1,721,235 research outputs found
Highlights of the R&D activities in the nanotechnology area performed by the Italian Interuniversity Consortium on Materials Science and Technology (INSTM)
No full textThe Italian Interuniversity Consortium on Material Science and Technology (INSTM) is actually participated by 44 Italian Universities thus realizing an integrated scientific network among the community of chemists and engineers. INSTM is involved in many strategic areas for innovative devices development, such as: molecular materials for electronics and photonics; polymeric, composite, metallic and ceramic materials for structural and/or functional applications; nano-materials; nano-biomaterials and protective coatings. Research and development activities are performed through projects funded by public and private Italian institutions and International institutions, such as the European Commission. In the recent years much effort has been put to develop fundamental and applied knowledge in the area of nanotechnology and nanostructured materials. In this frame INSTM is actually coordinating three European Networks of Excellence and is participating in different Integrated Projects. A summary related to some of the on-going R&D activities is reported
Magnetic Exchange Coupling in the FeIII6(μ6-O) Core: A Hint to the Magnetic Properties of Higher-Nuclearity Spin Clusters
No full textVariable-temperature magnetic susceptibility measurements performed on two hexairon(III) clusters containing a μ6-oxo bridge show that this unusual bridging mode leads to weak antiferromagnetic exchange-coupling interactions between the metal centers, with J(trans) and J(cis) values of 19(2) and 9(1) cm-1, respectively. The result is relevant to the search for magneto-structural correlations in oxo-bridged polyiron aggregates
Single-molecule Magnets Based on Iron(III) Oxo Clusters
No full textPolynuclear compounds of magnetic transition metal ions are attracting large interest after the discovery that their magnetisation may relax very slowly at low temperature. Since their behaviour is similar to that of bulk magnets they may be called single molecule magnets. Here we review the magnetic properties of iron(III) clusters showing such features which may be interesting for future applications, as well as strategies for designing new molecules with increased performances
New Experimental Techniques for Magnetic Anisotropy in Molecular Materials
No full textMagnetic anisotropy is a very important property in magnetochemistry. Its knowledge allows us to obtain a fundamental understanding of the electronic structure of both simple paramagnetic species and of magnetically coupled systems. The difficulties associated with its experimental determination have so far limited its investigation. Recently new experimental techniques using superconducting quantum interference devices (SQUID) and micro-SQUID arrays as well as cantilever torque magnetometry have drastically reduced the size of the crystals needed for the measurements, thus opening new perspectives. We will briefly review here these techniques, with the aim to advertise their use in the chemical community
Organizing and Addressing Magnetic Molecules
No full textMagnetic molecules ranging from simple organic radicals to single-molecule magnets (SMMs) are intensively investigated for their potential applications in molecule-based information storage and processing. The goal of this Article is to review recent achievements in the organization of magnetic molecules on surfaces and in their individual probing and manipulation. We stress that the inherent fragility and redox sensitivity of most SMM complexes, combined with the noninnocent role played by the substrate, ask for a careful evaluation of the structural andelectronic properties of deposited molecules going beyond routine methods for surface analysis. Detailed magnetic information can be directly obtained using X-ray magnetic circular dichroism or newly emerging scanning probe techniques with magnetic detection capabilities
Nonadiabatic Landau Zener Tunneling and Quantum Phase Interference in Fe-8 Molecular Nanomagnets
No full textThe Landau-Zener method allows to measure very small tunnel splittings Δ in mol. clusters Fe8. The obsd. oscillations of Δ as a function of the magnetic field applied along the hard anisotropy axis are explained in terms of topol. quantum interference of two tunnel paths of opposite windings. Studies of the temp. dependence of the Landau-Zener transition rate P gives access to the topol. quantum interference between excited spin levels. The influence of nuclear spins is demonstrated by comparing P of the std. Fe8 sample with two isotopically substituted samples. The need of a generalized Landau-Zener transition rate theory is shown
