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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.

The ground-state magnetic properties and related electronic properties of small Fe~clusters are calculated by using an spd-band model Hamiltonian in the unrestricted Hartree-Fock approximation. Results are given for the average magnetic moment per atom pN, the spin-polarized charge distribution within the cluster, and the sp and d electronic density of states. The calculated p~(N ( 15) are larger than the bulk value pg = 2.21@,. Small local sp magnetic moments are obtained, which in most cases are opposite to the dominant d magnetic moments (p, "-O. lpga, ps 2.5 -2. gpss).The role of sp electrons and spd hybridization is discussed particularly, by comparison with previous d-band model calculations. The main quantitative effect obtained by including the sp electrons in the self-consistent calculations is a reduction of about 10% of the value of P~.

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The transition from insulating small Hgn clusters to metallic bulk-Hg is studied using a parametrized LCAO model. Our results for the size dependence of the cohesive energy show that covalent bonding is already important for n = 13-19, indicating that the transition from Van der Waals to covalent bonding should take place near this cluster size range. For n ≳ 80 s- and p-bands overlap, the density of states resembles the bulk density of states and the gap at the Fermi-level is close to the limiting value Δn(n → ∞) = [N(εF)n]-1. Therefore, no important changes in the electronic structure occur for n > 80 and metallic-like optical properties similar to those observed for alkali-metal clusters are expected. For intermediate sizes (19 ≲ n ≲ 80) semiconducting like properties are expected. In qualitative agreement with experiment, we obtain for Hg-clusters an increase of the average bond-length of about 5% with respect to the bulk. The effects of electron correlations and surface relaxation are briefly discussed.