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

Zajarniuk, T.; Szewczyk, A.; Gutowska, M. U.; Puzniak, R.; Szymczak, H.; et al. // Physical Review B//

DOI: https://dx.doi.org/10.1103/PhysRevB.105.094418

Specific heat CB 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 Tc=0.68 K. Nuclear, nonphonon (Cm), and lattice contributions to CB were separated. Lowering of Tc with an increase in magnetic field parallel to the easy magnetization axis (B) was found. It was established that Cm and a Grüneisen ratio depend on B 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). The BT phase diagram was constructed, and the dynamical critical exponent 0.82z0.96 was assessed. Nature of the transition was not established explicitly. Magnetization studies point at the ferromagnetic ordering of Tb3+ magnetic moments, however, lowering of Tc with increase in B is opposite to the classical behavior. Hence, a dominant role of QFs was supposed.