Ferromagnetic materials containing light elements, such as a"-Fe16N2, have attracted attention as ferromagnetic materials that do not contain rare-earth elements such as neodymium. Cation substitution has been attempted to control magnetism, but there are few examples of multi-cation substitution. The author has performed multi-cation substitution of Fe3O4, the synthetic raw material of a"-Fe16N2, to create light-element-containing multi-cation magnetic materials. The (Cr,Fe,Mg,Mn,Ni)3O4 spinel was successfully synthesized in a short time using microwaves as a synthesis method. In the poster, the authors will also report the results of magnetic synthesis using this high-entropy oxide as a raw material.