Jolaikha Sultana1
The University of Memphis1
Jolaikha Sultana1
The University of Memphis1
This study describes the synthesis and magnetocaloric properties of rare-earth chromite’s, viz., HoCrO<sub>3,</sub> Ho<sub>0.67</sub>Er <sub>0.33</sub>CrO<sub>3 </sub>and<sub> </sub>Ho<sub>0.67</sub>Er<sub>0.33</sub>Cr<sub>0.5</sub>Al<sub>0.5</sub>O<sub>3 </sub>orthochromites These materials are considered functional materials with interesting magnetic and magnetocaloric properties, making them suitable for potential applications in magnetic refrigeration. The samples were synthesized using facile sol-gel auto combustion method, As confirmed by X-ray diffraction analysis, the resulting compounds have a pure orthorhombic crystal structure with the space group Pbnm,. The lattice parameters and volume of the samples were observed to decrease with the substitution of Al<sup>3+</sup> ions. This decrease can be attributed to the smaller ionic radius of Al<sup>3+</sup> compared to Cr<sup>3</sup>. The bond angle and bond-length of Cr-O-Cr of studied compounds were observed to vary with the substitution, which observed to have influence on their magnetic and magnetocaloric properties. The magnetic measurements were performed using PPMS in the temperature range 5K -300K and field up to 5T. The temperature dependent magnetization curve shows magnetic transition at 141 K for HoCrO<sub>3</sub>, 135 K for Ho<sub>0.67</sub>Er <sub>0.33</sub>CrO<sub>3</sub>, and 35 K for Ho<sub>0.67</sub>Er<sub>0.33</sub>Cr<sub>0.5</sub>Al<sub>0.5</sub>O<sub>3</sub>, respectively. The magnetization and magnetic entropy change (ΔSm), determined from magnetic isotherms, were found to increase with the introduction of Er and Al doping. The maximum magnetic entropy change observed was 6.46 Jkg<sup>-1</sup>K<sup>-1</sup> for HoCrO<sub>3 </sub>, 8.04 Jkg<sup>-1</sup>K<sup>-1</sup> for Ho<sub>0.67</sub>Er <sub>0.33</sub>CrO<sub>3</sub>, and further increased to 9.70 Jkg<sup>-1</sup>K<sup>-1</sup> for Ho<sub>0.67</sub>Er<sub>0.33</sub>Cr<sub>0.5</sub>Al<sub>0.5</sub>O<sub>3 </sub>under an applied field of up to 5T. This enhancement in magnetization and magnetic entropy change is attributed to the Al<sup>3+</sup> substitution, which affects the Cr<sup>3+</sup> -Cr<sup>3+</sup> exchange coupling due to changes in the Cr1-O1-Cr1 bond angle and Cr1-O1 bond lengths.<br/>The study concludes that the co-doped chromite’s, particularly Er<sup>3+</sup> and Al<sup>3+</sup> co-doped HoCrO<sub>3</sub>, have not been previously reported in the literature. The observed magnetocaloric properties, especially in the Al<sup>3+</sup> doped samples, suggest their potential for low-temperature magnetic refrigeration applications.<br/><br/>Authors: Jolaikha Sultana, Christopher Hanley, Dr. Arjun K Pathak, and Dr. Sanjay R Mishra