Improving the magnetic and dielectric properties of Cu1−Ho FeO2 nanoceramics by tuning the vacancy defects and Fe valence state

In this study, Cu1−xHoxFeO2 nanoceramics were synthesized by sol-gel method to investigate the influence of the vacancy defects and Fe valence state tuning on the magnetic and dielectric properties of Cu1−xHoxFeO2 nanoceramics. XRD and Raman analysis indicated that Cu1−xHoxFeO2 nanoceramics with single-phase delafossite structure were synthesized by sol-gel method; Ho3+ ions had replaced the Cu ions in CuFeO2 and resulted in lattice deformation. XPS analysis indicated that Ho3+ substitution could tune the Fe valence state, but did not cause significant change in oxygen vacancy concentration. The results of positron annihilation lifetime spectroscopy revealed that cation vacancies concentration in the interface region could be effectively tailored by Ho3+ substitution. The magnetic measurements indicated that Ho3+ substitution enhanced the magnetic transition temperatures and magnetization of Cu1−xHoxFeO2 samples, which could be mainly attributed to the cation vacancies concentration in the interface region and Fe2+ concentration. Most interestingly, the Cu1−xHoxFeO2 nanoceramics exhibited giant dielectric characteristic, which was attributed to the charge ordering of Fe3+ and Fe2+.