Elena Gan’shina

Magnetorefractive Effect in Magnetoresistive Materials

In this chapter, we survey early and later experimental and theoretical results on the magnetorefractive effect in: (i) all-metal multilayers and granular alloys with giant magnetoresistance, (ii) metal–insulator multilayers and nanocomposites with tunnel magnetoresistance, (iii) bulk single- and polycrystals, thin films and heterostructures of manganites with colossal magnetoresistance, focusing on recent developments that have led to a better understanding of the magnetorefractive effect in the infrared and visible range of spectrum and to the recognition of unsolved problems and possible routes for the magnetorefractive effect enhancement. The possible applications of the magnetorefractive effect are also discussed.

The Influence of Si on Magnetic and Magneto-Optical Properties of Co/Si/Co Thin-Film Systems

The magnetic and magneto-optical properties of the Co/Si/Co thin-film samples obtained by magnetron sputtering were investigated employing magnetooptical techniques. The thickness of the Co layers was equal to 5 nm, and Si layer thickness varied in the interval of 0.2 to 3.2 nm. The magnetic saturation field of the samples under study was found to oscillate in the magnitude with the change of the Si layer thickness. This result was explained by structural features of the Co/Si/Co multilayers and the presence of the antiferromagnetic exchange coupling between magnetic layers via the silicon interlayer. The peculiarities of the magneto-optical spectra of the Co/Si/Co samples were measured and discussed.

Magnetic and Magneto-Optical Research of Ni43.7Mn43.6In12.7 Ribbons

We report the magnetic and magneto-optical (MO) properties of the Heusler Ni43.7Mn43.6In12.7 alloy ribbon in martensitic and austenitic states. The samples were produced by rapid solidification using the melt-spinning technique. The difference between the transformation temperatures obtained from magnetization and transverse Kerr effect (TKE) measurements shows that the chemical composition and/or microstructure are not identical in the bulk and at the ribbon surface. The TKE spectra profile in the spectral energy range of 0.5-3.5 eV does not change significantly at the martensitic transformation that indicates on a very similar electronic structure in martensitic and austenitic states.

Magneto-Optical Study of Martensitic Transition in Ni45Mn36.7In13.3Co5 (at. %) Single Crystals

Transverse Kerr effect (TKE) was used to study magneto-optical (MO) properties of Ni45Mn36.7In13.3Co5 (at.%) single crystals. A single crystalline ingot of such composition was grown by the Czochralski method. One series of samples was quenched into cold water (WQ) and the other series after quenching was heated at 770 K for 20 min and slowly cooled to assure a complete atomic order (SC). Accordingly to differential scanning calorimetry (DSC), magnetic and magneto-optical (MO) measurements, WQ samples exhibit well-defined martensitic transition (MT), but the SC samples do not show MT. It is found that TKE for WQ samples shows the following features (i) MO signal is well pronounced far below the martensitic transition in spite of a weak magnetization of martensitic phase; (ii) the characteristic temperatures of martensitic transition differ from those for the bulk and depend on annealing conditions; (iii) MO spectra profile do not change significantly during the martensitic transition and is similar but not identical with that for Ni50Mn35In15 thin films and Ni43.7Mn43.6In12.7 ribbons measured before; (iv) MO signal is anisotropic.

Transversal Kerr Effect of In1-xMnxAs layers prepared by ion implantation followed by pulsed laser annealing.

In1− x Mn x As (x = 6.9%) layers prepared by ion implantation and subsequent pulsed laser annealing have been studied using the magnetooptical transversal Kerr effect (TKE) and spectral ellipsometry. Ellipsometry data reveal the good crystal quality of the layers. The samples show ferromagnetic behaviour below 77 K. Near the absorption edge of the parent InAs semiconductor, large TKE values are observed. In the energy regions of the transitions in the Γ and L critical points of the InAs Brillouin zone, there are several clearly defined structures in the low-temperature TKE spectra. We have calculated the spectral dependences of the diagonal and nondiagonal components of the permittivity tensor (PT), as well as the spectrum of magnetic circular dichroism (MCD) for our samples. A number of extrema in the obtained MCD and PT spectra are close to the energies of transitions in the critical points of the parent semiconductor band structure, which confirms the intrinsic ferromagnetism of the Mn-doped InAs layers.

