Properties Of Co Clusters Research Articles

Hybrid ionic/electronic interphase enabling uniform nucleation and fast diffusion kinetics for stable lithium metal anode

Lithium (Li) dendrite issue, which is usually caused by inhomogeneous Li nucleation and fragile solid electrolyte interphase (SEI), impedes the further development of high-energy Li metal batteries. However, the integrated construction of a high-stable SEI layer that can regulate uniform nucleation and facilitate fast Li-ion diffusion kinetics for Li metal anode still falls short. Herein, we designed an artificial SEI with hybrid ionic/electronic interphase to regulate Li deposition by in-situ constructing metal Co clusters embedded in LiF matrix. The generated Co and LiF both enable fast Li-ion diffusion kinetics, meanwhile, the lithiophilic properties of Co clusters can serve as Li-ion nucleation sites, thereby contributing to uniform Li nucleation and non-dendritic growth. As a result, a dendrite-free Li deposition with a low overpotential (16.1 mV) is achieved, which enables an extended lifespan over 750 h under strict conditions. The full cells with high-mass-loading LiFePO4 (11.5 mg/cm2) as cathodes exhibit a remarkable rate capacity of 84.1 mAh/g at 5 C and an improved cycling performance with a capacity retention of 96.4% after undergoing 180 cycles.

Theoretical study of structural, electronic and magnetic properties of Co clusters embedded in an Ag matrix

We present a theoretical study investigating small Co nano-clusters embedded within an Ag matrix using Density Functional Theory. The calculations were conducted using the freely distributed SIESTA code, employing the generalized gradient approximation for the exchange and correlation potential. Our study focuses on Com clusters of specific sizes (m = 1 to 6, 8, 10, 13, and 19) embedded in an Ag bulk matrix. Our results reveal that the embedded Co clusters exhibit a magnetic signal distinct from that of the Co-bulk system. The calculated structural and electronic properties provide the following insights: (a) The Co clusters exhibit a preference for segregated and compact structures within the Ag matrix, with segregation prevailing over the mixing process; (b) The CoAg system demonstrates magnetic behavior across all Co cluster sizes, displaying a smooth decrease as the size increases, eventually approaching the magnetic value of Co in bulk; (c) The transfer of charge between Ag and Co is negligible. Theoretical results derived from our calculations offer a microscopic understanding of the physical processes occurring within the system. We hope that our findings will inspire experimental groups to verify and validate our observations.

From vanishing interaction to superferromagnetic dimerization: Experimental determination of interaction lengths for embedded Co clusters

We report on the magnetic properties of Co clusters (around 2.5 nm diameter) embedded in different matrices (C, Au, and Cu). Firstly, we accurately determine the intrinsic magnetic properties of the particles, using highly diluted samples where no interactions are detected, and a procedure relying on the theoretical description of various magnetometry measurements, and we show how both the magnetic size and anisotropy can be impacted by the nature of the matrix. Then, by considering nanoparticle assemblies of increasing concentrations, we investigate the effects of interactions between particles. In order to account for the observed evolution of the measurements, we propose a simple model where magnetic dimers are formed for distances lower than a given interaction length (of the order of one nanometer). This superferromagnetic correlation, which can be consistently inferred for each matrix, modifies the magnetic size distribution, which has a drastic effect as soon as particles are close enough to each other.

Magnetism of cobalt nanoclusters on graphene on iridium

The structure and magnetic properties of Co clusters, comprising 26–2700 atoms, self-organized or not on the graphene/Ir(111) moiré, were studied in situ with the help of scanning tunneling microscopy and x-ray magnetic circular dichroism. Surprisingly, the small clusters have almost no magnetic anisotropy. We find indication for a magnetic coupling between the clusters.

Magnetic anisotropy of embedded Co nanoparticles: Influence of the surrounding matrix

We report on the magnetic properties of Co clusters embedded in four different matrices (Ag, Au, Si, and amorphous carbon). The recently developed triple fit method for treating conventional magnetometry data allows, together with micro-superconducting quantum interference device (mu-SQUID) investigations, the detailed study of the influence of the surrounding matrix on the magnetic volume and the magnetic anisotropy of Co nanoparticles. While interdiffusion between matrix and Co atoms cannot be excluded in Si and amorphous C matrices, the structure of clusters embedded in the metallic matrices remains intact. Ag and Au matrices increase significantly the magnetic anisotropy energy of the Co clusters. mu-SQUID experiments indicate that the magnetic anisotropy of embedded clusters is not affected by a magnetically dead layer and that an anisotropy dispersion must be taken into account for size-selected nanoparticles.

Spin polarization and charge transfer of Co nanoclusters coated with CO molecules

We have investigated magnetic properties of Co clusters coated with CO molecules by first-principles density functional calculations. Total magnetic moment of the system decreases with the increase of CO molecule concentration regardless of adsorption sites for CO molecules. Spin polarization slightly increases as CO molecules are adsorbed on the most stable sites of Co cluster, which is caused by the increased local spin polarization of p-electrons due to charge transfer from Co clusters to CO molecules.

