Synthesis of a new class of high-entropy nitride ceramics and the effects of nitrogen vacancies on their magnetic properties

Abstract

This research prepared a new type of (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)N0.956 high-entropy nitride (HEN) ceramic powder with a cubic single-phase zinc blende structure using the (Co,Cr,Fe,Mn,Ni)3O4 high-entropy spinel oxide as raw material through ammonia nitridation. Nitrogen vacancies are the main feature of HENs, considerably influencing the HEN their structure and magnetic properties. (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)N0.864 HENs with nitrogen vacancies were synthesized through hydrogenation. Theoretical calculations and experimental characterization results show that the samples obtained by heat treatment at 300 °C for 30 min in Ar/H2 atmosphere have the most nitrogen vacancies. Nitrogen vacancies affect the interactions among metal ions in the crystal, resulting in the spin tilt of some divalent metal ions requiring more energy; thus, coercivity (Hc) decreases from 411.98 to 251.40 Oe, and saturation magnetization (Ms) increases from 5.71 to 8.09 emu/g. We offer a fresh viewpoint to explain the structural origin of magnetic characteristics in high-entropy ceramics based on the theoretical calculations of the association between defects, structure, and magnetism as well as the characterization data.