Enhancement of the refrigerant capacity in low level boron doped La0.8Gd0.2Fe11.4Si1.6

The effects of boron doping on the itinerant-electron metamagnetic (IEM) transition and the magnetocaloric effects (MCEs) in the cubic NaZn13-type La0.8Gd0.2Fe11.4Si1.6 compound have been investigated. The Curie temperature, TC, of La0.8Gd0.2Fe11.4Si1.6Bx compounds with x=0, 0.03, 0.06, 0.2 and 0.3 was found to increase from 200 K to 222 K with increase in boron doping, x. The maximum values of the isothermal magnetic entropy change, ΔSM, (derived using the Maxwell relation for a field change ΔB=0–5 T) in La0.8Gd0.2Fe11.4Si1.6Bx with x=0, 0.03, 0.06, 0.2 and 0.3 are 14.8, 16, 15, 7.5 and 6.6 J kg−1 K−1 respectively, with corresponding values of the refrigerant capacity, RCP of 285, 361, 346, 222 and 245 J kg−1. The large ΔSM values observed for the undoped sample, and the low level B doped La0.8Gd0.2Fe11.4Si1.6B0.03 and La0.8Gd0.2Fe11.4Si1.6B0.06 compounds are attributed to the first order nature of the IEM transition while the decrease of ΔSM at x=0.2 and 0.3 is due to a change in the second order phase transition with increase in B doping. The nature of the magnetic phase transitions is also reflected by the magnetic hysteresis of 3.7, 9, 5.7, 0.4 and 0.3 J kg−1 for x=0.0, 0.03, 0.06, 0.2 and 0.30 respectively. The possibility of tuning the TC and the magnetocaloric properties at temperatures close to room temperature make this system interesting from the points of view of both fundamental aspects as well as applications.

► Boron doping tunes TC towards higher temperatures.
► Tuning of magnetic phase transition from 1st order to 2nd order with increase in boron doping.
► Enhanced refrigerant capacity at low boron doping levels.
► Significant reduction of hysteresis at high boron doping levels.