Novel route to prepare HoN nanoparticles for magnetic refrigerant in cryogenic temperature

Abstract

Holmium nitride (HoN) nanocrystallites were synthesized by a plasma arc discharge technique and characterized to study their magnetocaloric properties. HoN was formed under the influence of nitrogen–argon mixed gas. N2 gas was used as an active element for arc discharge between two electrodes maintained at a constant current. In addition, N2 gas played an important role not only as a reducing agent but also as an inevitable source of excited nitrogen molecules and nitrogen ions for the formation of HoN phase. The ratio of partial pressure between Ar and N2 was systematically varied to obtain single phase HoN with minimal impurities. Magnetocaloric properties were measured by applying fields up to 50 kOe in the temperature range from 6 K to 60 K. The as-synthesized HoN nanoparticles have shown a change in magnetic entropy of 27.5 J/kgK with a transition temperature at 14.2 K thereby demonstrating their ability to be applied as an effective low temperature magnetic refrigerant material towards the re-liquefaction of H2.