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

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 are consistent with a two-dimensional nature of spin excitations in the system.

arXiv comment13 pages, 14 figures

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• Enhanced spin correlations in the Bose-Einstein condensate compound Sr3Cr2O8
• Element-specific field-induced spin reorientation and an unusual tetracritical point in MnCr2S4
• Thermal fading of the $1/k^4$-tail of the momentum distribution induced by the hole anomaly
• Temperature Dependence of the Effective Interdimeric Exchange Interaction in a Weakly Coupled Antiferromagnetic Dimeric Copper Compound
• Asymmetric phase diagram and dimensional crossover in a system of spin-1/2 dimers under applied hydrostatic pressure
• Characteristic temperatures of a triplon system of dimerized quantum magnets
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• Hole-induced anomaly in the thermodynamic behavior of a one-dimensional Bose gas