Large magnetocaloric effects due to the coincidence of martensitic transformation with magnetic changes below the second-order magnetic phase transition in Mn1-xFexCoGe

The magnetic properties, phase transitions, and related magnetocaloric effects in Mn1-xFexCoGe (x=0.12, 0.13) have been studied using magnetization and differential scanning calorimetry measurements. Instead of single first-order magnetostructural transition, two-step transitions have been detected in our studied system: one is second-order character followed by a first-order phase transition at lower temperature. The observed first-order phase transition as dominated by the crystallographic transition arises due to the coincidence of martensitic transformation with magnetic changes below the second-order magnetic phase transition in Mn1-xFexCoGe. Large magnetic entropy changes (-ΔSM) have been observed in our studied system due to a first-order phase transition between two high magnetization states. The estimated value of -ΔSM for x=0.12 (-ΔSM=16.5 J/kg K for ΔH=5 T around 242 K) is comparable to the giant-magnetocaloric materials, such as Gd5Si 2Ge2 and MnFeP0.45As0.55, which undergo a disorder-to-order magnetostructural transition. © 2012 Elsevier B.V. All rights reserved