Abstract
Branchlike nickel oxide nanocrystals with narrow size distribution are obtained by a solution growth method. The size-dependent of magnetic properties of the nickel oxides were investigated. The results of magnetic characterization indicate that the NiO nanocrystals with size below 12.8 nm show very weak ferromagnetic state at room temperature due to the uncompensated spins. Both of the average blocking temperature (Tb) and the irreversible temperature (Tirr) increase with the increase of nanoparticle sizes, while both the remnant magnetization and the coercivity at 300 K increase with the decrease of the particle sizes. Moreover, the disappearance of two-magnon (2M) band and redshift of one-phonon longitudinal (1LO) and two-phonon LO in vibrational properties due to size reduction are observed. Compared to the one with the spherical morphological, it is also found that nano-structured nickel oxides with the branchlike morphology have larger remnant magnetization and the coercivity at 5 K due to their larger surface-to-volume ratio and greater degree of broken symmetry at the surface or the higher proportion of broken bonds.
Highlights
Nanostructured materials have been extensively investigated for the fundamental scientific and technology interests due to their significant in both fundamental research and applications
It was proposed that the binding of inert lithium stearate (LiSt) to the surfaces of NiO nanocrystals can prevent their in situ reduction into Ni, as our previous report.[15]
Nickel oxide nanocrystals with various size from 4.6 nm to 12.8 nm can be directly obtained by a solution growth method; these nanoparticles have a unique morphology with narrow size distribution, which can accurate reflect the magnetic properties in this size
Summary
Nanostructured materials have been extensively investigated for the fundamental scientific and technology interests due to their significant in both fundamental research and applications. Magnetic nanoparticles have been studied owing to their unique physical properties as compared to their bulk counterparts.[1]. In this context, antiferromagnetic nanoparticles have attracted significant interest due to their enhanced surface and interface effects, and the much lower core moment with respect to ferromagnetic particles of same size. Which can accurate reflect the magnetic properties in its size, can provide more comprehensive and deeper understanding of magnetic properties in this material This motivated us to perform systematic investigations on the magnetic properties of NiO nanocrystals with narrow size distribution. The results of magnetic characterization indicate that both of the average blocking temperature (T b) and the irreversible temperature (T irr) increase with the increase of nanoparticle sizes, while both the remnant magnetization and the coercivity at 300 K increase with the decrease of the particle sizes
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