Stability of the first-order character of phase transition in HoCo₂

HoCo₂ exhibits a giant magnetocaloric (MC) effect at its first-order magnetostructural phase transition around 77 K, and understanding the thermodynamic nature of this transition in response to external magnetic fields is crucial for its MC applications. In this study, we present a comprehensive investigation of specific heat and magnetization measurements of HoCo ₂ under varying magnetic fields. The specific heat measurements qualitatively indicate a transformation from first- to second-order behavior of this phase transition at higher magnetic fields. However, analysis of the power-law dependence of the magnetic entropy change (Δ<em>S</em>_M∝Hⁿ) and the breakdown of universal behavior in the temperature dependence of Δ<em>S</em>_M suggest that the first-order nature remains intact, even up to 7 T. This stability of the first-order nature is further manifested through the distinctive non-linear behavior of modified Arrott plots, with a negative slope in the 6–7 T range.. Authors: Kumar, Ajay [Ames Lab., and Iowa State Univ., Ames, IA (United States)] (ORCID:0000000208407951); Biswas, Anis [Ames Lab., and Iowa State Univ., Ames, IA (United States)] (ORCID:0000000317333082); Mudryk, Yaroslav [Ames Lab., and Iowa State Univ., Ames, IA (United States)] (ORCID:0000000326580413). DOE Contract: AC02-07CH11358. Subjects: 36 MATERIALS SCIENCE; Magnetic ordering; Magnetic susceptibility; Phase transitions; Polycrystalline material; Thermal effects; Thermodynamic properties