Large magnetic entropy change at cryogenic temperature in rare earth HoN nanoparticles

Abstract

The most extensive cooling techniques based on gases have faced environmental problems. So, tremendous effort has been devoted to developing an alternative cooling technique and the search for solid state materials that show a large magnetocaloric effect (MCE) at cryogenic temperature. In the present work, we report the synthesis of HoN nanoparticles by a plasma arc discharge method with different composition of N₂/H₂ gases and its effect on magnetocaloric properties. HoN prepared under gas compositions (N₂/H₂: 40/60, 60/40, 80/20, and 100% N₂) were structurally and morphologically characterized. The paramagnetic to ferromagnetic transition temperature T_C is observed to be 13.9, 14.2, 14.5 and 14.2 K for all samples, respectively. The magnetic entropy change (−ΔS_M) is found to be extended over a wide range of temperatures around T_C, and its maximum value at an applied magnetic field of 5 T is obtained to be 27.7, 29.8, 30.2 and 34.2 J kg⁻¹ K⁻¹ for all investigated samples, respectively. It is noted that the relative cooling power improved significantly from 555 to 632 J kg⁻¹ compared to 507 J kg⁻¹ K⁻¹ of bulk HoN. The larger MCE values obtained for HoN nanoparticles will be very useful for its cryogenic application.