University of California at Berkeley – Physics Department
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University of California at Berkeley – Physics Department ch APS Meeting, Dallas, TX – March 24, 2011 Calorimetry of epitaxial thin films David W. Cooke, Frances Hellman Physics Department, University of California, Berkeley Stephanie Moyerman Eric E. Fullerton Physics Department University of California, San Diego Bruce M. Clemens Department of Applied Physics Stanford University J. Randy Groves Superconductivity Technology Center Los Alamos National Laboratory Rev. Sci. Instr. 82, 023908 (2011)
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Calorimetry of epitaxial thin films. Rev. Sci. Instr. 82 , 023908 (2011). David W. Cooke, Frances Hellman Physics Department, University of California, Berkeley. J. Randy Groves Superconductivity Technology Center Los Alamos National Laboratory. Stephanie Moyerman Eric E. Fullerton - PowerPoint PPT Presentation
Transcript of University of California at Berkeley – Physics Department
University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
Calorimetry of epitaxial thin films
David W. Cooke, Frances HellmanPhysics Department, University of California, Berkeley
Stephanie MoyermanEric E. Fullerton
Physics DepartmentUniversity of California, San Diego
Bruce M. ClemensDepartment of Applied Physics
Stanford University
J. Randy GrovesSuperconductivity Technology
CenterLos Alamos National Laboratory
Rev. Sci. Instr. 82, 023908 (2011)
Why calorimetry?
• What can we study with heat capacity?– Lattice contribution
– Electronic contribution
– Phase transitions– Magnons, Two-state system, etc.
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University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
“Calorimeter on a Chip”
• Specific heat of thin films– 30nm-200nm– 2K - 500K– 0T - 8T
2006 APS KeithleyInstrumentation Award
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University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
Limitation?
Many thin films are of interest because can use epitaxy/strain to alter bulk-like properties, but need membrane to reduce heat link while having small addenda!
What about a crystalline sample area?
Ion-Beam-Assisted Deposition
IBAD MgO(001)
J.M.E. Harper, et al., J. Appl. Phys. 82, 4319 (1997)
45º
MgO Target
Substrate
TargetIon Source
SubstrateIon Source
Figure adapted from L.S. Yu, et. Al., J. Vac. Sci. A 4, 443 (1986)
• MgO grows (001)-textured out-of-plane
• 45º to substrate yields (110) in-plane due to channeling
• Provides biaxially-oriented substrate
• Can be grown on any substrate
• Used by the superconductivity community for years
University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
Synchrotron XRD of IBAD MgO
• Peaks displaced from MgO (hkl) values
• Distortion along beam axis ([202]):• a = .4228nm [020]• b = .4202nm [200]• c = .4212nm [002] (same as bulk)
hk reciprocal space map. RSI 82, 023908 (2011)
University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
Heat Capacity of IBAD MgO
• ~25nm IBAD MgO grown on 200nm SiNx membrane
• Matches MgO CP well at high T
• Softening of lattice observed
Total addition to background < 6.5%
University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
Specific heat of IBAD MgO layer. RSI 82, 023908 (2011)
Growth of FeRh on IBAD MgO
• FeRh undergoes AF>FM transition just above RT• CsCl structure
• Lattice constant = aMgO/√2 means
well-matched to MgO (rotated by 45º)
University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
Mg
ORh
Fe
University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
Specific Heat of FeRh
(AFM)(1973*)
* = M.J. Richardson, D. Melville, and J.A. Ricodeau. Phys. Lett. A 46 153-154 (1973)
Studied two Fe-Rh alloys with different magnetic properties
Low T data explores contributions from electrons and lattice
Difference at ~120K?
Entropic Contributions:ΔSlatt = -5.3+/-1.5 J/mol/KΔSel = 1.3+/-0.2 J/mol/KΔSmag= 6.6+/-3.6 J/mol/K
• Clatt is approximated with Debye models combining low T data and sound velocity measurements
• Cel is obtained from γT, as measured in low T CP
University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
Specific Heat Measurements
Specific heat of Fe/Cr MMLs• Measured Fe/Cr MMLs on IBAD MgO to study interfacial enhancement of N(εF)
• XRD: Well-preserved superlattice order and four-fold symmetry indicating epitaxy
• Film on IBAD MgO shows lowest enhancement, indicating role of disorder
University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
Conclusions
• Photoemission: Observed change in electronic density of states between AF/FM phases
• Specific Heat: Observed Schottky-like anomaly suggesting dominant contribution of magnetism to entropy of transition
University of California at Berkeley – Physics Department
March APS Meeting, Dallas, TX – March 24, 2011
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