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 -ΔS_m 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 (ΔT_ad) 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.