Structural and paramagnetic resonance properties correlation in lanthanum ion doped nickel ferrite nanoparticles

La³⁺ ion doped in nickel nanoferrite with different compositions were prepared by sol-gel route and characterized by different techniques. La³⁺ ions substitution induces dislocation and deformity in lattice to soften the lattice. XRD patterns confirmed the polycrystalline nature of nanoparticles with no extra phase as per JCPDS card no. 071–1232 with increase in lattice constants on substitution of larger ionic radii La³⁺ ions at Fe³⁺ sites. ν₁ Fe-O stretched vibrations of A- (Tetrahedral) and ν₂ Fe-O of B- (Octahedral) complexes are observed at 598 cm⁻¹ and 419 cm⁻¹ respectively in IR transmission graphs. The broadening of both stretching vibrational modes with La³⁺ ion content is attributed to the reduction in grain size arising from the lattice distortion by cation distribution, interactions among nanoparticles and La³⁺ ion concentration. On increasing La³⁺ ion concentration, the variations in the intensity of ν₁band are more pronounced as compared to ν₂band which confirms the preferred substitution of La³⁺ ion at octahedral site by expanding the B-site radii. FESEM micrographs exhibit the homogeneous and agglomerated nanoparticles pattern of these doped analogues. EPR spectra exhibit broad ferromagnetic signal with no characteristic peak of SPM feature. The peak to peak line width and g-value increases on increasing La³⁺ ion concentration in samples. These morphological and magnetic properties can be exploited for their use in the development of stable ferrofluid for heat sink application and as sensing electrode in chemical/bio sensors.