
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New Spectrometer
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Typical Magnetic Neutron Spin Echo
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0.01 0.1 1
25.0K22.5K
18.9K10.0K
S(Q
,t)/S
(Q,0
)
Time (ns)
50 %
0.009
0.01
0.011
0.012
0.013
0.014
0.015
5 10 15 20 25 30 35 40
M/H
(em
u/m
ol)
Temperature (K)
22.5 KZFC
FC
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Sept. 14th 2004 Montauk, Long Island, NY
Spin Ice
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FM Spin Ices – RE2Ti2O7 (Ho and Dy)
K. Matsuhira et al., J. Phys.: Condens. Matter 12 (2000) L649–L656 and 13 (2001) L737-L746
Ho2Ti2O7
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FM Spin Ice
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Correlation
J Snyder et al. PRB 69 064414 (2004)
Mag
(ar
b. u
nits
)
Ho2Ti2O7
Dy2Ti2O7
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Spin Echo Results
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New Spectrometer
New territory
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New Data
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Sept. 14th 2004 Montauk, Long Island, NY
Partial Order
Gd2Ti2O7 -- ½ filled orbital -- Experimental realisation of a Heisenberg spin on a pyrochlore lattice-- found to order????-- very anisotropic??
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Gd2Ti2O7 - Partially ordered
A. P. Ramirez, et al.. Rev. Lett. 89, 067202 (2002)
1.1K
0.7K
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Powder diffraction
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Magnetic Structure
A B
C D
1k 4k
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NPD (Champion et al. Rev. B 64, 140407 (2001))
Kagome Planes
INTERSTITIAL SITE
∑ = 0N=1
∞
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0.77 K Transition
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50 mK StructureA B
C D
1k 4k
RED circlesBLUE balls
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0.77 K Transition
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What else do we know….A. P. Ramirez, et al.. Rev. Lett. 89, 067202 (2002)
(000)
(½½½)
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Neutron Spin Echo (preliminary results)
¾
¼
T > 1K Entire spin system is inelastic and
T < 1K 25% of the spin system is static
REM: NPD revealed 75% of the system is static below the 1st transition; At all T, NSE fits results in a S(Q,t)/S(q,0)
as t 0 of 75%.
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Sept. 14th 2004 Montauk, Long Island, NY
More Unusual Magnetism
-Yb-Yb22TiTi22OO77
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Yb2Ti2O7
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New Data
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Conclusions
Exotic Magnetic Order
Large moment systems
Big crystals
NSE ideal time () window
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Sept. 14th 2004 Montauk, Long Island, NY
Collaborators
G Ehlers (SNS)
A Cornelius (UNLV)
R Stewart (ILL)
S Bramwell, A Wills and T Fennell(UCL)
Nick Rosov (NIST)