Low-temperature thermodynamics of metamagnetism in insulating DyVO4

Even though abundant research has focused on metamagnetic critical end points in itinerant magnets, this critical phenomenon for magnetic insulators is still to be explored extensively. ${\mathrm{DyVO}}_{4}$, a magnetic insulator exhibits a field induced first order metamagnetic transition (MMT), which has previously been investigated via thermodynamic measurements. In this work, we extend our investigations down to mK temperatures and probe the metamagnetic tricritical point (TCP) directly via the magnetocaloric effect (MCE). Heat capacity reveals an inimitable phase diagram where the second order antiferromagnetic phase transition terminates at the TCP, beyond which it continues as a line of first order MMT as the temperature is lowered towards 0 K. The sample temperature and magnetic Gr\"uneisen parameter $({\mathrm{\ensuremath{\Gamma}}}_{m})$ evaluated from MCE data show direct evidence of critical fluctuations and enhanced entropy in the vicinity of the TCP. These fluctuations are also supported by diverging susceptibility observed near the TCP. Critical analysis of magnetization suggests that the metamagnetic TCP in ${\mathrm{DyVO}}_{4}$ does not belong to any universal class. However, the extracted exponents agree with another insulating metamagnet, ${\mathrm{HoMnO}}_{3}$ [Phys. Rev. Lett. 110, 157202 (2013)], suggesting the presence of a unique universality class for metamagnetic critical systems.