Large magnetocaloric effect in free-standing Gd₂O₃ nanostructures near liquid helium boiling point

Abstract Magnetic and magnetocaloric properties of free-standing gadolinium oxide (Gd 2 O 3 ) nanostructures have been studied. Nanoparticles of Gd 2 O 3 (Gd 2 O 3 -NP), nanorods of Gd 2 O 3 (Gd 2 O 3 -NR) and a mixed system of Gd 2 O 3 nanosheets and nanorods (Gd 2 O 3 -NS+NR) have been prepared by template-free methods without the use of any surfactant or a catalyst. These samples crystallize in cubic crystal structure (space group Ia- 3, no. 206, cI 80). Magnetization data indicate typical paramagnetic behavior in the temperature range of 300 K to 5 K for all the samples. All three Gd 2 O 3 nanostructures display large magnetocaloric effect at temperatures below ∼10 K. While the maximum isothermal magnetic entropy change (ΔS m ) value at 6 K is about −22.6 Jkg −1 K −1 for the Gd 2 O 3 nanorods and −17.8 Jkg −1 K −1 for Gd 2 O 3 nanoparticles for a magnetic field change of 70 kOe, the mixed Gd 2 O 3 nanosheets and nanorods system prepared by wet chemical method shows a maximum ΔS m value of −23.6 Jkg −1 K −1 for the same field change. These are about 41% to 89% more than that of bulk Gd 2 O 3 . Therefore, Gd 2 O 3 -based nanostructures could be very useful for low temperature magnetic refrigeration applications.