Improvement of magnetocaloric properties around Néel temperature in a polycrystalline system of Dy-substituted YMn2O5

Abstract

This paper deals with the magnetic and magnetocaloric characteristics of Dy-substituted YMn₂O₅ (Y_1−xDy_xMn₂O₅) with x values between 0.6 and 1, which were prepared through sol–gel method. X-ray diffraction and Raman measurements attest well the high quality of our polycrystalline samples, which crystallize in an orthorhombic structure. The vibrational properties of all detected modes at room temperature were identified by measuring and comparing the Raman phonon frequencies to the lattice dynamics calculations. As expected, magnetic study reveals that magnetization was enhanced by the substitution of Y³⁺ by Dy³⁺. The Dy-substituted YMn₂O₅ sets the Néel transition [T_N(Mn)] in the temperature range from 40 to 45K favoring the emergence of a transition at a very low temperature due to the long-range ordering of the Dy³⁺ magnetic moments below 13K [T_N(Dy)]. Dual peaks in the magnetic entropy change curve are observed being in good agreement with magnetization data, which enlarges the range of application of these materials. On the other hand, a large magnetocaloric effect is observed close to 13K which is mainly due to the ordering of Dy³⁺ magnetic moments. Also, the incommensurate antiferromagnetic transition of Mn magnetic moment taking place around 40K affects slightly the entropy change. Our investigation revealed that the refrigerant capacity (RC) of polycrystalline samples is greater compared to the average RC values for a, b, and c axes of single-crystal samples such as HoMn₂O₅ and TbMn₂O₅.