1. TNéel
TMIT
Abhijit Biswas, et al. 4
The unintended height of a
crystal placed in a powder x-
ray diffractometer shifts
the Bragg peak locations3:
2 c sin Θ −
H
R
cos Θ = L λ
x = 0
x = 0.34
…where H is the height offset and R is the diffractometer radius.
Two samples’
peaks differing at
the (00L)-type
peak 0010
Motivation
Magnetic and ElectronicTransitions in a Highly-Doped Mott Insulator
Michael Aling, Dr. Julian Schmehr, Prof. Stephen D.Wilson
UCSB Department of Materials
It is hoped that this study will reveal new
phases in an electronically-useful material.
Cousins of this Ruddlesden-Popper ruthenium-
doped strontium iridate become superconducting at
low temperatures, while also exhibiting other rich
physical phenomena: fermi liquid ground states,
metamagnetism, colossal magnetoresistance, and
multiple electronic transitions. Sr3Ir2O7’s relation to
cuprate high-temperature superconductors is
further motivation for study.1
The Parent Compounds Previous Work1
Continuing and FutureWork
Doping Sr3(Ir1-xRux)2O7
References
Identifying Electronic & Magnetic Phases
Unusual percolative phase transitions in
Sr3(Ir1-xRux)2O7 impact properties:
300
1000
0
Temperature(K)
Ru level (%)
*
Interaction strengthens AF order
when it would otherwise die off (*)
Crosssectionschematic
(asinglecrystal)
Adapting x-ray diffraction to save time and preserve samples
Paramagnetism
(PM)
Antiferromagnetism
(AF)
Resistivity Analysis RevealsTransitions
Studying little-known region: 40% to 60% Ru
(Will add error bars)
(Should also add powder points)
Sr3Ir2O7 (“327”), a Mott insulator, has a smaller
bandgap than its “214” cousin, making it an ideal
candidate to be doped in order to probe the
combination of crystal field splitting, spin-orbit
coupling, and small Coulomb interaction which
together make it insulating.1, 2 Sr3Ru2O7 is a metal
with paramagnetic disorder (contrasting the iridate’s
low-temperature antiferromagnetism) near a
magnetic instability.1
No transitions observed
at x=0.62
Progress on Phase
Diagram
When this material
becomes metallic,
it is only because a
network of
metallic pockets
begins to join
(percolative
threshold.) In
both the insulating
and metallic
regimes, regions of
both phases
coexist on a
nanometer scale.
Utilizing Lattice Parameter Contraction
Dopant Distribution in Growths
(Each point represents one crystal)
About 5 samples
found in desired
range, across 3
growths
Dopant level varies greatly in flux
growths. X-ray diffraction (XRD)
is faster and less costly than
EDX (energy-dispersive x-ray
spectroscopy).While EDX
directly analyzes concentrations,
this technique offers an indirect
method.
Nonlinearity caused by
pull of competing
nanometer-scale
regions
A MATLAB program translates
information about peak location into
the lattice parameter c by solving
the system numerically.
The results from this single-crystal
method are as accurate as powder
results from the previous study.
Lattice Parameter by Dopant Level
(Each point represents one sample)
Temperature(K)
Metal-insulator
Magnetic
Lattice Parameter Solver
The MATLAB program will be
expanded into a full Rietveld
refinement capable of overcoming
the primary challenge associated
with a single-crystal technique:
resolving peak splitting due to
uneven crystal surfaces. Human
error will also be reduced by the
further automation of the process.
After first completing the survey of
the x=0.4 to 0.6 region by gathering
heat capacity, magnetization, and
sub-Kelvin resistivity (temperatures
at which cousin compounds become
superconducting), further growths
focused around x=0.75 will push
forward into a regime even less-
studied.
People
Michael Aling
Sophomore
Mechanical Engineering
Julian Schmehr
Postdoctoral Scholar
Materials Science
Stephen D. Wilson
Principal Investigator
Materials Science
1. Dhital, C. et al. Carrier localization and electronic phase separation in a
doped spin-orbit-driven Mott phase in Sr3(Ir1-xRux)2O7. Nat. Commun.
(2014).
2. Dhital, C. et al. Spin ordering and electronic texture in the bilayer iridate
Sr3(Ir1-xRux)2O7. Physical Review B 86, 100401(R) (2012).
3. Jesche,A. et al. X-Ray diffraction on large single crystals using a powder
diffractometer. Philosophical Magazine (2016).
4. Abhijit Biswas, Ki-Seok Kim andYoon Hee Jeong (2016). Metal–Insulator
Transitions and Non-Fermi Liquid Behaviors in 5d Perovskite Iridates,
Perovskite Materials - Synthesis, Characterisation, Properties, and
Applications, Dr. Likun Pan (Ed.), InTech, DOI: 10.5772/61285.
Both adapted from 1
Supported by NSF CAREER-Award DMR-1056625