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Title: Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior

We present the magnetic and thermal properties of the bosonic-superfluid phase in a spin-dimer network using both quasistatic and rapidly changing pulsed magnetic fields. The entropy derived from a heat-capacity study reveals that the pulsed-field measurements are strongly adiabatic in nature and are responsible for the onset of a significant magnetocaloric effect (MCE). In contrast to previous predictions we show that the MCE is not just confined to the critical regions, but occurs for all fields greater than zero at sufficiently low temperatures. We explain the MCE using a model of the thermal occupation of exchange-coupled dimer spin states and highlight that failure to take this effect into account inevitably leads to incorrect interpretations of experimental results. In addition, the heat capacity in our material is suggestive of an extraordinary contribution from zero-point fluctuations and appears to indicate universal behavior with different critical exponents at the two field-induced critical points. Finally, the data at the upper critical point, combined with the layered structure of the system, are consistent with a two-dimensional nature of spin excitations in the system.
Authors:
 [1] ;  [1] ; ORCiD logo [2] ; ORCiD logo [2] ;  [3] ;  [4] ;  [4] ;  [5] ;  [6] ;  [6] ;  [6] ;  [6]
  1. Univ. of Warwick, Coventry (United Kingdom)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Durham Univ., Durham (United Kingdom)
  4. Helmhotz-Zentrum Dresden Rossendorf, Dresden (Germany)
  5. Univ. of Oxford, Oxford (United Kingdom)
  6. Eastern Washington Univ., Cheney, WA (United States)
Publication Date:
Report Number(s):
LA-UR-16-28416; LA-UR-16-25496
Journal ID: ISSN 2469-9950; PRBMDO; TRN: US1701034
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 95; Journal Issue: 2; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; High Magnetic Field Science
OSTI Identifier:
1343718
Alternate Identifier(s):
OSTI ID: 1338634; OSTI ID: 1345163

Brambleby, J., Goddard, P. A., Singleton, John, Jaime, Marcelo, Lancaster, T., Huang, L., Wosnitza, J., Topping, C. V., Carreiro, K. E., Tran, H. E., Manson, Z. E., and Manson, J. L.. Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior. United States: N. p., Web. doi:10.1103/PhysRevB.95.024404.
Brambleby, J., Goddard, P. A., Singleton, John, Jaime, Marcelo, Lancaster, T., Huang, L., Wosnitza, J., Topping, C. V., Carreiro, K. E., Tran, H. E., Manson, Z. E., & Manson, J. L.. Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior. United States. doi:10.1103/PhysRevB.95.024404.
Brambleby, J., Goddard, P. A., Singleton, John, Jaime, Marcelo, Lancaster, T., Huang, L., Wosnitza, J., Topping, C. V., Carreiro, K. E., Tran, H. E., Manson, Z. E., and Manson, J. L.. 2017. "Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior". United States. doi:10.1103/PhysRevB.95.024404. https://www.osti.gov/servlets/purl/1343718.
@article{osti_1343718,
title = {Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior},
author = {Brambleby, J. and Goddard, P. A. and Singleton, John and Jaime, Marcelo and Lancaster, T. and Huang, L. and Wosnitza, J. and Topping, C. V. and Carreiro, K. E. and Tran, H. E. and Manson, Z. E. and Manson, J. L.},
abstractNote = {We present the magnetic and thermal properties of the bosonic-superfluid phase in a spin-dimer network using both quasistatic and rapidly changing pulsed magnetic fields. The entropy derived from a heat-capacity study reveals that the pulsed-field measurements are strongly adiabatic in nature and are responsible for the onset of a significant magnetocaloric effect (MCE). In contrast to previous predictions we show that the MCE is not just confined to the critical regions, but occurs for all fields greater than zero at sufficiently low temperatures. We explain the MCE using a model of the thermal occupation of exchange-coupled dimer spin states and highlight that failure to take this effect into account inevitably leads to incorrect interpretations of experimental results. In addition, the heat capacity in our material is suggestive of an extraordinary contribution from zero-point fluctuations and appears to indicate universal behavior with different critical exponents at the two field-induced critical points. Finally, the data at the upper critical point, combined with the layered structure of the system, are consistent with a two-dimensional nature of spin excitations in the system.},
doi = {10.1103/PhysRevB.95.024404},
journal = {Physical Review B},
number = 2,
volume = 95,
place = {United States},
year = {2017},
month = {1}
}

Works referenced in this record:

Ordering, metastability and phase transitions in two-dimensional systems
journal, April 1973
  • Kosterlitz, J M; Thouless, D J
  • Journal of Physics C: Solid State Physics, Vol. 6, Issue 7, p. 1181-1203
  • DOI: 10.1088/0022-3719/6/7/010