Developing of AC magnetometer and investigation of magnetic properties of LSMO

In this work AC magnetometer was developed and primary test measurements were performed for temperature range from 77 K up to 350 K in frequency range from 1 kHz up to 20 kHz. In the course of the present work dependencies of magnetization on temperature for Lao7Sr03Mni _yFeyO3 with y = 0.15, 0.20, 0.25 were obtained in DC magnetic field using SQUID magnetometer and in AC magnetic field using the developed AC magnetometer. Lai.XSrXMnO3 (LSMO) compounds belong to the class of Mn perovskites, which demonstrate very high degree of spin polarization. These materials are of great importance for nowadays applications in spintronics, where spin polarized electron transport is used. Spin glass like behavior was found as a characteristic feature of these solid solutions with the freezing temperature in the range 65 — 210 K.

Quantum transport phenomena and shallow impurity states in CdSb

This work is dedicated to investigation of the energy spectrum of one of the most anisotropic narrow-gap semiconductors, CdSb. At the beginning of the present studies even the model of its energy band structure was not clear. Measurements of galvanomagnetic effects in wide temperature range (1.6 - 300 K) and in magnetic fields up to 30 T were chosen for clarifying of the energy spectrum in the intentionally undoped CdSb single crystals and doped with shallow impurities (In, Ag). Detection of the Shubnikov - de Haas oscillations allowed estimating the fundamental energy spectrum parameters. The shapes of the Fermi surfaces of electrons (sphere) and holes (ellipsoid), the number of the equivalent extremums for valence band (2) and their positions in the Brillouin zone were determined for the first time in this work. Also anisotropy coefficients, components of the tensor of effective masses of carriers, effective masses of density of states, nonparabolicity of the conduction and valence bands, g-factor and its anisotropy for n- and p-CdSb were estimated for the first time during these studies. All the results obtained are compared with the cyclotron resonance data and the corresponding theoretical calculations for p-CdSb. This is basic information for the analyses of the complex transport properties of CdSb and for working out the energy spectrum model of the shallow energy levels of defects and impurities in this semiconductor. It was found out existence of different mechanisms of hopping conductivity in the presence of metal - insulator transition induced by magnetic field in n- and p-CdSb. Quite unusual feature opened in CdSb is that different types of hopping conductivity may take place in the same crystal depending on temperature, magnetic field or even orientation of crystal in magnetic field. Transport properties of undoped p-CdSb samples show that the anisotropy of the resistivity in weak and strong magnetic fields is determined completely by the anisotropy of the effective mass of the holes. Temperature and magnetic field dependence of the Hall coefficient and magnetoresistance is attributed to presence of two groups of holes with different concentrations and mobilities. The analysis demonstrates that below Tcr ~ 20 K and down to ~ 6 - 7 K the low-mobile carriers are itinerant holes with energy E2 ≈ 6 meV. The high-mobile carriers, at all temperatures T < Tcr, are holes activated thermally from a deeper acceptor band to itinerant states of a shallower acceptor band with energy E1 ≈ 3 meV. Analysis of temperature dependences of mobilities confirms the existence of the heavy-hole band or a non-equivalent maximum and two equivalent maxima of the light-hole valence band. Galvanomagnetic effects in n-CdSb reveal the existence of two groups of carriers. These are the electrons of a single minimum in isotropic conduction band and the itinerant electrons of the narrow impurity band, having at low temperatures the energies above the bottom of the conduction band. It is found that above this impurity band exists second impurity band of only localized states and the energy of both impurity bands depend on temperature so that they sink into the band gap when temperature is increased. The bands are splitted by the spin, and in strong magnetic fields the energy difference between them decreases and redistribution of the electrons between the two impurity bands takes place. Mobility of the conduction band carriers demonstrates that scattering in n-CdSb at low temperatures is strongly anisotropic. This is because of domination from scattering on the neutral impurity centers and increasing of the contribution to mobility from scattering by acoustic phonons when temperature increases. Metallic conductivity in zero or weak magnetic field is changed to activated conductivity with increasing of magnetic field. This exhibits a metal-insulator transition (MIT) induced by the magnetic field due to shift of the Fermi level from the interval of extended states to that of the localized states of the electron spectrum near the edge of the conduction band. The Mott variablerange hopping conductivity is observed in the low- and high-field intervals on the insulating side of the MIT. The results yield information about the density of states, the localization radius of the resonant impurity band with completely localized states and about the donor band. In high magnetic fields this band is separated from the conduction band and lies below the resonant impurity bands.

