Wydarzenia

Dnia 2023-04-18 o godzinie 13:15 w sali 2011 Wydziału Fizyki odbędzie się wykład, na którym ddr Tatiana Zajarniuk z Instytutu Fizyki PAN w Warszawie wygłosi wykład pt:

Magnetic phase transitions in Dy³⁺ and Tb³⁺ aluminoborates below 700 mK and their nature: quantum or classical.

Serdecznie zapraszamy

Andrzej Maziewski

Jerzy Przeszowski

Magnetic phase transitions in Dy³⁺ and Tb³⁺ aluminoborates below 700 mK and their nature: quantum or classical.

Tatiana Zajarniuk

Rare earth aluminum borates RAl₃(BO₃)₄ (R-rare earth ion) crystallize in the trigonal system with space group R32 [1]. They are very attractive materials in the view of their physical properties. For example, it was proven in ref. [2], that the aluminoborates exhibit a very strong magnetoelectric effect. The aluminoborates are very interesting materials also from the point of view of applications. e.g., the YAl₃(BO₃)₄ and GdAl₃(BO₃)₄ compounds doped with Nd are applied in self frequency doubling lasers and NdAl₃(BO₃)₄ is used in minilasers [3].

Specific heat, C_B, of a Tb³⁺ and Dy³⁺ aluminoborates were studied for temperatures 50 mK < T < 300 K, with emphasis on the T < 1 K range, where a phase transitions were found at temperature about 0.6 K. To analyze the obtained results, the magnetic contribution to C_B was extracted from the total specific heat measured. It was done by considering three contributions to C_B, i.e.: the lattice, nuclear, and magnetic ones. The magnetic contribution was determined by subtracting the estimated lattice and nuclear contributions from the total C_B.

Based on the specific heat and magnetization studies, the magnetic Grüneisen ratio, being the most informative parameter, diverging in the vicinity of quantum transitions, was calculated by using the following formula[4,5]:

The behaviors of both the specific heat and the Grüneisen coefficient Γ as a function of T and of B|| are characteristic of the systems, in which the classical phase transition line is influenced by quantum fluctuations, QF, and ends at a quantum critical point. Based on all the results, we suppose that QF dominate the behavior of the system and destroy the long range order, i.e., we suppose the transition found to have a quantum character.

The interpretation that we deal with the transition to the ferromagnetic order of the magnetic moments of the rare earth ion is the most natural, intuitive, and supported by the M studies. However, such a transition should be smeared and shifted to higher T by B||, while we observe the opposite effect. Thus, other mechanisms cannot be ruled out. The results of the research on terbium aluminoborate were published in the article [6].

Acknowledgements:

This work was supported partially by the National Science Centre (NCN), Poland, under Project No. 2018/31/B/ST3/03289.

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[6] T. Zajarniuk, A. Szewczyk, P. Wisniewski, M. U. Gutowska, R. Puzniak, H. Szymczak, I. Gudim, V. A. Bedarev, and M. I. Pashchenko, Phys. Rev. B 105 094418 (2022).