Strong conventional and rotating magnetocaloric effects in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>TbV</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> crystals over a wide cryogenic temperature range
M. Ballı, S. Mansouri, Dimitre Dimitrov, P. Fournier, S. Jandl, Jenh‐Yih Juang
Abstract
It is known that the zircon-type orthovanadates $\mathrm{RV}{\mathrm{O}}_{4}$ show promise in many different applications as catalysts and optical materials. In this work, we demonstrate that the $\mathrm{TbV}{\mathrm{O}}_{4}$ compound can be also used as magnetic refrigerant in efficient and ecofriendly cryocoolers due to its strong magnetocaloric effect at low-temperature regime. The application of a relatively low magnetic field of 2 T along the easy magnetization axis ($a$) gives rise to a maximum entropy change of about 20 J/kg K at 4 K. More interestingly, under sufficiently high magnetic fields, the isothermal entropy change $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{\mathrm{T}}$ remains approximately constant over a wide temperature range which is highly appreciated from a practical point of view. In the magnetic field change of 7 T, $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{\mathrm{T}}$ that reaches roughly 22 J/kg K remains practically unchanged between 0 and 34 K leading to an outstanding refrigerant capacity of about 823 J/kg. On the other hand, the lowering of crystallographic symmetry from the tetragonal to the orthorhombic structure occurring close to 33 K as confirmed by Raman scattering data results in a strong magnetic anisotropy. Accordingly, strong thermal effects can be also obtained simply by spinning the $\mathrm{TbV}{\mathrm{O}}_{4}$ single crystals between their hard and easy orientations in constant magnetic fields instead of the standard magnetization-demagnetization process. Such rotating magnetocaloric effects would open the way for the implementation of $\mathrm{TbV}{\mathrm{O}}_{4}$ in a new generation of compact and simplified magnetic refrigerators that can be dedicated to the liquefaction of hydrogen and helium.