Ni_0.4Cu_0.2Zn_0.4Tb_xFe_2-xO₄ nanospinel ferrites: Ultrasonic synthesis and physical properties

The Fe³⁺ ions were replace with Tb³⁺ ions as highly paramagnetic rare earth element within the structure of Ni_0.4Cu_0.2Zn_0.4Fe₂O₄ nano-spinel ferrites (NSFs). The structural, magnetic, spectroscopic and optic properties have been studied in details. All products have been synthesized via ultrasonic approach via Qsonica ultrasonic homogenizer, frequency: 20 kHz and power: 70 W for 60 min. No annealing or calcination process was applied for any product. The microstructural analysis of products has been done via X-ray powder diffractometry (XRD) which presented the cubic spinel structure with nanosized distribution of all. The cubic morphology of all products were confirmed by both HR-TEM and FE-SEM. Optical band gap (E_g) values were assessed by applying %DR (percent diffuse reflectance) analysis and Kubelka-Munk theory. The Tauc schemes showed that E_g values are in a narrow range (1.87-1.98 eV). The quadrupole splitting, line width, hyperfine magnetic field, isomer shift values and cation distribution have been determined from ⁵⁷Fe Mossbauer analysis. The magnetic properties of various nanoparticles have been obtained from VSM (vibration sample magnetometer) measurements at 10 and 300 K (RT). The magnetic results revealed superparamagnetic and soft ferromagnetic traits at 10 and 300 K, respectively. M_s (saturation magnetization) and M_r (remanence) initially increase with increasing Tb³⁺ substituting level up to x = 0.06 then diminish for further x values. H_c (coercivity) shows an opposite variation tendency of M_s and M_r. The observed magnetic traits are deeply discussed in relation with the structure, morphology, magnetic moments and cation distributions.