Growth of nanosized MnAs/Si(111) magnetoelectronic heterostructures and their magnetooptical study

Thin (6–12 nm) epitaxial MnAs films were MBE-grown on Si(111) substrates under different technological conditions. The films feature essentially different surface morphology. This manifests itself in the formation, on the silicon surface, of hexagonal-shaped crystallites, whose dimensions vary depending on the growth conditions. The volume and surface magnetic properties of the films were studied using the magnetooptical Kerr effect and optical second harmonic generation. The Kerr effect was found to scale linearly with the effective thickness of the magnetic layer. The thickness of the magnetically disordered transition layer formed near the interface with the substrate was estimated. The surface and volume hysteresis properties of the films were found to be different. A contribution to the second-harmonic intensity was observed which is an odd function of magnetization. This effect originates from the interference of the magnetic and nonmagnetic contributions to the nonlinear polarization.     

Problems of Stability of Dynamical Systems and Computer Algebra

Examples of problems of motion stability solved with the help of computer algebra systems (CAS) are presented. The authors have experience in developing and applying problem-oriented systems of symbolic computations and software packages for solving problems of dynamics of multi-body systems. The algorithms under consideration are implemented (completely or partly) with the aid of up-to-date CAS. They are intended for inclusion in the ``Stability' package of symbolic computation. Bibliography: 6 titles.     

Longitudinal conductivity of thin films of La1 − x Sr x F3 − x solid solutions on glass ceramics

The longitudinal conductivity of La_{1 ? x} Sr _x F_{3 ? x} solid solution films (x = 0–0.24) with thicknesses of 40–260 nm grown on glass ceramics at temperatures from room temperature to 300°C and frequencies of 10^?1–10⁶ Hz was studied by impedance spectroscopy. The concentration dependence of film conductivity on the SrF₂ content had a maximum near x = 0.05. An equivalent circuit was constructed on the basis of the impedance plots to describe migration processes. The DC conductivity was evaluated for all samples under study. The activation energies were estimated from the temperature dependences of the DC conductivities of the films. The resulting dependences of electrophysical parameters were compared with those for bulk materials in terms of the relaxation conductivity model.     

Exciton luminescence in orthorhombic-structure MnF<Subscript>2</Subscript> epitaxial films

The low-temperature photoluminescence (PL) of 100 to 300-nm thick MnF₂ epitaxial films of the α-PbO₂-type orthorhombic structure was studied. The PL spectrum consists mainly of a broad band peaking around 575 nm and a slowly decaying long-wavelength wing. The short-wavelength part of the main band revealed relatively weak spectral features, which are due to magnon replicas of the Mn²⁺ excitonic line perturbed by Mg and Ca impurities. These features were found to shift toward shorter wavelengths by 12 nm relative to their position in bulk MnF₂ crystals. The shift can be accounted for by a change in the crystal field acting on the Mn²⁺ ions in the orthorhombic phase.     

Magneto-optical phenomena in MnAs/CaF2/Si(111) epitaxial films in a transverse magnetic field

Field and angular dependences of the rotation of the plane of polarization in a transverse magnetic field H⊥k under normal reflection of light (λ=633 nm) have been studied in MnAs ferromagnetic epitaxial films grown by MBE on CaF₂/Si(111) substrates. The angle of rotation of the plane of polarization a is shown to be determined by contributions even and odd in the magnetization M. The odd contribution is associated with the deviation of the easy plane of magnetic anisotropy from the film plane, which originates from misorientation of the Si surface from the (111) plane, or from a presence of small regions of ( )-oriented MnAs. The even contribution is due to the optical anisotropy of films connected with quadratic-in-M terms in the dielectric permittivity tensor ɛ _ij of manganese arsenide. A method based on measuring the angular dependences of a in a rotating magnetic field is proposed to separate these contributions. Fiz. Tverd. Tela (St. Petersburg) 41, 110–115 (January 1999)     

Generation of second optical harmonic and magnetooptical Kerr effect in ferromagnet-semiconductor heterostructures CaF2/MnAs/Si(111)

The second optical harmonic generation and magnetooptical Kerr effect are investigated for the light (λ=800 nm) reflected by ferromagnet-semiconductor heterostructures CaF₂/MnAs/Si(111). The observed change in the second-harmonic intensity is odd in magnetization. A phenomenological analysis of possible contributions to the second harmonic is carried out, and the sources of optically nonlinear signals are determined from the experimental azimuthal dependences of the light intensity at double frequency. The difference in the field dependences of the second harmonic and the magnetooptical Kerr effect is observed.