Effect of Cu and B Co-doping on magnetocaloric effect, phase transition, and mechanical properties of Mn_(1.05)Fe_(0.9)P_(0.5-x)Si_(0.5)Cu_(0.10)B_x alloys

摘要

With large entropy changes and flexible preparation processes, (Mn, Fe)_2(P, Si) alloys have attracted wide interest from researchers for magnetic refrigeration. Cu doping can compensate for the mechanical properties, but will increase thermal hysteresis (△T_(hys)) and decrease the Curie temperature (T_C) of (Mn, Fe)_2(P, Si) alloys. To tune the T_C to room temperature while maintaining low thermal hysteresis and good mechanical properties, Cu-B co-doping is applied to (Mn, Fe)_2(P, Si) alloys. The results demonstrated that as the amount of B increases in Mn_(1.05)Fe_(0.9)P_(0.5-x)Si_(0.5)Cu_(0.10)B_x alloys, the T_C continuously increases from 261 K to 344 K, and the △T_(hys) decreases by 76%. Contour plots of XRD patterns show the shifts in Bragg angles near the Curie temperature, which are ascribed to the increase in the lattice parameters during phase transitions, leading to high internal stress. After long-term annealing, Cu tends to segregate at the grain boundaries to act as a buffer between the Fe_2P-type main phase. Therefore, stress from lattice deformation during first-order phase transitions can be absorbed. This study presents a new technical route to obtain magnetic refrigeration materials with high magnetocaloric effects and good mechanical properties by co-doping Cu and B, which is instructive for engineering applications.