Crystallographic and magnetic modulation via Sm3+-driven cation rearrangement in Co-Cr spinel ferrite nanoparticles for magnetic device applications
Sanskruti S. Kadam, Vipul More, Manisha R. Patil, Sagar E. Shirsath, Akash V. Fulari, Vishnu S. Shinde, S.S. Kammar, R.H. Kadam, A. B. Kadam
Abstract
Sm 3+ -substituted Co–Cr spinel ferrite, CoCr 0.2 Fe 1.8−x Sm x O 4 , nanoparticles with varying Sm concentrations (x = 0.0–0.1) were synthesized via the sol–gel auto-combustion method. XRD and Rietveld refinement confirmed a pure cubic spinel structure with lattice parameters increasing from 8.3840 to 8.3952 Å and crystallite sizes from 18.12 to 20.64 nm due to the larger ionic radius of Sm 3+ (0.964 Å). FTIR spectra revealed characteristic metal–oxygen vibrations in the 400–600 cm −1 range, with band shifts indicating structural distortion. Strain analysis using Williamson–Hall and size-strain plot methods showed a significant increase in tensile strain (from 0.296 × 10 −4 to 3.190 × 10 −4 ) and crystallite growth up to 22.51 nm. Cation distribution studies confirmed the preferential occupation of Sm 3+ at B-sites, inducing Fe 3+ redistribution and disrupting A–B superexchange interactions. Magnetization measurements exhibited a reduction in saturation magnetization (72.07 to 62.18 emu/g) and effective magnetic moment (3.03 to 2.72 μ B ), while coercivity increased from 277.7 to 324.2 Oe due to strain effects and spin–orbit coupling. The initial permeability also declined, reflecting enhanced anisotropy. These results establish a strong structure–property correlation and suggest that rare-earth doping is an effective strategy to engineer ferrites for advanced magnetic storage applications.