Spin-Dynamics in Cold Gases of 87Rb and Atomic Hydrogen. The spins they are a-changin’

In this thesis the dynamics of cold gaseous atoms is studied. Two different atomic species and two different experimental techniques have been used. In the first part of the thesis experiments with Bose-Einstein condensates of Rb-87 are presented. In these experiments the methods of laser cooling and magnetic trapping of atoms were utilized. An atom chip was used as the experimental technique for implementation of magnetic trapping. The atom chip is a small integrated instrument allowing accurate and detailed manipulation of the atoms. The experiments with Rb-87 probed the behaviour of a falling beam of atoms outcoupled from the Bose-Einstein condensate by electromagnetic field induced spin flips. In the experiments a correspondence between the phases of the outcoupling radio frequency field and the falling beam of atoms was found. In the second part of the thesis experiments of spin dynamics in cold atomic hydrogen gas are discussed. The experiments with atomic hydrogen are conducted in a cryostat using a dilution refrigerator as the cooling method. These experiments concentrated on explaining and quantifying modulations in the electron spin resonance spectra of doubly polarized atomic hydrogen. The modifications to the previous experimental setup are described and the observation of electron spin waves is presented. The observed spin wave modes were caused by the identical spin rotation effect. These modes have a strong dependence on the spatial profile of the polarizing magnetic field. We also demonstrated confinement of these modes in regions of strong magnetic field and manipulated their spatial distribution by changing the position of the field maximum.

Finland and the United States, 1917-1919 : early years of mutual relations

Doctoral dissertation, University of Helsinki

The Middle East in the American quest for world order : ideas of power, economics, and social development in United States foreign policy, 1953-1961

Doctoral dissertation, University of Tampere

Small-scale non-industrial private forest ownership in the United States : rationale and implications for forest management

Abstract

Spinor Bose-Einstein Condensates and Topological Defects

This thesis concentrates on the topological defects of spin-1 and spin-2 Bose-Einstein condensates, the ground states of spin-3 condensates, and the inert states of spinor condensates with arbitrary spin. Our work is based on the description of a spinor condensate of spin-S atoms in terms of a state vector of a spin-S particle. The results of the homotopy theory are used to study the existence and structure of the topological defects in spinor condensates. We construct examples of defects, study their energetics, and examine how their stability is affected by the presence of an external magnetic field. The ground states of spin-3 condensates are calculated using analytical and numerical means. Special emphasis is put on the ground states of a chromium condensate, whose dependence on the magnetic dipole-dipole interaction is studied. A simple geometrical method for the calculation of inert states of spinor condensates is presented. This method is used to find candidates for the ground states of spin-S condensates.

Scandinavian companies of banking, retailing and hotel sectors investing into the Baltic States-developing service sector

Diplomityö tehtiin Lappeenrannan yliopistossa päätavoitteenaan selvittää tärkeimmät motiivit, jotka ovat saaneet pohjoismaiset palvelualan yrityksetinvestoimaan Baltian maiden kehittyvillä markkinoilla. Pohjoismaiset yritykset ovat olleet aiemmin aktiivisia hyödyntämään Baltian maiden työvoimaa tuotantosektorilla. Suomalaiset yritykset ovat investoineet aiemmin telekommunikaatio- sekävaatetussektoreihin, mutta nykyisin investointien pääpaino on siirtynyt palvelualalle. Pankkisektori on erittäin kehittynyt pohjoismaissa ja ruotsalaiset yritykset ovat onnistuneet myös Baltiassa siirtyen markkinoille yksityistämisen tuomien mahdollisuuksien avulla. Nykyisin näillä yrityksillä on vahva jalansija Virossa sekä ovat etabloituneet myös Latviaan ja Liettuaan. Suomalaiset pankkialan yritykset ovat olleet vaatimattomampia tällä sektorilla. Vähittäiskauppiaat ovat vasta kansainvälistymisprosessinsa alkutaipaleella. Suomalaiset yritykset ovat laajentuneet Viroon ja tehneet yhteistyötä ruotsalaisten yritysten kanssa. Hotellisektorilla suomalaiset ja ruotsalaiset ovat edenneet rauhallisesti, mutta norjalainen ketju, Reval Hotel, on laajentunut kaikkiin Baltian maihin. Hotellisektorilla on luvassa kasvua lähivuosina. Kilpailutilanne on kiristynyt kaikilla palvelualan sektoreilla sekä paikallisten yritysten kasvun että ulkomaisten investoijien myötä. Elinolojen paraneminen vaikuttaa myös kilpailutilanteeseen kiristävästi, sillä se luo mahdollisuuksia yrityksille laajentua. Tämä diplomityö selvittäätilannetta valittujen yritysten kannalta niiden kansainvälistymisen alkutaipaleella.

European Union Eastern Enlargement - Expectations and Experiences of Doing Business in the New Member States

This publication deals with various aspects of European Union enlargement effects faced by the companies from EU15 and especially from Finland when doing business in the ten transitional economies which joined European Union in 2004 and 2007