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

Brambleby, J. and Goddard, P. A. and Singleton, J. and Jaime, M. 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. (2017) 'Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behaviour.', Physical review B., 95 (2). 024404.

Abstract

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. 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.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1103/PhysRevB.95.024404
Publisher statement:Reprinted with permission from the American Physical Society: Physical Review B 95(2): 024404 © 2017 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.
Date accepted:06 December 2016
Date deposited:25 January 2017
Date of first online publication:05 January 2017
Date first made open access:25 January 2017

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