Effect of Cu substitution on the phase stability and magnetism in Ho4Co3-Cu compounds

The phase constitution, magnetic ordering, magnetic phase transition and magnetocaloric properties of the Ho ₄Co _{3- x}Cu _x ( x = 0, 0.07, 0.14 and 0.28) samples were investigated in detail. When the content of Cu is 0 and 0.07, the samples are composed of three phases, while a single Ho ₄Co ₃ phase is obtained when the Cu content reaches 0.14. The stability of the formation of the Ho ₄Co ₃ phase increased with increasing concentration of Cu. For the Ho ₄Co _2.86Cu _0.14 and Ho ₄Co _2.72Cu _0.28 compounds, it exhibits a ferromagnetic ordering around the Curie temperature 48 K. The isothermal entropy change (−Δ S _M) was calculated based on isothermal magnetization measurements using Maxwell`s relation. For an applied magnetic field change of 0–5 T, the maximum magnetic entropy change values were determined to be 11.8 J kg ⁻¹ K ⁻¹ for x = 0, 14.8 J kg ⁻¹ K ⁻¹ for x = 0.14 and 18.6 J kg ⁻¹ K ⁻¹ for x = 0.28, respectively, with the corresponding refrigerant capacity (RC) values of 576 J kg ⁻¹, 465 J kg ⁻¹, and 503 J kg ⁻¹. The considerable magnetocaloric effect indicated that a range of Ho ₄Co _{3- x}Cu _x alloys could be considered potential candidates for low-temperature magnetic refrigeration materials.