Mohd. Nasir

Role of compensating Li/Fe incorporation in Cu0.945Fe0.055−xLixO: structural, vibrational and magnetic properties

Doped transition metal oxides, like CuO, are spintronic materials. An increase of magnetic moment has been reported in Fe-doped CuO. Additional secondary doping elements such as Li may further modify magnetism in transition metal oxides due to changes in valence state and size. Such complex doping may generate secondary impurity phases, restricting the success of such applications. Enhancement of magnetic properties strengthens applicability of the materials in devices. Single phase monoclinic Cu0.945Fe0.055−xLixO crystalline powders without any impurity are synthesized. Structural studies, electronic valence state, fine structure, and local geometry of constituent elements confirm the purity of the materials and provide clues to probable reasons leading to enhanced magnetism. Ferromagnetic coupling between neighboring spins is most likely dependent on the spin and separation between the spin species.

X-ray structural studies on solubility of Fe substituted CuO

CuO is a promising material for the spintronic industry for which lattice distortions/defects play an important role in determining its magnetic and various other physical properties. The ionic radii and charge of Cu2+[VI] (0.73 A) and Fe3+[VI] (0.64 A) are quite different. Hence high Fe substitution in CuO in place of Cu may generate strain/distortions. Fe substitution may enhance magnetic properties, even at room temperature, making such materials interesting for device applications. A detailed structural study on Fe incorporated CuO lattices to confirm phase purity, supported by evidence of the absence of a secondary phase is absolutely essential especially when considering a considerable substitution of up to ∼12.5%. The electronic valence state, fine structure and local neighborhood/geometry of constituent elements need to be investigated using synchrotron based X-ray absorption spectroscopy (XAS). We report, for the first time, such a detailed study on understanding this magnetically and electronically important material: Cu1−xFexO, 0 ≤ x ≤ 0.125.

Cu1–xFexO: hopping transport and ferromagnetism

Single phase, sol–gel prepared Cu1–xFexO (0 ≤ x ≤ 0.125) powders are characterized in terms of structural, electronic and magnetic properties. Using dielectric and magnetic studies we investigate the coupling of electron and spin. The electrical conductivities and activation energies are studied with increasing Fe content. Modelling of experimental conductivity data emphasizes a single hopping mechanism for all samples except x = 0.125, which have two activation energies. Hole doping is confirmed by confirming a majority Fe3+ substitution of Cu2+ in CuO from X-ray photoelectron spectroscopy studies (XPS). Such a substitution results in stabilized ferromagnetism. Fe substitution introduces variation in coercivity as an intrinsic magnetic property in Fe-doped CuO, and not as a secondary impurity phase.

Dielectric relaxation behavior in La1.80Y0.20NiMnO6 double pervoskite

Among multifunctional La2BB’O6 (B/B’ are transition metals) double perovskites, La2NiMnO6 has recently received significant attention due to its rich physics and prospects in technological applications. In the present study, La1.80Y0.20NiMnO6 was synthesized using sol-gel method. Le Bail profile analysis of room temperature X-ray diffraction data emphasized on the formation of single phase monoclinic (P21/n) La1.80Y0.20NiMnO6 ceramics. Temperature dependent dielectric spectroscopy shows relaxor-like behavior with giant dielectricity of the order of ∼104.