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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

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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

Physics Department

University of California, San Diego

Bruce M. Clemens

Department of Applied Physics

Stanford University

University of California at Berkeley – Physics Department

March APS Meeting, Dallas, TX – March 24, 2011

why calorimetry
Why calorimetry?
  • What can we study with heat capacity?
    • Lattice contribution
    • Electronic contribution
    • Phase transitions
    • Magnons, Two-state system, etc.

University of California at Berkeley – Physics Department

March APS Meeting, Dallas, TX – March 24, 2011

calorimeter on a chip
“Calorimeter on a Chip”

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!

  • Specific heat of thin films
    • 30nm-200nm
    • 2K - 500K
    • 0T - 8T

What about a crystalline sample area?

2006 APS KeithleyInstrumentation Award

University of California at Berkeley – Physics Department

March APS Meeting, Dallas, TX – March 24, 2011

ion beam assisted deposition
Ion-Beam-Assisted Deposition

IBAD MgO(001)

  • 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

J.M.E. Harper, et al., J. Appl. Phys.82, 4319 (1997)

Target

Ion Source

45º

Substrate

Ion Source

Substrate

MgO Target

Figure adapted from L.S. Yu, et. Al., J. Vac. Sci. A4, 443 (1986)

University of California at Berkeley – Physics Department

March APS Meeting, Dallas, TX – March 24, 2011

synchrotron xrd of ibad mgo
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
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%

Specific heat of IBAD MgO layer. RSI 82, 023908 (2011)

University of California at Berkeley – Physics Department

March APS Meeting, Dallas, TX – March 24, 2011

growth of ferh on ibad mgo
Growth of FeRh on IBAD MgO

Mg

  • FeRh undergoes AF>FM transition just above RT
  • CsCl structure
  • Lattice constant = aMgO/√2 means

well-matched to MgO (rotated by 45º)

Rh

Fe

O

University of California at Berkeley – Physics Department

March APS Meeting, Dallas, TX – March 24, 2011

specific heat of ferh
Specific Heat of FeRh

(AFM)(1973*)

Studied two Fe-Rh alloys with different magnetic properties

Low T data explores contributions from electrons and lattice

Difference at ~120K?

* = M.J. Richardson, D. Melville, and J.A. Ricodeau. Phys. Lett. A46 153-154 (1973)

University of California at Berkeley – Physics Department

March APS Meeting, Dallas, TX – March 24, 2011

specific heat measurements
Specific Heat Measurements
  • 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

Entropic Contributions:

ΔSlatt = -5.3+/-1.5 J/mol/K

ΔSel = 1.3+/-0.2 J/mol/K

ΔSmag= 6.6+/-3.6 J/mol/K

University of California at Berkeley – Physics Department

March APS Meeting, Dallas, TX – March 24, 2011

specific heat of fe cr mmls
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
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