Structure and Magnetic Properties of a Dodecanuclear Twisted-ring Iron(III) Cluster
No full text[Fe(OMe)2(dbm)]12 (I; Hdbm = dibenzoylmethane) was prepd. by the reaction of FeCl3 with Hdbm in presence of KOMe or CsOMe in anhyd. MeOH. I.6CHCl3 is monoclinic, space group P21/c, Z = 4, R = 0.0967, Rw = 0.3174. Each Fe(III) in I has a distorted octahedral environment with 6 O atoms from methoxide and dbm with Fe-O band lengths of 1.94-2.07 Å, forming a twisted ring which is not planar and has C1 point group symmetry. NMR data of I in presence of NaBPh4 or LiBPh4 indicate that I is quant. converted to hexairon(III) coronates, [MFe6(OMe)12(dbm)6]+. Magnetic susceptibility data indicate antiferromagnetic coupling in I between high-spin Fe(III) atoms
Magnetism of Large Iron-Oxo Clusters
No full textThe role of large iron-ore clusters in chemistry, material science, and fundamental physics is briefly reviewed. Examples of clusters with nuclearity ranging from 6 to 19 are reported as well as their magnetic properties. Relevant topics, such as the role of spin topology and spin frustration in antiferromagnetically coupled systems and the observation of superparamagnetic like behaviour and molecular hysteresis, are discussed. The use of strong magnetic fields in the characterization of magnetic clusters is emphasized and a theoretical approach for the rationalization of the magnetic properties of clusters is briefly reported
Spin Dynamics in Mesoscopic Size Magnetic Systems: A H-1 NMR Study in Rings of Iron(III) Ions
No full textTwo magnetic mol. clusters contg. almost coplanar rings of iron (III) ions with spin S = 5/2 were studied by 1H NMR and relaxation measurements. The 1st system, which will be referred to as Fe6, is a mol. [NaFe6(OCH3)12(C17O4H15)6]+ClO4- or [NaFe6(OCH3)12(C15H11O2)6]+ClO4- or [LiFe6(OCH3)12(C15H11O2)6]+ClO4- while the 2nd type of ring, denoted Fe10, corresponds to the mol. [Fe10(OCH3)20(C2H2O2Cl)10]. The 1H NMR linewidth is broadened by the nuclear dipolar interaction and by the dipolar coupling of the protons with the iron (III) paramagnetic moment. The nuclear spin-lattice relaxation rate, T1-1, of the proton is a sensitive probe of the Fe spin dynamics. In both clusters, T1-1 decreases with decreasing temps. from room temp., goes through a peak just .ltorsim.30 K in Fe6 and 10 K in Fe10, and it drops exponentially to very small values at helium temp. The temp. dependence of the relaxation rate is discussed in terms of the fluctuations of the local spins within the allowed total spin configurations in the framework of the weak collision theory to describe the nuclear relaxation. The authors use the calcd. energy levels for the Fe6 ring based on a Heisenberg Hamiltonian and the value of J obtained from the fit of the magnetic susceptibility to describe semiquant. the behavior of T1-1 vs. T. The exponential drop of T1-1 at low temp. is consistent with a nonmagnetic singlet ground state sepd. by an energy gap from the 1st excited triplet state. The values obtained for the gap energies are ET/k = 12 K for Fe10 and ET/k = 38 K for Fe6 which are almost twice as big as the values deduced from susceptibility measurements. At all temps. the relaxation rate decreases with increasing magnetic field, i.e., NMR resonance frequency. This effect could be related to the long time persistence of the spin correlation functions typical of diffusive modes in low dimensional magnetic systems. It is argued that the data presented are a direct exptl. study of spin dynamics in mesoscopic spin rings and should afford a test for exact anal. and/or numerical solns
NMR investigation of Gd(hfac)3NITEt fully frustrated helimagnet
No full textThe family of the quasi-1D molecular magnetic chains Gd(hfac)3NITR (where hfac is hexafluoro-acetylacetonate and NITR is 2-R-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-l-oxyl 3-oxyde) have assumed a great importance in the study of molecular magnets in the last 10 years. These chains develop along b crystallographic axis and consist in a regular pattern of Gd(hfac)3 moieties (S_Gd=7/2) alternated to nitronyl-nitroxide organic radicals NITR (R = iPr, Et, Ph, Me) (srad=1/2). In these derivatives the shortest interchain distance is about 10.5Å and, as a consequence, the ratio between interchain and intrachain exchange interactions is Jinter/Jintra1.9K while just below the transition temperature T(c)^3D=1.9K becomes suddenly much larger (>1 MHz), due to the insurgence of a local field Hloc at protons sites, generated by the ordered arrangement of the electronic spins
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