Influence of La content on magnetic properties of Cu doped M-type strontium hexaferrite: Structural, magnetic, and Mossbauer spectroscopy study

Highlights: • Invariance of lattice parameter with Cu²⁺ doping in SrM. • c-aix contraction with La³⁺-Cu²⁺ doping. • Preferential occupancy of Cu²⁺ for the 12k site. • Enhanced occupancy of Cu²⁺ at the 12k site in the presence of La³⁺ at Sr²⁺ site. • Marked improvement in saturation magnetization and coercivity in La³⁺-Cu²⁺ doped SrM. The present study investigates the influence of Cu²⁺ and La³⁺-Cu²⁺ doping on the magnetic properties of Sr_1−xLa_xFe_12−xCu_xO₁₉ (x = 0.0–0.5) hexaferrite (SrM) compounds. The samples were prepared via facile autocombustion technique followed by sintering. X-ray powder diffraction patterns show the formation of the pure phase of M-type hexaferrite for all x. Invariance in lattice parameters was observed with only Cu²⁺ substitution while lattice contraction along c-axis was observed with co-doping La³⁺-Cu²⁺ in SrM. The magnetic property of these compounds is explained based on Cu²⁺ occupancy in the absence and presence of La³⁺ in SrM magnetoplumbite structure. The Cu²⁺ doped SrFe_12−xCu_xO₁₉ sample showed a monotonic decrease in Ms value while La³⁺-Cu²⁺ showed a noticeable increase in Ms value with x. Furthermore, while coercivity of Cu²⁺ doped SrM reduced with x, the coercivity of La³⁺-Cu²⁺ doped SrM showed a marked 12% increase in coercivity at x = 0.1 (Hc = 4391 Oe) from that of x = 0.0 (3918 Oe). Interestingly, Cu²⁺ doped SrM displayed invariance in Tc ∼ 458.6 °C with x, while La³⁺-Cu²⁺ doping reduced Tc by 5% from its x = 0 (Tc = 451.9 °C) to 429.6 °C. The room temperature Mossbauer spectral analysis confirmed a Cu²⁺ preference for the 12k site and its occupancy is observed to be influenced by the presence of La³⁺ ion at the Sr²⁺ site.