Synthesis and characterization of Ni2+- Zr4+ doped Ba-Ca M-type hexaferrites using sol-gel auto-combustion method

Abstract

This work aims to study the effect of Zr-Ni dopant on the structure and traits of M-type barium calcium hexaferrites (BaCaM). For the first time, Ba_0.8Ca_0.2Zr_xNi_xFe_12–2xO₁₉ (0.0 ≤ x ≤ 1.0) samples are synthesized employing the SGACM (sol-gel auto-combustion method). The pure phase formation of BaCaM was established by XRD data Rietveld refinement. An augmentation in both the lattice parameters (‘a’ as well as ‘c’) owing to the higher ionic radii of dopant ions as compared to Fe³⁺ shows that Ni²⁺and Zr⁴⁺ions were successfully swapped with Fe^3⁺. The "c/a" ratio lies between 3.93–3.96 disclosing that the synthesized materials possess an M-type hexagonal ferrite structure. The reduction in crystallite with an increase in doping level might be due to lattice strain generated by the larger size of Ni²⁺ and Zr⁴⁺ dopant ions. The presence of two bands in the wavenumber range of 400 to 880 cm^-1 in FTIR spectra corresponds to the Fe–O stretching in octahedral and tetrahedral locations. The Raman peaks widen without any shifting of the peak with an increment in Ni²⁺-Zr⁴⁺ ions contents revealing that Ni²⁺-Zr⁴⁺ are incorporated into BaCaM without changing its crystal structure. According to the M-H plots M_s value enhance from 24.94 (x = 0.00) to 36.84 emu/g (x = 0.60) and beyond x = 0.60, M_s values drop with an increment in Ni²⁺-Zr⁴⁺substitution level. A broad coercivity range lies between 4858 Oe (x = 0.0) to 653 Oe (x = 1.0), decreasing monotonically with substitution in Ni²⁺-Zr⁴⁺. All the synthesized material exhibits a reduction in dielectric constant value as frequency increases. Ni-Zr-doped BaCaM materials could be a suitable candidate for magnetic recording media and microwave absorber applications.