Quantum versus classical nature of the low-temperature magnetic phase transition in TbAl3(BO3)4

Specific heat C-B of a TbAl3(BO3)(4) crystal was studied for 50 mK < T < 300 K with emphasis on T < 1 K where a phase transition was found at T-c = 0.68 K. Nuclear, nonphonon (C-m), and lattice contributions to C-B were separated. Lowering of T-c with an increase in magnetic field parallel to the easy magnetization axis (B-parallel to) was found. It was established that C-m and a Gruneisen ratio depend on B-parallel to and T in a way characteristic of systems in which a classical transition is driven by quantum fluctuations (QFs) to a quantum critical point at T = 0 by tuning a control parameter (B-parallel to). The B-parallel to - T phase diagram was constructed, and the dynamical critical exponent 0.82 <= z <= 0.96 was assessed. Nature of the transition was not established explicitly. Magnetization studies point at the ferromagnetic ordering of Tb3+ magnetic moments, however, lowering of T-c with increase in B-parallel to is opposite to the classical behavior. Hence, a dominant role of QFs was supposed.

Automated summary

The specific heat of a TbAl3(BO3)(4) crystal was studied, and a phase transition was found at low temperatures. The results showed that an increase in magnetic field can lower the transition temperature, and the specific heat and Gruneisen ratio exhibited characteristics of a quantum critical point. By constructing a phase diagram and assessing the critical exponent, the nature of the system was revealed. Magnetization studies indicated ferromagnetic ordering, but contrary to classical behavior, suggesting a dominant role of quantum fluctuations in the phase transition.