Magnetic properties of Co clusters deposited on Pt(111)

Using the fully relativistic version of the Korringa–Kohn–Rostoker method for electronic structure calculations within local spin density functional theory, the magnetic and spectroscopic properties of Co clusters deposited on Pt(111) have been investigated. Of central interest was the role of spin–orbit coupling, since it influences the spontaneous formation and orientation of magnetic moments and gives rise among other things to the occurrence of orbital magnetic moments, magnetic anisotropy energy and magnetic circular dichroism in X-ray absorption. The results have been complemented by calculations of the exchange coupling parameters Jij used within Monte Carlo simulations on the basis of the extended classical Heisenberg Hamiltonian. This allowed us to simulate the magnetic properties at finite temperatures, which are of central importance for applications.

Magnetic properties of Co clusters deposited on Pt(111) and Au(111)

The fully relativistic KKR method has been applied within the framework of spin density functional theory (SDFT) to calculate the electronic and magnetic properties of Co clusters deposited on a Pt(111) and a Au(111) surface, respectively. The influence of spin–orbit coupling on the formation and orientation of the magnetic moments, the central issue of our investigations, was studied for clusters of different size and shape. The results have been complemented by calculations of the exchange coupling parameters Jij which have been used within Monte Carlo simulations on the basis of the extended classical Heisenberg–Hamiltonian. This allowed simulation of the magnetic properties at finite temperatures, which are of central importance for technical applications of magnetic clusters.

Numerical study of the structure and the magnetic properties of Co clusters on Au surfaces

We model the growth process and the evolution of the magnetic behavior of Co clusters on Au surfaces in the case of low temperature co-deposition of Co and Au atoms and in the case of room temperature deposition of Co atoms on reconstructed Au(111) surfaces. The magnetic structure is obtained in either case by a Monte Carlo simulation, which includes exchange and magnetostatic (dipolar) intercluster interactions and perpendicular anisotropy for each Co cluster. Our simulations show an enhancement of the magnetization remanence that in the case of co-deposition is correlated with the annealing conditions and in the case of the deposition on the Au surface with the amount of deposited Co. The numerical results interpret experimental findings on these systems. An important finding of the experimental work confirmed by the numerical modeling is that these Co/Au structures show the way to control magnetic properties of clusters deposits over a large range of values. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic properties of cobalt clusters embedded in copper

The magnetic properties of Co clusters of up to several hundred atoms embedded in a Cu matrix are studied using an improved tight-binding model previously developed. We find that the average local spin moment for Co grains in Cu tends to be slightly larger for larger grains, and unlike the free clusters, the local spin moment on Co tends to decrease toward the Co/Cu interface. However, both for free and Cu coated Co clusters, the local orbital moment on Co always increases away from the center.

Magnetic characterization of granular Co/Al 2O 3 multilayers

We study the magnetic properties of Co clusters with diameters between 0.8 and 3 nm prepared by sequential sputtering of Co and Al 2O 3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data. Comparing this to the distribution of activation energies, obtained from the AC susceptibility, we have determined accurately the effective anisotropy constant K eff. We find that K eff is enhanced with respect to the bulk value and it increases as the average particle size decreases.

Magnetism of Co clusters embedded in Cu( [formula omitted]) surfaces: an ab initio study

We report calculations of electronic structure and magnetic properties of Co clusters (up to 50 atoms) embedded in Cu( 0 0 1 ) surfaces, performed using the first-principles linear muffin tin orbital-atomic sphere approximation method, implemented directly in real space. Co agglomerates of different sizes and shapes are considered in order to investigate the influence of the local environment around the Co sites to the magnetism in this class of systems. We find that the magnitude of the Co moments is mainly governed by two factors: the position of the site relative to the Cu( 0 0 1 ) surface layer and the number of Cu neighbors. The results show moment enhancement for sites located above the surface and/or placed substitutionally in the surface layer, due to their reduced coordination numbers. For sites with the same coordination number, the moment tends to decrease as the number of Cu neighbors increases. As a consequence, in Co agglomerates, the magnetic moment decreases considerably as one goes from more central sites to those close to the grain boundary at the Co–Cu interface.

Magnetic properties of self-assembled Co clusters on Au(111) below the ferromagnetic phase transition

We report on the magnetic properties of Co clusters grown on Au(111) in the cluster-size range from 300 to 12000 atoms. These clusters are superparamagnetic at room temperature, while at low temperatures blocking of the thermal fluctuations leads to a macroscopic remanence. The hysteresis curves measured in situ by means of x-ray magnetic circular dichroism show that the blocking temperature scales with cluster size, following a finite-size scaling power-law behaviour. We find that the blocking temperature of these clusters is substantially reduced by a thin silver overlayer, indicating a reduction in the perpendicular magnetic anisotropy at low coverages. With this change in anisotropy a clear change in the shift exponent can be observed.