Magnetism and Magnetic Materials

Biography

Biography: Fedor Pudonin

Abstract

Now there has been a significant interest in the technology of obtaining and studying magnetic nanoisland films. This is due both to the enormous applied potential of these objects. We used the RF-sputtering method to obtain nanoisland films of magnetic materials such as FeNi, Co, Ni, etc. In this report we will present the results of our work on obtaining magnetic nanoisland films and some applied aspects of these structures. Since the deposition rate is a stable value at constant technological parameters, we deposit thin films whose effective thickness was determined by the time of deposition. There is a critical thickness d*(percolation threshold) below which the films are nanoisland, and films with effective thickness d>d* become continuous. To determine the d* value, we have grown several series of FeNi films with effective thicknesses from 0.5 to 3.0 nm with thickness steps Δ~0.07 nm. The standard polished ceramic plates (sitall), crystalline silicon, silicon nitride, glass, as well as thin Al₂O₃ layers deposited on silicon were used as substrates. Figure 1 shows an image of some island FeNi films. To determine d*, the dependences of the permittivity e(w) and conductivity s on the thickness were studied. It was found that Re e(w) and δ=[σ (T=300 K) - σ(T=77 K) simultaneously change sign at d~1.6-1.8 nm, which indicates the presence of a percolation transition at d*~1.6-1.8 nm. Thus, FeNi films with an effective thickness d<1.6 nm are island. We have shown that photoconductivity in the range 500-1500 nm, anomalous conductivity in weak electric fields, giant dielectric constant, and other unusual properties are observed in nanoisland films of FeNi and other metals. We proposed to use nanoisland FeNi films in which the effect of anomalous conductivity is observed as labels that can serve as a protection for various documents and securities and other products. Nanoisland films can also be used to create sensors of superweak magnetic fields at room temperature. For this, we fabricated multilayer island structures such as [FeNi/Co]_N in figure 2. With the help of X-ray studies it was shown that in such systems the island layers do not mix and they really are periodic structures. It was found that these structures are capable of detecting (changing their resistance) magnetic fields H<10^-11 T. This is a great result and we hope to improve it.