Effect of Co doping at the Ho– and Fe–sites on the structural, optical and magnetic properties of HoFeO₃ nanoparticles synthesized by co–precipitation method

This study investigates the effects of Co doping at the Ho– and Fe–sites in HoFeO₃ (HoFeO₃, Ho_0.9Co_0.1FeO₃, and HoFe_0.9Co_0.1O₃) on the elemental, structural, thermal, optical, and magnetic properties of nanosized perovskite–like HoFeO₃. Thermogravimetric analysis (TGA) revealed that Co doping at the Ho–site resulted in a greater reduction in mass upon calcination compared to doping at the Fe–site. Co doping at the Ho–site led to oxygen deficiency, while the sample with Co doping at the Fe–site and the undoped HoFeO₃ sample exhibited an oxygen redundant in the perovskite structure. Additionally, Co doping at the Ho–site reduced the average crystallite size and unit cell volume compared to the other samples. The Ho_0.9Co_0.1FeO₃ sample exhibited increased visible light absorption, with a narrower band gap (E_g = 1.94 eV) than that of the undoped HoFeO₃ (E_g = 2.13 eV) and HoFe_0.9Co_0.1O₃ (E_g = 1.98 eV) samples. Both the Co–doped samples showed hard ferromagnetism. Specifically, the coercivity (H_c = 1042.13 Oe) and remanence (M_r = 1.34·10⁰ emu·g⁻¹) of the Ho_0.9Co_0.1FeO₃ sample were 8 and 46 times higher, respectively, than those of the HoFe_0.9Co_0.1O₃ sample (H_c = 130.02 Oe, M_r = 2.92·10⁻² emu·g⁻¹).