Transcript S P I N

NIST Summer School on Neutron Spectroscopy
Seung-Hun Lee
Peter Gehring
Sungil Park
Spin Polarized Inelastic Neutron Scattering
Alina Visinoiu
Gokhan Caliskan
Erick Lawson
Martin Sulic
Tessema Guebre Xabiher
Kapil Gupta
Jose Rodriguez
Mike Lewis
ZnCr2O4-Space Group-Fm3d
Edge-sharing octahedra
Magnetic frustration
H = -J S Si . Sj
O
AFM
A
B
Corner-sharing tetrahedra (B sites)
or
All exchange
interactions can
not be satisfied.
Magnetic Phase Transition in ZnCr2O4
QCW = -390
K
TN = 12.5 K
SPINS
Neutron Source
Sample
Single Detector
Analyzer
Monochromator
Sample
Position-Sensitive
Detector
Increased data acquisition
Rate over conventional TAS
By an order of magnitude.
D2qi
Flat Analyzer qai q
a
Exploring Statics
(H,K,L)=(1,1,1)
(1/2,1/2,1)
Intensity
•Q resolution~0.02 Å-1
•Doubling of the unit cell
(1/2,1/2,3/2)
Q(Å-1)
Order Parameter
Exploring Dynamics
Energy scans at fixed Q at 2K and 15K
4.00
3.50
Inelastic
2K
3.00
15K
Quasielastic
I [cts]
2.50
2.00
1.50
1.00
0.50
0.00
-1
0
1
2
3
Energy [meV]
4
5
6
7
Inelastic Resonance Peak
-Correlation Length
T=15K>TN
0.6meV<E<1.4meV
HWHM=~0.45Å
~2.2Å
T=1.5K<TN
4.2meV<E<1.4meV
HWHM=~0.36Å
~2.8Å
Summary
• SPINS probes both the static crystal and
magnetic state of the system.
• SPINS probes the dynamic behavior of the
system.
• SPINS is a relatively fast spectroscopy
technique.
• SPINS is ideal for studying specific regions
in Q- space.
Acknowledgements:
•NIST
•NSF
•NCNR