The present paper reports the interconnection between cation distribution and physical properties of Co1−xNixFe2O4 (0 ≤ x ≤ 1) samples to tune them for suitable applications at room temperature. A set of five Co1−xNixFe2O4 (CNFO) samples with different nickel concentration (x) were prepared by using citrate-based ‘sol-gel’ method. The x-ray diffraction (XRD), Raman spectroscopic and scanning electron microscopic techniques were employed to characterize the samples structurally and morphologically. The Rietveld refinement of diffraction data confirms the monophasic spinel cubic structure with space group. The cationic arrangement between the tetrahedral (A-) and octahedral (B-)sites of (AB2O4-type) CNFO samples was estimated from the diffraction intensities of XRD and the spectral peaks of Raman data. Based on the cation arrangement, the estimated magnetic moment values, by adopting Neel’s sublattice model, were in correlation with each other and found to reduce with the rise in nickel content. A systematic change in the lattice, spectral and magnetic parameters with an increase in nickel content in CNFO, clearly ensures the transformation from hard to soft magnetic behavior of the samples. The marked magnetic transformation was elucidated in the framework of cation distribution. The tuning of magnetic parameters and cation distribution in ferrites with an appropriate element substitution might be a viable approach to make them for desired high-frequency magnetic applications.

The present work reports the effect of particle size and shape of CoFe2O4 (CFO) nanoparticles on magnetic properties and their use in device applications as permanent magnets at room temperature. A set of CFO samples with different particle sizes and shapes were synthesized via the polymeric method by sintering at temperatures ranging from 300 °C to 1200 °C. These materials were characterized structurally by x-ray diffraction, morphologically by scanning electron microscopy, and microstructurally by transmission electron microscopy. The morphology of these CFO samples shows size-dependent shapes like spherical, pyramidal, lamellar, octahedral and truncated octahedral shapes for the particle sizes ranging from 7 to 780 nm with increasing sintering temperature. The emergence of magnetic properties was investigated as a function of particle size and shape with a special emphasis on permanent magnet applications at low and room temperatures. The values of saturation and remanent magnetization were found to increase monotonously with a particle size up to 40 nm and from thereafter they were found to remain almost constant. The other magnetic parameters such as coercivity, squareness ratio, anisotropy constant and maximum energy product () were observed to increase up to 40 nm and then decreased thereafter as a function of particle size. The underlying mechanism responsible for the observed behavior of the magnetic parameters as a function of particle size was discussed in the light of coherent rotation, domain wall motion and shape induced demagnetization effects. The significant values of - the figure of merit of permanent magnets - observed for single domain particles (particularly, 14 nm and 21 nm) were found to have suitability in permanent magnetic technology.

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Magnetic dilution of a well-established Kitaev candidate system is realized in the substitutional Ru 1−x Rh x Cl 3 series (x = 0.02-0.6). Optimized syntheses protocols yield uniformly doped single crystals and polycrystalline powders that are isostructural to the parental α-RuCl 3 as per x-ray diffraction. The Rh content x is accurately determined by the quantitative energy-dispersive x-ray spectroscopy technique with standards. We determine the magnetic phase diagram of Ru 1−x Rh x Cl 3 for in-plane magnetic fields from magnetization and specific-heat measurements as a function of x and stacking periodicity and identify the suppression of the magnetic order at x ≈ 0.2 towards a disordered phase, which does not show any clear signature of freezing into a spin glass. Comparing with previous studies on the substitution series Ru 1−x Ir x Cl 3 , we propose that chemical pressure would contribute to the suppression of magnetic order, especially in Ru 1−x Ir x Cl 3 , and that the zigzag magnetic ground state appears to be relatively robust with respect to the dilution of the Kitaev--Heisenberg magnetic lattice. We also discovered a slight dependence of the magnetic properties on thermal cycling, which would be due to an incomplete structural transition.