The Fe₂P type Mn–Fe–P–Si alloys exhibit a giant magneto-elastic first-order transition, but the large hysteresis limits their performance. Crystal structure evolution and magnetocaloric performance were investigated by varying the Mn and Fe contents at a constant V substitution of 0.02 in Fe₂P-type (Mn_1.17-xFe_0.73-yV_0.02) (P_0.5Si_0.5) (where x + y = 0.02). The V substitution of Fe content shows a larger reduction of hysteresis compared with the same substitution amount of Mn content. During magnetoelastic phase transition, V-substitution reduces the volume change and the volumetric stresses, providing a superior mechanical stability. Compound with the V substitution of Fe (y = 0.02) shows the best magnetocaloric effect with a low thermal hysteresis of 0.6 K. Our developed Mn_1.17-xFe_0.73-yV_0.02P_0.5Si_0.5 alloys are excellent materials for room-temperature magnetic heat-pumping applications by using a permanent magnet.

@en

Large thermal hysteresis in the (Mn,Fe)2(P,Si) system hinders an efficient heat exchange and thus limits the magnetocaloric applications. Substitution of manganese by vanadium in the Mn1-x1Vx1Fe0.95P0.593Si0.33B0.077 and Mn1-x2Vx2Fe0.95P0.563Si0.36B0.077 compounds enable a significant reduction in the thermal hysteresis without losing the giant magnetocaloric effect. For the composition closest to the critical one, where first-order crossovers to second-order phase transition in the series of x2 = 0.02, Mn0.98V0.02Fe0.95P0.563Si0.36B0.077 exhibits a thermal hysteresis that is reduced from 1.5 to 0.5 K by 67%, yielding an adiabatic temperature change of 2.3 K and magnetic entropy change of 5.6 J/kgK for an applied field of 1 T, which demonstrates its potential for highly efficient magnetic heat pumps utilizing low-cost permanent magnets.@en

A rotary active magnetic regeneration refrigerator prototype named FAME Cooler was developed for studying the performance of different magnetocaloric materials in a realistic practical environment. The rotary magnetic field source generates an average magnetic field of 0.875 T within a volume of 0.71 l The regenerator is designed asymmetrically and holds in total 1.18 kg of gadolinium spheres for a first performance test. Combined with a real-time controlled programmable solenoid-valves system, different working parameters or thermodynamic cycles can be applied. In the performance test, while the temperature of system hot side was fixed at 295 K, under a utilization condition of 0.25, this prototype achieved a maximum zero-span cooling power of 162.4 W, and a zero-power temperature span of 11.6 K. Under a utilization condition of 0.15, a maximum COP of 1.85 was reached. These performance metrics are comparable with existing magnetic heat pump devices of the same scale.

@en