Exploring Magnetic XY Behavior in a Quasi-2D Anisotropic Triangular Lattice of Cu(II) by Functionalized Graphene.

Study on magnetism in two-dimensional (2D) spin-lattices is advancing rapidly. In this work, phase-pure botallackite (Bo) (Cu2(OH)3Br), a quasi-2D S = 1/2 anisotropic triangular spin-lattice is stabilized over 2D reduced graphene oxide (rGO) nanosheets via simple oxidation-reduction reaction chemistry. In comparison to polycrystalline Bo, such an anchoring resulted in the oriented growth of Bo crystallites in the Bo-rGO system. The Bo-rGO nanocomposite was found to be magnetically active with a Néel transition at ∼8.9 K, crossing over to possible XY anisotropy at ∼5 K-as revealed by complementary dc and ac susceptibility measurements-an unprecedented observation in the field assigned to an interfacial effect. This work demonstrates the potential usage of nonmagnetic 2D functionalized graphene to significantly modulate the magnetic properties of 2D spin-lattices.

Metamagnetism in Nanosheets of CoII-MOF with TN at 26 K and a Giant Hysteretic Effect at 5 K.

Herein, we have synthesized at room-temperature two-dimensional nanosheets of a MOF comprised of cobalt(II) ion with benzenedicarboxylic acid  ligand, which exhibited unusual magnetic properties. Direct-current magnetic susceptibility revealed an antiferromagnetic (AFM) transition at 26 K (Néel temperature,  TN) followed by a canting of the spin moments along with the concomitant appearance of a sigmoidal-shaped magnetization versus field ( M- H) curve at 15 K. Such a canted AFM ordering led to nonzero remnant magnetization with a remarkably high coercive field of ∼10 kOe at 5 K. Metamagnetism was further substantiated by the alternating-current magnetic susceptibility measurements.

Evolution and magnetic characteristics of NiO-Ni(OH)2 core-shell nanostructures.

The evolution and magnetic behaviour of NiO-Ni(OH)2 core-shell nanostructures with different thicknesses of the hydroxide shell have been studied. The nickel hydroxide shell is found to alter the magnetic characteristics of nickel oxide at low temperatures and explains the origin of the exchange bias effect due to the antiferromagnetic NiO core and a ferromagnetic nickel hydroxide shell.

Embedding S = 1/2 Kagome-like Lattice in Reduced Graphene Oxide.

An elegant platform to explore frustrated magnetism is the kagome spin lattice. In this work, clinoatacamite, a naturally occurring S = 1/2 kagome-like antiferromagnetic insulator, is synthesized in water at ambient pressure for the first time from a cuprous chloride (CuCl) precursor whereby Cu(I) was spontaneously oxidized to Cu(II) in the form of clinoatacamite [Cu2(OH)3Cl] with a simultaneous reduction of graphene oxide (GO) to reduced graphene oxide (rGO) in one pot. A stable nanocomposite of phase-pure clinoatacamite nanocrystals embedded in the rGO matrix was isolated. The clinoatacamite-rGO nanocomposite was determined to be magnetically active with a markedly enhanced coercive field of ∼2500 Oe at 5 K as well as electronically active with a conductivity value of ∼200 S·m-1 at 300 K. Our results illustrate an avenue of combining exotic magnetic and electronic lattices without impeding their individual characteristics and synergistically generating a new class of magnetic semiconductors.

Structural characterization and magnetic properties of undoped and copper-doped cobalt ferrite nanoparticles prepared by the octanoate coprecipitation route at very low dopant concentrations.

Nanoparticles of undoped and copper-doped cobalt ferrite Co1-x Cu x Fe2O4 at very low dopant concentrations (x = 0; 0.02; 0.04; 0.06; 0.08) were successfully synthesized by pyrolysis of the corresponding hetero metal octanoate precursors obtained via coprecipitation using the octanoate ligand as precipitating agent. The precursors were then characterized by FTIR, ICP-AES and TG-DTA analyses and the results reveal the formation of a copper-cobalt-iron hydroxooctanoate represented by the formula [Co1-x Cu x Fe2(C8H15O2)6(OH)2·2H2O]. The decomposition products obtained upon pyrolysis in air at 400 °C for 3 h were characterized by FTIR, XRD, SEM, TEM, XPS and VSM analyses. FTIR and XRD analyses showed the formation of a single phase mixed spinel ferrite while TEM analysis showed that the particles have a spherical shape with a mean size of 20 nm and form spherical agglomerates with sizes reaching 500 nm in some cases as the SEM images show. The chemical states of the metallic species in the samples were revealed by XPS to be Cu2+, Co2+ and Fe3+. These results combined with XRD confirmed the mixed spinel structure, Co1-x Cu x Fe2O4 in which Cu2+ ions substitute Co2+ ions in tetrahedral sites for x lower than 0.06 and in octahedral sites for x between 0.06 and 0.08. Magnetic parameters such as saturation magnetization (M s), coercivity (H c), remanent magnetization (M r), magnetocrystalline anisotropy constant (K) and reduced magnetization (M r/M s), obtained from magnetic hysteresis loops measured at room temperature, are in agreement with this mixed spinel structure and also indicate that these materials are ferromagnetic and could be good candidates for applications in biomedicine and in microwave devices.

Highly sensitive and fast responding CO sensor based on Co3O4 nanorods.

Co(3)O(4) nanorods (diameters approximately 6-8 nm and lengths approximately 20-30 nm) were synthesized for the first time through a simple co-precipitation/digestion method by calcination of cobalt hydroxyl carbonate in air and their CO gas sensing properties were investigated. The Co(3)O(4) nanorods exhibited outstanding gas sensing characteristics such as, higher gas response (approximately 6.55-50 ppm CO gas at 250 degrees C), extremely rapid response (approximately 3-4s), fast recovery (approximately 5-6s), excellent repeatability, good selectivity and lower operating temperature (approximately 250 degrees C). Furthermore, the Co(3)O(4) nanorods are able to detect up to 5 ppm for CO with reasonable sensitivity (approximately 3.32) at an operating temperature 250 degrees C and they can be reliably used to monitor the concentration of CO over the range (5-50 ppm). The experimental results clearly demonstrate the potential of using the Co(3)O(4) nanorods as sensing material in the fabrication of CO sensors. Plausible CO sensing mechanism of the Co(3)O(4) nanorods is also discussed.

Bacterial aerobic synthesis of nanocrystalline magnetite.

The synthesis of iron oxide nanoparticles of the predominantly magnetite phase by the reaction of aqueous iron complexes with the bacterium, Actinobacter spp., is described. This reaction occurs at room temperature and under aerobic conditions, resulting in the formation of superparamagnetic magnetite.