Magnetocaloric effect in frustrated magnetic oxides

In this work, two rare earth borates, REBO3 (RE = Gd, Yb), were synthesized using the traditional solid-state method. Both compounds crystallize in a monoclinic structure belonging to space group C2/c. The magnetism and magnetocaloric effect of REBO3 compounds have been studied through isothermal magnetization, magnetic susceptibility, and specific heat measurement. No obvious long-range order in either GdBO3 or YbBO3 compounds can be found at the low-temperature T >= 2 K in susceptibility and specific heat curves, suggesting a paramagnetic-like behavior at low temperatures. However, these compounds exhibit weak short-range antiferromagnetic couplings at low temperatures, as indicated by the Curie-Weiss fitting and magnetic susceptibilities under varying applied fields. The calculated value of magnetic entropy change -Delta Sm reaches the maximum value of 10.8 J mol- 1 K- 1 for a field change from 0 to 7 T at 2 K for GdBO3, and YbBO3 is 4.9 J mol- 1 K- 1. However, GdBO3 shows an adiabatic temperature change (Delta Tad) of 3.3 K and 7.9 K for field changes of 0-3 T and 0-7 T, respectively. Furthermore, we found that, in the liquid helium temperature range, GdBO3 is a more competitive magnetocaloric material than YbBO3. These results indicate the presence of distinct magnetic anisotropy for various rare-earth ions, as shown by isothermal magnetization and heat capacity measurements, which suggests that REBO3 is a promising system for studying a variety of magnetic ground states.