다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Electrical current can be completely spin polarized in a class of materials known as half-metals, as a result of the coexistence of metallic nature for electrons with one spin orientation and insulating nature for electrons with the other. Such asymmetric electronic states for the different spins have been predicted for some ferromagnetic metals--for example, the Heusler compounds--and were first observed in a manganese perovskite. In view of the potential for use of this property in realizing spin-based electronics, substantial efforts have been made to search for half-metallic materials. However, organic materials have hardly been investigated in this context even though carbon-based nanostructures hold significant promise for future electronic devices. Here we predict half-metallicity in nanometre-scale graphene ribbons by using first-principles calculations. We show that this phenomenon is realizable if in-plane homogeneous electric fields are applied across the zigzag-shaped edges of the graphene nanoribbons, and that their magnetic properties can be controlled by the external electric fields. The results are not only of scientific interest in the interplay between electric fields and electronic spin degree of freedom in solids but may also open a new path to explore spintronics at the nanometre scale, based on graphene.

https://arxiv.org/pdf/cond-mat/0611600.pdf

Half-metallic graphene nanoribbons

5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

The density-matrix renormalization group (DMRG) is a numerical algorithm for the efficient truncation of the Hilbert space of low-dimensional strongly correlated quantum systems based on a rather general decimation prescription. This algorithm has achieved unprecedented precision in the description of one-dimensional quantum systems. It has therefore quickly become the method of choice for numerical studies of such systems. Its applications to the calculation of static, dynamic, and thermodynamic quantities in these systems are reviewed here. The potential of DMRG applications in the fields of two-dimensional quantum systems, quantum chemistry, three-dimensional small grains, nuclear physics, equilibrium and nonequilibrium statistical physics, and time-dependent phenomena is also discussed. This review additionally considers the theoretical foundations of the method, examining its relationship to matrix-product states and the quantum information content of the density matrices generated by the DMRG.

http://www.physics.udel.edu/~bnikolic/QTTG/NOTES/DMRG/SCHOLLWOCK=RMP_dmrg.pdf

The density-matrix renormalization group

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

http://web.physik.uni-rostock.de/cluster/publ/BanSSR05.pdf

Magnetic and structural properties of isolated and assembled clusters

The size and structural dependence of magnetic properties of small ${\mathrm{Cr}}_{\mathrm{n}}$, ${\mathrm{Fe}}_{\mathrm{n}}$, and ${\mathrm{Ni}}_{\mathrm{n}}$ clusters are determined by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. Results are given for the average magnetic moment \ensuremath{\mu}${\ifmmode\bar\else\textasciimacron\fi{}}_{n}$, local magnetic moments, and magnetic ordering at T=0. We obtain for ${\mathrm{Fe}}_{\mathrm{n}}$ (n\ensuremath{\le}15) that \ensuremath{\mu}${\ifmmode\bar\else\textasciimacron\fi{}}_{n}$ varies as a function of n due to the interplay between the changes in coordination number and bond length as a function of cluster size, which may be related to recent experiments. The dependence of the structural cluster stability on magnetism is discussed. Results are also given for the cohesive energy, average bond length, and local densities of states.

Size and structural dependence of the magnetic properties of small 3d-transition-metal clusters.

Magnetic anisotropy of 3d transition-metal clusters.

The magnetic anisotropy energy (MAE) of $3d$ transition-metal wires is calculated self-consistently as a function of length, width, structure, and $d$-band filling. One-dimensional infinite chains show MAE's which are an order of magnitude larger than in two-dimensional thin films. A further enhancement is often obtained by reducing the chain length $l$ ( $l\ensuremath{\le}20$ atoms). The MAE of multichains (ladders) oscillates as a function of chain width and depends strongly on the transversal structure. The easy axis of Co wires changes from in-line to off-plane after deposition on Pd(110). Ladders and deposited chains show important in-plane anisotropies.

Magnetic Anisotropy of One-Dimensional Nanostructures of Transition Metals

Depositing pre-formed gas-phase nanoparticles, whose properties can be widely varied, onto surfaces enables the production of films with designed properties. The films can be nanoporous or, if co-deposited with an atomic vapour, granular, allowing independent control over the size and volume fraction of the grains. This high degree of control over the nanostructure of the film enables the production of thin films with a wide variety of behaviour, and the technique is destined to make a significant contribution to the production of high-performance magnetic materials. Here we review the behaviour of magnetic nanoparticle assemblies on surfaces and in non-magnetic and magnetic matrices deposited from the gas phase at densities from the dilute limit to pure nanoparticle films with no matrix. At sufficiently low volume fractions (~1%), and temperatures well above their blocking temperature, nanoparticle assemblies in non-magnetic matrices show ideal superparamagnetism. At temperatures below the blocking temperature, the magnetization behaviour of both Fe and Co particles is consistent with a uniaxial intra-particle magnetic anisotropy and an anisotropy constant several times higher than the bulk magnetocrystalline value. At relatively low volume fractions (≥5%) the effect of inter-particle interactions becomes evident, and the magnetization behaviour becomes characteristic of agglomerates of nanoparticles exchange coupled to form magnetic grains larger than a single particle that interact with each other via dipolar forces. The evolution of the magnetic behaviour with volume fraction is predicted by a Monte-Carlo model that includes exchange and dipolar couplings. Above the percolation threshold the films become magnetically softer, and films of pure clusters have a magnetic ground state that obeys the predicted magnetization behaviour of a correlated super-spin glass characteristic of random anisotropy materials. Magnetic nanoparticles in non-magnetic matrices show giant magnetoresistance behaviour, and the magnetotransport in deposited nanoparticle films is reviewed. Assembling Fe nanoparticles in Co matrices and vice versa is a promising technique for producing magnetic materials with a saturation magnetization that exceeds the Slater–Pauling limit. Structural studies reveal that the particles' atomic structure is dependent on the matrix material, and it is possible to prepare Fe nanoparticles with an fcc structure and, unusually, Co particles with a bcc structure. We also look to the future and discuss applications for materials made from more complex bi-metallic and core–shell nanoparticles.

https://iopscience.iop.org/article/10.1088/0022-3727/38/22/R01/pdf

G. M. Pastor

Papers

Magnetic and structural properties of isolated and assembled clusters

Size and structural dependence of the magnetic properties of small 3d-transition-metal clusters.

Magnetic anisotropy of 3d transition-metal clusters.

Magnetic Anisotropy of One-Dimensional Nanostructures of Transition Metals

The behaviour of nanostructured magnetic materials produced by depositing gas-phase nanoparticles