The crystal structures, magnetic interactions and cryogenic magnetocaloric effects for NaGdXO₄ (X=Si, Ti) compounds

The development of ultra-low temperature magnetic refrigeration technologies demands magnetic refrigeration materials with excellent properties. Hence, improving performances of magnetic refrigerants has always been a significant scientific issue in magnetic refrigeration field. In this article, the relationship of crystal structures, magnetic interactions and magnetocaloric effect (MCE) for NaGdSiO₄ and NaGdTiO₄ has been investigated. NaGdSiO₄ and NaGdTiO₄ both crystallizes orthogonal structure, but the significant difference of unit cell parameters and symmetries results in different arrangement of Gd atoms. The distorted crystal structure and weaker magnetic between Gd³⁺ ions make NaGdSiO₄ exhibit larger MCE with the maximum magnetic entropy change (-∆S_M) of 49.0 J·kg⁻¹·K⁻¹ at 2.8 K. Comparably speaking, NaGdTiO₄, which is a quasi-triangular antiferromagnet, possesses a stronger magnetic interaction between Gd³⁺ ions with the maximum -∆S_M of 31.9 J·kg⁻¹·K⁻¹ at 2.6 K. These results confirm the importance of magnetic interactions for magnetic refrigeration materials, and, more broadly, they highlight the significance of crystal structures in that field.