Improving the magnetic and dielectric properties of Cu1_xHoxFeO2 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 nano -ceramics. 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 spec-troscopy 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 tran-sition 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+.