Strongly anisotropic magnetocaloric effect observed in a dipolar magnet LiGdF4
The work was performed by the Department of Quantum Electronics and Radio Spectroscopy.
Lithium gadolinium tetrafluoride, which is a transparent plate 4 by 4 mm in size and 0.1 mm in thickness, was grown by Senior Research Associate of the Laboratory of Magnetic Radio Spectroscopy and Quantum Electronics Stella Korableva and Junior Research Associate of the Laboratory of Multifunctional Nanostructures and Photonics Crystals for Solutions of Fundamental Problems in Biomedicine and Materials Science Oleg Morozov.
According to Irina Romanova, Deputy Director for Research of the Institute of Physics, lithium gadolinium tetrafluorides are promising materials for quantum electronics. Scientists are particularly interested in the magnetic properties of LiGdF4, including low-temperature phase transitions.
Together with colleagues from the Institute of Physical Problems of the Russian Academy of Sciences, Sergey Sosin and Vasily Glazkov, physicists from Kazan University discovered an anisotropic magnetocaloric effect within the framework of a joint project supported by a grant from the Russian Science Foundation.
As Romanova explained, this effect is used for cooling by adiabatic demagnetization, making it possible to reach very low and ultra-low temperatures close to absolute zero.
Anisotropy is the difference in the investigated characteristics with respect to the crystallographic axes of a single crystal. If the magnetocaloric effect were the same in all directions, the cooling would be much less efficient.
“From a crystal grown by the Bridgman-Stockbarger method, we cut a plate along its plane. Measurements made in the temperature range 2-10 K showed a significant difference in cooling efficiency when an external magnetic field was applied along the a-axis and along the c-axis. The anisotropy arises from the competition of contributions to the paramagnetic susceptibility from different interactions. We have demonstrated that the magnetization of LiGdF4 crystal along the tetragonal c-axis in the specified temperature range resembles the behavior of non-interacting magnetic moments, which enhances the magnetocaloric effect to the maximum possible level of an ideal paramagnetic. The results obtained can be described in the framework of molecular field theory taking into account the Curie-Weiss temperature anisotropy. Comparison with materials used for adiabatic demagnetization shows a significant advantage of single crystal LiGdF4 in the helium temperature range (1-4 K) in moderate magnetic fields, which opens up prospects for practical applications”, explains Ruslan Batulin, Lead Research Associate of the Laboratory of Quantum Simulators.
The findings show that LiGdF4 crystal is one of the best materials for adiabatic demagnetization in the range of 1-10 Kelvin.
“Its use is potentially feasible in cascaded adiabatic demagnetization plants. The high-temperature stage operates at room temperature, while the low-temperature stage operates at ultra-low temperatures,” Romanova elaborated.
LiGdF4 monocrystal can find applications in the creation of quantum computers, lasers, and infrared telescopes.