Giant rotating magnetocaloric effect at low magnetic fields in multiferroic TbMn2O5 single crystals

Abstract

Solid state-refrigerants have generated worldwide interest owing to their growing potential for use in efficient and green cooling devices. Caloric effects could be obtained by manipulating their degrees of freedom such as magnetization, electric polarization and volume using a variable external field. In conventional magnetocaloric refrigeration systems, the magnetocaloric effect is exploited by moving the active material in and out of the magnetic field source. Here we demonstrate that a giant and reversible magnetocaloric effect can be generated simply by rotating the multiferroic TbMn 2 O 5 single crystal around its b axis in a relatively low constant magnetic field applied in the ac plane. For a magnetic field applied along the easy axis a, we report an entropy change of 12.25 J/kg K at about 10 K in a field change of 5 T which is 100 times larger than that found when the field is applied along the hard axis c. When the TbMn 2 O 5 is rotated with the field remaining in the ac plane, the associated adiabatic temperature change reaches minimum values of 8 K and 14 K under 2 T and 5 T, respectively. This giant rotating magnetocaloric effect in TbMn 2 O 5 is caused by the "colossal" anisotropy of the entropy change, the enhancement of the magnetization under relatively moderate magnetic fields and the lower magnitude of specific heat. On the other hand, the application of the coherent rotational model demonstrates that the rotating magnetocaloric effect exhibited by TbMn 2 O 5 does not originate directly from the magnetocrystalline anisotropy. Our results should inspire and open new ways toward the implementation of compact, efficient and embedded magnetocaloric devices for low temperature and space application. Its potential operating temperature range of 2 to 30K makes it a great candidate for the liquefaction of hydrogen.

Analysis of the Anisotropic Magnetocaloric Effect in RMn2O5 Single Crystals

“…Consequently, a large MCE could be obtained by rotating them between their easy and hard-axes in constant magnetic fields (Figure 1), instead of the conventional magnetization-demagnetization process (via field variation) [15,16,30,31]. This would enable the implementation of more compact and efficient magnetic refrigeration devices with a simplified design [1,15,16]. However, as presented below, the RMCE shown by the RMn2O5 oxides markedly depends on the rare earth element.…”

“…The analysis of different Raman excitations confirms that the high-quality crystals under study form in an orthorhombic symmetry with the Pbam space group. It It is worth noting that the magnetocaloric properties and particularly the RMCE were separately reported in RMn 2 O 5 (R = Ho, Tb) multiferroics [15,16]. However, in order to provide the reader with the big picture of the RMCE shown by these materials, we consider that it is important to firstly discuss and compare their magnetic and magnetocaloric properties in Section 2.…”

“…In this context, the RMn 2 O 5 (R = magnetic rare-earth element) multiferroics seem to be alternative candidates for magnetocaloric tasks around 10 K [15,16,[25][26][27][28][29]. These compounds unveil complex crystalline and magnetic structures which results in a wide range of fascinating electrical and magnetic…”

“…However, the search for materials with excellent magnetocaloric properties in the temperature range from about 2 to 30 K is of great interest from fundamental, practical, and economical points of view, due to their potential use as refrigerants in several low temperature applications such as the space industry, scientific instruments, and gas liquefaction [14][15][16][17][18][19][20][21][22][23][24][25]. On the other hand, the development of new designs that can render magnetic cooling more competitive is also a key parameter for the commercialization of this emergent technology.…”

Review of the Magnetocaloric Effect in RMnO3 and RMn2O5 Multiferroic Crystals

“…In addition, as claimed by Barclay et al [18], a large scale utilization of hydrogen as a source of energy will result in better energy security with major environmental, economic, and social benefits. In this context, several cryomagnetocaloric materials have been proposed [19][20][21][22][23][24][25][26][27][28]. Following this, Matsumoto et al [29,30] unveiled a reciprocating magnetic refrigerator dedicated to hydrogen liquefaction that uses the Dy 2.4 Gd 0.6 Al 5 O 12 garnet as refrigerant.…”