Magnetooptical, optical, and magnetotransport properties of Co/Cu superlattices with ultrathin cobalt layers

• Published in: Physics of the solid state 2017, Vol.59 (1), p.53-62
• Main Authors: Lobov, I. D., Kirillova, M. M., Makhnev, A. A., Romashev, L. N., Korolev, A. V., Milyaev, M. A., Proglyado, V. V., Bannikova, N. S., Ustinov, V. V.
• Format: Article
• Language: English
• Subjects: Cobalt; Ellipsometry; Energy spectra; Ferromagnetism; Kerr effects; Low temperature; Magnetic properties; Magnetism; Magnetoresistance; Magnetoresistivity; Magnetron sputtering; Optical properties; Physics; Physics and Astronomy; Solid State Physics; Superlattices; Tensors; Thickness; Transport properties
• ISSN: 1063-7834; 1090-6460
• DOI: 10.1134/S1063783417010206

We investigated the field dependences of the magnetization and magnetoresistance of superlattices [Co( t x , Å)/Cu(9.6 Å)]30 prepared by magnetron sputtering, differing in the thickness of cobalt layers (0.3 Å ≤ t Co ≤ 15 Å). The optical and magnetooptical properties of these objects were studied by ellipsometry in the spectral region of h ω= 0.09–6.2 eV and with the help of the transverse Kerr effect ( h ω= 0.5–6.2 eV). In the curves of an off-diagonal component of the tensor of the optical conductivity of superlattices with t Co = 3–15 Å, a structure of oscillatory type (“loop”) was detected in the ultraviolet region, resulting from the exchange splitting of the 3d band in the energy spectrum of the face-centered cubic structure of cobalt ( fcc Co). Based on magnetic experiments and measurements of the transverse Kerr effect, we found the presence of a superparamagnetic phase in Co/Cu superlattices with a thickness of the cobalt layers of 3 and 2 Å. The transition from superlattices with solid ferromagnetic layers to superparamagnetic cluster-layered nanostructures and further to the structures based on Co and Cu ( t Co = 0.3–1 Å) with a Kondo-like characteristics of the electrical resistivity at low temperatures is analyzed.