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In this communication, we experimentally report, for the first time, that the MnO nanoclusters with cluster diameters of 5-10 nm show a ferromagnetic behavior with a phase transition from ferromagnetic to paramagnetic phases at 27 K even though their bulk phase is antiferromagnetic. We observed large coercivities up to 9500 Oe and a large remanence of 1.72 emu/g at 2 K, which are typically observed values for ferromagnetic materials. Although it is not clear, this abnormal ferromagnetic behavior of MnO nanoclusters may arise from cluster size effects.

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Comprehensive measurements of electron spin resonance were carried out on a La 0.7 Ca 0.3 MnO 3 single crystal over a wide temperature range covering the ferromagnetic as well as the paramagnetic phases. Our analysis of the asymmetric lineshapes indicates that the phase segregation of good and poor conducting regions persists far above the ferromagnetic-paramagnetic phase transition temperature.

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High temperature finite-size effects in the magnetic properties of Ni nanowires J. Appl. Phys. 112, 073906 (2012) Equilibrium magnetic states in individual hemispherical permalloy caps Appl. Phys. Lett. 101, 132419 (2012) Magnetic properties of Sm0.1Ca0.9MnO3 nanoparticles J. Appl. Phys. 112, 063921 (2012) Positive exchange bias and upward magnetic relaxation in a Fe-film/CoO-nanoparticle hybrid systemWe report fabrication of the arrays of ferromagnetic FeCo and FeCr binary nanocluster wires ͑NCWs͒ by thermally decomposing the Fe͑CO) 5 /Co 2 (CO) 8 and Fe͑CO) 5 /Cr͑CO) 6 metal carbonyl vapors, respectively, with a resistive heater placed in the middle of a pair of permanent disc magnets. The NCWs are produced through the pileup of binary nanoclusters along the lines of magnetic flux, perpendicular to the substrates attached to a pair of permanent disc magnet surfaces. For both arrays of FeCo and FeCr binary NCWs, the diameter of individual NCWs ranges from 8 to 20 nm and the NCWs exist as bundles with their length up to 2-3 mm. We observed compositional dependence of structure.

Either an S 8 symmetrical 48-membered hexadecanuclear or an S 10 symmetrical 60-membered icosanuclear manganese metallamacrocycle was self-assembled using a manganese ion and a ditopic pentadentate ligand. This was either N-4-phenylbenzoylsalicylhydrazide (H 3pbshz) containing a rigid rod-shaped, bulky biphenyl residue as a terminal N-acyl group or N-3,3-diphenylpropionylsalicylhydrazide (H 3dppshz) containing a flexible beta-branched N-acyl group, but with two sterically bulky phenyl residues at the Cbeta position. The backbone of these metal-organic assemblies is a repeating unit consisting of a -[Mn-N-N-] link that extends to complete either the 48-membered cyclic structure involving 16 manganese(III) centers and 16 ditopic linker ligands or the 60-membered cyclic structure involving 20 manganese(III) centers and 20 ditopic linker ligands (depending on the ligand used). Even though the nuclearity of the metallamacrocycles was different, the successive manganese centers were in the same chiral sequence, ...(LambdaLambdaDeltaDelta)(LambdaLambdaDeltaDelta)....

Grain boundaries (GBs) are defects in crystal structures, which are in general known to be highly active toward various electrocatalytic reactions. Herein, we identify the adverse behaviors of the GBs for bimetallic platinum–cobalt (Pt–Co) nanocatalysts in the oxygen reduction reaction (ORR). As model catalysts, GB-rich Pt–Co nanowires (Pt–Co GB-NWs) and single-crystalline Pt–Co nanowires (Pt–Co SC-NWs) are synthesized. They have very similar diameters, Pt-to-Co ratios, and Pt-rich surface structures, except for the GB populations, which can be precisely controlled by applying an external magnetic field during their synthesis. The presence of GBs in Pt–Co NWs promotes Co leaching at an applied electrochemical potential, inducing significant changes in the surface Pt-to-Co ratio. The resulting Pt–Co GB-NWs perform only half the ORR activity compared with the Pt–Co SC-NWs. As a result, it is revealed that the surface GB sites are deactivated by causing elemental leaching and may not act as an ORR promoter for the Pt–Co nanowire catalyst.