Films superparamagnetism

Thirdly, the superparamagnetic state of the studied films is shifted to higher X (far beyond the percolation threshold) by addition of nitrogen into the vacuum chamber. 

The Mossbauer Fe spectra of the films represent the singlet with isomeric shift 5 = +0.20 mm/s and very weak splitting (Fig. 2). This can be probably due to relaxation processes in the nanosized Fe particles. The dimensions of the superparamagnetic iron particles can be estimated to be 30-50 nm. 

Ion irradiation of gel films prepared from mixtures of triethoxysilane with Fe and Ni nitrates permits to obtain a precipitation of metallic particles in a glassy matrix, because of the reduction ability of the hydrido group of the precursor for Fe and Ni ions. The metal particles, with a narrow range of sizes, exhibit a superparamagnetic behavior in a static field of low amplitude. However, their testing by electron spin resonance put into evidence a correlation of the spins parallel to the film surface. 

It was revealed that at deposition of the nanocomposite films in the Ar + O2 gas mixture the region of the superparamagnetic state was expanded far beyond percolation threshold %c determined from the electrical properties of the films deposited in pure Ar. An inductive contribution in equivalent circuits of the studied films shows that the currentconducting routes within the film bulk look like a system of nanocoils embedded in the alumina matrix. 

The as-prepared FePt nanopartides exhibited a chemically disordered fee structure, with relatively poor magnetic properties. Thus, fee FePt nanopartides were superparamagnetic at room temperature, and could be handled in the form of a colloidal solution for casting films, and produdng self-assembled arrays, for example (Figure 3.128). Further, the FePt nanopartides could be annealed at 550-600°C... 

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