Magnetic properties and magnetocaloric effect of TbDyHoErM (M = Ti, Co) high entropy alloys

Magnetic rare earth high entropy alloy (HEA) TbDyHoEr is a candidate material for magnetic refrigeration due to its ideal ‘table-like’ magnetocaloric effect (MCE). In order to further enhance the MCE and reduce the amount of rare earth, TbDyHoErM (M = Ti, Co) were prepared by adding 3d transition metals Ti and Co with the same hexagonal close-packed (HCP) structure to the TbDyHoEr matrix. The addition of Ti does not change the HCP structure of matrix, and maintains excellent ‘table-like’ MCE of the matrix. The magnetic entropy change (ΔS_M) and refrigeration capacity (RC) value of TbDyHoErTi are 6.66 J·kg⁻¹ K⁻¹ and 779.22 J·kg⁻¹, respectively. After the addition of Co, a new phase R₃T (R = rare earth) was preferentially formed, and TbDyHoErCo is composed of R₃T phase and HCP disordered solid solution. This mixture structure raises the ΔS_M of TbDyHoErCo to 11.32 J·kg⁻¹ K⁻¹, but the RC value drops to 482.66 J·kg⁻¹ due to the disappearance of ‘table-like’ effect. The results not only provide direction for reducing the amount of rare earth, but also provide new choices for practical medium temperature magnetic refrigeration applications, which can be used in natural gas liquefaction, biological organ storage in medicine and quantum computer heat dissipation.