1. LLNL-PRES-680527
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore
National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC
High-magnetic field suppression of
antiferromagnetism in USb2
Ryan L. Stillwell
Lawrence Livermore National Laboratory
Physical Phenomena at High Magnetic Fields VIII
Tallahassee, FL
January 7, 2016

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Collaborators
Jason Jeffries
Lawrence Livermore
National Laboratory
NIST Center for Neutron Research
and U. Maryland
Nicholas Butch
I-Lin Liu
Marcelo Jaime
Neil Harrison
NHMFL-Pulsed Field Facility
Los Alamos National Laboratory

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Outline
Why USb2?
Part One: Magnetostriction
—AFM suppression seen via fiber Bragg
dilatometer
Part Two: Magnetization
—AFM suppression confirmed via extraction
coil magnetometer

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 Antiferromagnet below TN=202K
— High energy scales involved
 Highly anisotropic, quasi-two
dimensional structure
 U 5f-electrons are hybridized
 Fermi surface reconstruction
going from paramagnetic to
antiferromagnetic phase
Introduction to USb2
D. Aoki et al., Phil. Mag. B, 80, 1517 (2000)
Paramagnetic
Antiferromagnetic

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D. Aoki et al., Phil. Mag. B, 80, 1517 (2000)
USb2 AFM unit cell is 2x the chemical unit cell
AFM unit cell
chemical unit cell
Paramagnetic
Antiferromagnetic

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Part One
Magnetostriction

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Fiber Bragg dilatometer avoids eddy current
heating and enables measurements in pulsed fields
c-axis//H
1 mm a-b plane//H
Had to stack 6 crystals
a) b) c)
d)
R. Daou et al., RSI, 81, 033909 (2010)
M. Jaime et al., PNAS, 31, 12404 (2012)
A. Grockowiak, in preparation

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Thermal contraction along a-b plane confirms
AFM transition at TN= 202K
TN

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USb2 does not show AFM transition in
magnetostriction along the a-b plane

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vertical offset for clarity
USb2 shows AFM transition in magnetostriction
along the c axis

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H-T phase diagram of AFM-PM transition
observed via magnetostriction along the c axis

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What is the high-field magnetic structure?
Is there a change from 2nd to 1st order at lower T?
vertical offset for clarity

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Part Two
Magnetization

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USb2 sample loading for extraction coil
magnetometry
Sample with c-axis coming out of the picture
Sample is ~50μm thick100μm
Compensated coils for
magnetization measurements
Sample outSample in

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USb2 extraction coil magnetometry clearly
shows AFM transition

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USb2 phase diagram matches well between
magnetostriction and magnetization

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 Established first H-T phase diagram of USb2.
 Magnetostriction and magnetization phase boundaries agree.
 High-field, low-temperature magnetic state still unclear
(ie. PM or canted-AFM) due to field limitation.
 Quantum oscillations to see Fermi surface above Hc?
 Experiment on UBi2 to see possible Fermi surface effects.
Conclusions and Future Work

18. Thank You!

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Quantitative analysis via corrected background
gives magnetic moment smaller by ~0.8μB

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USb2 AFM transition in magnetostriction along
the c axis downsweep

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High field magnetostriction along c-axis

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Structures of all UX2 compounds
D. Aoki et al., Phil. Mag. B, 80, 1517 (2000)