Magnetic structure and magnetocalorics ofGdPO4

Abstract

The magnetic ordering structure of GdPO 4 is determined at T = 60 mK by the diffraction of hot neutrons with wavelength λ = 0.4696Å. It corresponds to a noncollinear antiferromagnetic arrangement of the Gd moments with propagation vector k = (1/2,0,1/2). This arrangement is found to minimize the dipole-dipole interaction and the crystal-field anisotropy energy, the magnetic superexchange being much smaller. The intensity of the magnetic reflections decreases with increasing temperature and vanishes at T ≈ 0.8 K, in agreement with the magnetic ordering temperature T N = 0.77 K, as reported in previous works based on heat capacity and magnetic susceptibility measurements. The magnetocaloric parameters have been determined from heat capacity data at constant applied fields up to 7 T, as well as from isothermal magnetization data. The magnetocaloric effect, for a field change B = 0 − 7 T, reaches − S T = 375.8 mJ/cm 3 K −1 at T = 2.1 K, largely exceeding the maximum values reported to date for Gd-based magnetic refrigerants.

Effect of Gd polarization on the large magnetocaloric effect ofGdCrO4in a broad temperature range

“…Third, the exchange interaction between 3d ions, usually much higher than the R-R exchange interaction, provides an internal field, increasing the polarization of the R ions below the ferromagnetic ordering temperature. The Cr 5+ ion plays an important role as the promoter of the interactions in the rare-earth sublattice, increasing its ordering temperatures at least one order of magnitude in comparison with the analogous RXO 4 (X = P, As, V), where X is a diamagnetic element [24,25]. The case R = Gd is easier to analyze because, for this spin-only atom, the anisotropy and crystal-field energies are of the order of 1 K or less [24], therefore, a higher MCE is expected.…”

Enhanced cryogenic magnetocaloric effect in Eu8Ga16Ge30 clathrate nanocrystals

“…On the other hand, several compounds and intermetallic alloys, such as Ho 5 Pd 2 , DyAl 2 , HoCo 2 , ErCo 2 , HoNiSi, HoRu 2 Si 2 , and GdPO 4 , have been reported to show large MCE at low temperature and are therefore promising for cryogenic magnetic refrigeration. [1][2][3][4][5] It should be noted that these intermetallic alloys possess a relatively low resistivity, thus causing huge eddy current losses when used in actual magnetic cooling devices. Some also exhibit considerable thermal and magnetic hysteresis losses which are undesirable for active magnetic refrigeration.…”

“…[1][2][3][4][5][6] One major emphasis for the research in this area is to find refrigerant materials exhibiting a large MCE in different temperature regimes, from room temperature to cryogenic temperatures. Two distinct temperature ranges of practical interests are near room temperature and below liquid nitrogen temperature (the so-called cryogenic temperature range).…”

Enhanced Magnetocaloric Effect from Cr Substitution in Ising Lanthanide Gallium Garnets Ln3CrGa4O12 (Ln = Tb, Dy, Ho)

“…[13] Of these, gadolinium gallium garnet (GGG), which shows no long-range ordering down to 25 mK, has been established as a MCM for magnetic refrigeration in the liquid helium temperature regime. The absence of long-range ordering, high density of magnetic ions, chemical stability, and lack of single ion anisotropy (L = 0 for Gd 3+ ) allowing for the full magnetic entropy (Rln[2J + 1] = 17.29 J K −1 mol Gd −1 ) to be extracted in high magnetic fields makes it an ideal MCM for T < 20 K. [14][15][16] In recent years, a number of Gd containing MCMs with better performance at 2 K have been reported [17][18][19][20] but GGG continues to be used and serves as the benchmark for MCMs in this temperature regime. However, for all the Gd-based magnetocalorics, the change in magnetic entropy is maximized in fields of 5 T or higher.…”

“…) to be extracted in high magnetic fields makes it an ideal MCM for T < 20 K. [14][15][16] In recent years, a number of Gd containing MCMs with better performance at 2 K have been reported [17][18][19][20] but GGG continues to be used and serves as the benchmark for MCMs in this temperature regime. However, for all the Gd-based magnetocalorics, the change in magnetic entropy is maximized in fields of 5 T or higher.…”