Homogeneous solid solutions of sol−gel-prepared R 2 NiMnO 6 (R = La, Pr, Nd, Sm, Gd, Tb, Dy, Y, and Ho) double perovskites crystallize in a B-site-ordered monoclinic structure (P2 1 /n space group). Monoclinic distortion enhances with decreasing R 3+ ionic radii (r R 3+ ). The magnetic ordering temperature (T C ) decreases from 270 K for La 2 NiMnO 6 to 80 K for Ho 2 NiMnO 6 as r R 3+ decreases from 1.16 Å (La 3+ ) to 1.02 Å (Ho 3+ ). An additional magnetic anomaly is observed in Nd 2 NiMnO 6 , Sm 2 NiMnO 6 , Tb 2 NiMnO 6 , and Dy 2 NiMnO 6 at lower temperatures, which originates from the 3d−4f coupling between Mn−Ni and Nd 3+ /Sm 3+ /Tb 3+ /Dy 3+ magnetic moments. Further, high saturation magnetization is achieved for all samples, indicating that they are atomically ordered and have less antisite disorders. Upon a decrease in the size of R 3+ , the local structure shows an expansion of NiO 6 octahedra and almost unchanged of MnO 6 octahedra. X-ray-absorption near-edge spectroscopy reveals a majority of Ni 2+ and Mn 4+ ions in all samples. Softening of phonon modes results in the elongation of the Ni/Mn−O bond length. Finally, a correlation among lattice parameters, structural distortion, octahedral tilting, superexchange angle, electronic band gap, Curie temperature, and the rare-earth ionic radius is established.

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The double perovskite La 2 FeMnO 6 is ideally expected to be a ferrimagnet with a low saturation moment of 1 µ B / f.u. Inhomogeneity in the Fe/Mn sites, along with other lattice disorders, can modify the exchange interactions in the material and result in a net saturation moment of more than 1 µ B / f.u. Here, the origin of complicated magnetic behavior is examined of a pure phase La 2 FeMnO 6 sample prepared by the sol-gel method. XRD analysis established that the material crystallizes in the orthorhombic Pbnm symmetry. The comprehensive analysis of x-ray photoelectron spectroscopy, x-ray near edge structure, and magnetic measurements acknowledge an antiferromagnetic coupling between Fe 3+ and Mn 3+ cations, thereby, resulting in the ferrimagnetic ground state for La 2 FeMnO 6 . The magnetic hysteresis loop obtained at 5 K shows a large coercivity of ∼820 Oe and a saturation moment of 1.6 µ B / f.u., hinting at partial B-site ordering in La 2 FeMnO 6 . The ac susceptibility and dc magnetization measurements indicate the existence of magnetic glassy states (of cluster-glass type) with two distinct dynamical freezing points at ∼27 and 92 K, along with a Griffiths-like phase in the material. The experimental results are discussed taking several possible exchange interactions among Fe 3+ and Mn 3+ ions in the system into consideration. The magnetic complexity of this system makes it attractive for fundamental research and technological applications.

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Among multifunctional double perovskite oxides, La2NiMnO6 has recently drawn significant attention due to its importance both in terms of understanding of fundamental physics and potential for device applications. The relative alteration in Ni:Mn ratio strongly influences the structural and magnetic properties of La2NiMnO6. The cation ratio and degree of cation order significantly affect the magnetic coupling of the two B‐site cations in these compounds. In the present study, La2Ni1−xMn1+xO6 (x = −0.25, 0, 0.25) samples with different Ni:Mn ratio have been prepared using sol–gel method and modifications of the above physical properties from that of a stoichiometric sample of La2NiMnO6 are discussed. The crystalline structures of the samples varied with different ionic ratios. While all samples exhibited ferromagnetic behavior, long‐range Ni/Mn magnetic ordering was detected in selected samples only. The experimental values of saturation magnetization were smaller than the theoretical spin‐only moments, which suggests a less ordered state for all samples. Due to an increased antiferromagnetic interaction caused by antisite disorders, the saturation magnetization decreases while the coercive field increases with decreasing Mn content.

Monoclinic single phase Cu0.945Fe0.055−xLixO, with Cu2+ properly substituted by Fe3+ and Li1+, shows enhanced magnetic moment with stronger FM coupling due to Li1+ doping.

SXAS/XANES/EXAFS studies indicate absence of Fe-clusters/FeO/Fe2O3 impurity phases, confirm substitution of Cu2+ by Fe3+ in CuO lattice, and reveal similarity between Fe & Cu environments with reduction in O-vacancies for increasing Fe content.

The pure and Fe-doped CuO nanoparticles of the series Cu(1−x) Fe(x)O (x = 0, 0.027, 0.055, 0.097 and 0.125) were synthesized by a simple low temperature sol–gel method. Synthesized samples were characterized by a series of techniques including Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray electron spectroscopy (EDX), Diffuse Reflectance Spectroscopy (DRS), Fourier Transform Infrared Spectroscopy (FTIR), Hall Effect Set-up and Current–Voltage (I–V) characteristics. FESEM analysis shows formation of disc type structure increasing in grain size with Fe concentration in CuO. EDX confirmed the incorporation of iron in CuO. FTIR results of pure and Fe doped CuO samples have confirmed the formation of monoclinic CuO. The optical band gap estimated using Diffuse Reflectance Spectroscopy (DRS) shows the increment in the band gap values with Fe substitution. The Hall measurements show predominantly p-type conduction in all the samples and carrier densities decrease with increased Fe substitution. I–V characteristics of pure and Fe doped CuO nanoparticles show rectification behaviour of Schottky diodes.