Magneto-Optical Properties of Multilayer Nanostructures with Composite Magnetic Layers near Percolation Threshold

Spectra and field dependencies of Transversal Kerr Effect (TKE) for [(Co45Fe45Zr10)46(Al2O3)54(X)/Si (Y)]n multilayers (ML) with thin layers (X < 2,5 nm; Y < 3,5 nm) have been studied in the energy range 0,5 – 4,0 eV. It was found that TKE field dependencies in the nearest infrared (IR) and visible energy ranges exhibit anomalous behavior. TKE spectra measured in weak (~30 Oe) and strong (~2 kOe) magnetic fields were essentially different. It was shown that magneto-optical response of multilayered structure composite-silicone is the sum of magnetic composite layers and composites formed on interface contributions. And these contributions may have an opposite sign of TKE. Interface magnetic states depend on composite and semiconductor layers’ thicknesses and FM phase concentration in composite layers.

Magneto-Optical Evidence for Intrinsic Ferromagnetism in (Ga,Mn)As Layers Grown by Pulsed Laser Deposition

GaMnAs layers fabricated on GaAs(001) substrates by laser ablation technique were studied using the magneto-optical transversal Kerr effect (TKE) (E = 0.5 - 4.0 eV) and spectral ellipsometry (E = 1.4 - 4.5 eV). Obtained spectral, temperature and magnetic field TKE dependences shown that the used technique allowed us to obtain ferromagnetic (Ga,Mn)As layers, whose composition was close to single-phase one (without MnAs inclusions). Spectral dependences of the off-diagonal components (e’ = e’1 - ie’2) of the permittivity tensor and also of the magnetic circular dichroism (MCD) were calculated for ferromagnetic (Ga,Mn)As sample. The calculated dependences were compared with the published magneto-optical spectra of (Ga,Mn)As layers grown by molecular beam epitaxy.

Magnetic, magnetooptical, and magnetotransport properties of Ti-substituted Co2FeGa thin films

Magnetic, magnetooptical and magnetotransport properties of Co50.3Fe20.3Ti5.6Ga23.8 thin films were studied for the as prepared as well as annealed samples. Measurements of transverse magnetooptical Kerr effect revealed that the spectral response of the films strongly depends on the structural ordering which can be manipulated by annealing conditions. Peculiarities in the magnetic properties of the films were attributed to the coexisting phases with different degree of structural disorder. Magnetoresistance of Co50.3Fe20.3Ti5.6Ga23.8 thin films was found to be linear in the fields above 1 T which is typical for half-Heusler systems as well as for Heusler-based ferromagnetic shape memory alloys.

Magnetooptical Properties of Hg1-xCdxCr2Se4 Solid Solutions

Influence of the substitution of Hg by Cd on Kerr effect, magnetoreflection, and magnetotransmission of unpolarized light for Hg1-xCdxCr2Se4 (0≤x≤1) single-crystals is studied. The changes in the magnetooptical properties of the ferromagnetic spinels are shown to occur in compositions with x>0.1. The giant values of magnetooptical effects in Hg1-xCdxCr2Se4 spinels can be used in the magnetooptoelectronics.

Magnetorefractive Effect in Doped La1-xKxMnO3 Thin Films

Influence the deposition of La3+ ions by monovalent K+ ions on magnetorefractive effect on magnetoreflaction and magnetotransmission modes in the infrared range for La1-xKxMnO3 epitaxial thin-films (х=0.05, 0.10, 0.15 и 0.18) has been studied. It has been shown that the magnetorefractive effect, transversal Kerr effect and magnetoresistance reach the maximum in optimally doped films at highest Curie temperature. The good agreement between calculated in framework of magnetorefractive effect theory and experimental data takes place only for optimally doped films, with potassium concentrations of 15 % and 18 %. At the other doping levels the films become charge and magnetic inhomogeneous. Magnetic and charge homogeneity influence strongly on magnetooptical effects in films. The resonance-like lines in magnetoreflection spectra of films are connected with the shifting of reflection minimum before the phonon bands under a magnetic field has been observed.