D-Cems on iron films on silicon and PTFE: Effects of ion bombardment in the electronic stopping region

Depth-selective Mössbauer measurements were performed on as evaporated and proton bombarded iron films grown on PTFE and silicon single crystals. The results contribute to the understanding of the phenomena induced at the film/substrate interface by ion bombardment in the electronic stopping region.     

Surface modifications for mechanical applications

Chemical and high energy beam conversion coatings, as well as PVD thin films, are characterised to correlate microstructures and mechanical properties. In particular, thermochemical boriding and laser surface melting are considered to produce conversion coatings on iron alloys, and physical vapour techniques to deposit thin films of titanium nitride on iron. The mechanisms leading to selected microstructures and, consequently, to improved surface and interface properties are discussed.     

On the interface between iron and thin films of titanium and titanium nitride

Very thin films of TiN and Ti/TiN were prepared by physical vapor deposition on iron at 500°C to investigate the phenomena occurring at the coating/substrate interface during deposition. By means of depth selective Mössbauer spectroscopy, it was found that preliminary depositions of Ti films lead to the formation of α-Fe(Ti) solid solutions. Depending on the amount of deposited Ti, the α-Ti(Fe) solid solution and Fe?Ti intermetallic compounds can form. The influence of interfacial phases on the film adhesion is discussed.     

Competitive reactivity of iron towards boron and silicon in surface treatments with powder mixtures

The processes occurring at the surface of iron in contact with fluoride-activated B₄C-base powder mixtures at 850°C were investigated by substituting the diluent SiC with different silicon compounds. The coatings were analyzed by X-ray diffraction, surface Mössbauer spectroscopy and metallographic techniques. The possibility of passing from iron boriding to iron siliciding was shown, and a mechanism proposed for the process.     

Spin-order and magnetic properties of BaZn2Fe16O27 (Zn2-W) hexagonal ferrite

M?ssbauer and magnetic measurements have been carried out both on single crystals and polycrystalline samples of BaZn₂Fe₁₆O₂₇ (Zn₂-W) hexagonal ferrite. The saturation magnetization at 0 K and at room temperature turns out to be very high, that is, 123 and 79 Gauss·cm³/g, respectively. The results have been interpreted by assuming a local reversal or a weakening of the Fe³⁺ magnetic moments due to the perturbing action of Zn²⁺ ions. The magnetic anisotropy is confirmed to be uniaxial with an anisotropy field at room temperature of 12.500 Oe.     

Oxidation phenomena at the surface of iron alloys during laser treatments

An 1C-1.5Cr steel was laser treated under conditions suitable to obtain surface melting. The surface oxidizing phenomena and the laser-induced transformations were studied by means of surface Mössbauer measurements, X-ray diffraction and metallography. Significant modifications in the transformations, caused by surface oxidation, were correlated to the carbon availability at the surface during the treatments.     

Magnetic Anisotropy and the Appearance of Stripe Magnetic Domains in Co/Fe Multilayers

Thin Co/Fe multilayers were e-beam evaporated in ultra-high vacuum, keeping constant the Co layer thickness and varying that of Fe in the 0.5÷15 nm range. By increasing the Fe layer thickness, a component of magnetization perpendicular to the film plane rises up, and long and parallel magnetic domains (stripe domains) appear. The phenomenon is explained on the basis of the competition between the magnetoelastic anisotropy induced by stresses at the interfaces, and the shape anisotropy constraining the magnetization in the film plane. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic properties and spin order of Sr7Fe10O22

The magnetic properties of Sr₇Fe₁₀O₂₂ have been investigated by means of magnetic susceptibility and Mössbauer absorption measurements. This compound proved to be antiferromagnetic with a Néel temperature T_N = 425 K; the magnetic susceptibility is constant from the lowest measuring temperature (78 K) up to T_N.The Mössbauer measurements and the analogies with “brownmillerite” type compounds indicate that iron ions occupy one octahedral and two tetrahedral different sites. An antiferromagnetic spin configuration with moments lying in the ab plane appears to be consistent with the experimental results. A small spontaneous magnetic moment was observed at room temperature with features resembling those of strontium hexaferrite; a weak ferromagnetic behavior can not however be excluded taking into account the aforementioned susceptibility behaviour.     

High temperature solid state reactivity between iron and chromium monoborides

Powder mixtures of FeB and CrB were compacted and then treated at 1000 C under vacuum for 8 h in order to obtain information on the solid state reactivity of the monoborides, useful to clarify the growth mechanism of boride coatings on chromium steels and to optimize the conditions of the thermochemical process. The effects of diffusion phenomena are pointed out and the relevant mechanisms discussed.