Angle-dependent thermodynamics of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>α</mml:mi><mml:mtext>−</mml:mtext><mml:mi>Ru</mml:mi><mml:msub><mml:mi>Cl</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>
Sebastian Bachus, David A. S. Kaib, Anton Jesche, V. Tsurkan, A. Loidl, Stephen M. Winter, Alexander A. Tsirlin, Roser Valentí, P. Gegenwart
Abstract
Thermodynamics of the Kitaev honeycomb magnet $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Ru}{\mathrm{Cl}}_{3}$ is studied for different directions of in-plane magnetic field using measurements of the magnetic Gr\"uneisen parameter ${\mathrm{\ensuremath{\Gamma}}}_{B}$ and specific heat $C$. We identify two critical fields ${B}_{c}^{\mathrm{AF}1}$ and ${B}_{c}^{\mathrm{AF}2}$ corresponding, respectively, to a transition between two magnetically ordered states and the loss of magnetic order toward a quantum paramagnetic state. The ${B}_{c}^{\mathrm{AF}2}$ phase boundary reveals a narrow region of magnetic fields where inverse melting of the ordered phase may occur. No additional transitions are detected above ${B}_{c}^{\mathrm{AF}2}$ for any direction of the in-plane field, although a shoulder anomaly in ${\mathrm{\ensuremath{\Gamma}}}_{B}$ is observed systematically at $8--10\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ . Large field-induced entropy effects imply additional low-energy excitations at low fields and/or strongly field-dependent phonon entropies. Our results establish universal features of $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Ru}{\mathrm{Cl}}_{3}$ in high magnetic fields and challenge the presence of a field-induced Kitaev spin liquid in this material.