Large refrigerant capacity of RGa (R = Tb and Dy) compounds

Abstract

The magnetic properties and magnetocaloric effects (MCEs) of RGa (R = Tb and Dy) compounds are investigated. The TbGa compound exhibits two successive magnetic transitions: spin-reorientation (SR) transition at TSR = 31 K and second-order ferromagnetic (FM)–paramagnetic (PM) transition at Curie temperature TC = 154 K, while the DyGa compound undergoes a SR transition with TSR=25 K and a FM–PM transition with TC = 113 K. It is noteworthy that a broad distribution of the magnetic entropy change peak is observed. The values of the refrigerant capacity (RC) for TbGa and DyGa are found to be 620.6 and 381.9 J/kg for a field change of 0–5 T, respectively. And for a field change of 0–7 T, the values are 900 and 584.2 J/kg, respectively. The large value of RC for TbGa and DyGa originates from the combined contribution from SR and FM–PM transitions, which enlarges the temperature span of large MCE.

Large magnetocaloric effect of NdGa compound due to successive magnetic transitions

“…The values of ∆S M is smaller than that of ErGa and HoGa compounds, 26,29 but that is larger than TbGa and DyGa. 32 In addition, it is noted that the ∆S M is negative at 7.5 K, which is the typical result of AFM ground state as has been observed in other AFM materials. 41,42 Since there are two peaks on the ∆S M curves and one overlaps the other, the ∆S M almost keeps a constant value in a wide range of temperatures.…”

“…That is to say, both types of magnetic transitions contribute to MCE, which has been observed in other RGa (R=Gd, Tb, Dy, Ho, Er) compounds. 26,29,30,32,33 Analysis of Mössbauer spectra has shown that the rotation of the magnetic moments occurs in the ac-plane at low temperatures due to the competition between the exchange interaction and the interaction of the crystalline electric field in NdGa compound. 25,29 For polycrystalline NdGa compound, the applying of magnetic field will destroy the balance mentioned above.…”

“…25 studied the magnetic and MCE properties of RGa (R=Gd, Tb, Dy, Ho, Er) compounds. [29][30][31][32] Furthermore, the δT FWHM of ErGa compound was extended successfully by spin optimization. 33 In addition, interesting magnetic properties, transport properties and MCEs were also found in TmGa and PrGa compounds.…”

Spin-reorientation in DyGa

“…This Mössbauer work was extended by Delyagin et al [18] who observed spin-reorientation transitions in NdGa, GdGa, HoGa and ErGa. Recently, Zheng et al [8] reported an anomaly in the magnetisation data of TbGa and DyGa below the Curie temperature (T C ) ascribed to spinreorientation transitions (T SR ). Neutron diffraction determinations of the magnetic structures in the RGa series have been reported for TbGa [19], ErGa [20], HoGa [21], GdGa [22] and TmGa [16].…”

“…The RGa (R¼ rare earth) compounds have been known since the 1960s [1][2][3][4] and are enjoying a revival of interest due to their possible use in low-temperature magnetocaloric refrigeration applications [5][6][7][8][9][10][11][12]. They crystallise in the orthorhombic CrB-type Cmcm structure with both the R and Ga atoms occupying 4c sites with the m2m point symmetry.…”