Correlating tailored saturation magnetization of normal-inverse spinels with noncollinear magnetic ordering

Nanoparticles of NiFe 2 O 4 (NF) and Ni 0.5 Zn 0.5 Fe 2 O 4 (NZF) were synthesized via the citrate precursor method. Analysis of X-ray diffraction (XRD) data revealed the single phase, crystallinity, and spinel structure of the NF and NZF nanoparticles with a crystallite size of ~ 12 nm and ~ 33 nm, respectively. The prominent (311) peaks of the XRD patterns were analyzed to determine various other crucial microstructural parameters of the nanoparticles. Rietveld structural refinements were conducted to reveal the crystal lattice imperfections through values of R-factor (weighted profile), R-factor (expected), and goodness-of-fit index ( χ 2 ). Scanning electron microscope and transmission electron microscope micrographs confirmed crystalline nanoparticles with clear grain boundaries and random agglomeration. The as-sintered NF and NZF nanoparticles exhibited moderate specific saturation magnetization ( σ s ) (34.12 emu/g and 53.55 emu/g) and low coercivity ( H c ) (7.75 Oe and 62.19 Oe), respectively. The observed decline in σ s for the prepared nanoparticles compared to their bulk counterparts was correlated with a nontrivial deviation of the magnetic ordering from the conventional Néel’s two-sublattice model. These deviations suggested that the magnetic order of both the NF and NZF nanoparticles followed Yafet–Kittel three-sublattice model with a split octahedral sublattice and triangular spin arrangement. The noncollinearity and canted spin arrangement of magnetic ions of the octahedral sublattices were confirmed by significant values of spin canting angles of NF (39.10°) and NZF (55.81°) nanoparticles.