Cation-engineered Zn Ti co-substituted BaM Hexaferrites with enhanced magnetic and Magnetocaloric performance

Abstract

Tailoring the functional properties of M-type hexaferrites through controlled cation engineering has emerged as a powerful route for developing next-generation magnetic materials. In this work, Zn Ti co-substituted barium hexaferrites BaFe 12-2x Zn x Ti x O 19 (x = 0.0 and 0.2, BFZTO) were synthesized via a sol–gel auto-combustion method to examine the structural, microstructural, magnetic, and magnetocaloric effects induced by dual-cation substitution. X-ray diffraction patterns refined using the Rietveld method demonstrated that the samples crystallize solely in the magnetoplumbite structure (space group P63/mmc). Increasing the dopant level led to a marked reduction in crystallite dimensions, decreasing from about 89 nm to nearly 43 nm. SEM and TEM analyses further revealed well-defined hexagonal platelets and demonstrated that Zn Ti incorporation promotes finer grains and enhanced microstructural homogeneity.Raman spectroscopy further confirms the structural integrity and highlights Zn–Ti-induced local lattice distortions.Magnetic characterization indicated that introducing non-magnetic Zn 2+ and Ti 4+ ions weakens Fe–O–Fe superexchange interactions, resulting in a decrease in Curie temperature T C (740 → 690 K) and a moderate reduction in saturation magnetization M S (74.45 → 68.29 emu.g −1 ). In contrast, coercivity H C increased significantly (1.57 → 3.12 kOe), reflecting grain refinement and strengthened magnetocrystalline anisotropy. Law of Approach to Saturation analysis confirmed a notable enhancement in the effective anisotropy constant with higher substitution levels. Importantly, Zn Ti co-substitution considerably improved the magnetocaloric behavior: the maximum magnetic entropy change increased from −ΔS M max 1.85 to 2.18 J.kg −1 .K −1 , and the relative cooling power RCP max with rose from 158 to 247 J.kg −1 under a 10 T magnetic field. This enhancement is associated with dopant-induced lattice perturbations that broaden the magnetic transition and amplify spin-entropy variations near T C . Overall, this study shows that controlled Zn Ti co-substitution effectively tailors the magnetic properties of M hexaferrites, making them suitable for moderate-temperature magnetic refrigeration and rare-earth-free permanent magnet applications. • Zn Ti co-substituted BaM hexaferrites were successfully synthesized by sol–gel method. • Rietveld refinement confirms single-phase magnetoplumbite structure. • Zn Ti substitution refines grains and improves microstructural homogeneity. • Zn Ti co-substitution weakens Fe–O–Fe interactions, enhancing coercivity. • Magnetocaloric response is improved with higher entropy change and cooling power.