Surface and bulk analysis of Sr2FeMoO6 thin films – Sr2FeMoO6 based spin valve

This thesis deals with the analysis of Sr2FeMoO6 (hereafter refered to as SFMO) thin films. The material is a part of a versatile double perovskite structure family and exhibits potential attributes for basic scientific interest and for spintronic application research. The introduction begins by outlining some of the features of SFMO as a material. The basic physics relevant for this work is also discussed. The experimental work has been mostly carried out in the Wihuri Physical Laboratory and is largely build around the fabrication and the characterization of SFMO thin films. All the SFMO thin film samples have been deposited using a pulsed laser deposition equipment. The characterization includes a surface sensitive atomic and magnetic force microscopy along with a scanning tunneling microscopy technique. The surface sensitive spectroscopy analysis for electronic structure is done using x-ray photoelectron spectroscopy. In addition, the structural characterization includes a bulk sensitive x-ray diffraction technique and magnetometry measurements. Based on the conducted work for the structural, magnetic and electronic characterization on the SFMO films, the effects of the deposition parameters are reported. The results demonstrate the influence of substrate materials, setting a possible threshold thickness for the films to overcome the interface defects and altering the orientation of the magnetization easy axis. The atomic force microscopy method showed an improvement in thin film surface structure, as lower surface roughness, with 900 _C deposition temperature compared with higher deposition temperatures. The surface structure of the SFMO films showed evidences of a single unit cell layer growth combined with island like growth. The electronic characterization revealed that the surface contamination in the SFMO films can be cleansed with ex-situ post-annealing. The annealing leads to significant valence fluctuation without any obvious unwanted side effects on SFMO. As a finishing touch to this work, the recent advancement in spin valve deposition is reported. The results demonstrate, to our knowledge, the first spin valve effect in SFMO thin film based devices with an organic semiconductor transport layer. The results show a notable spin valve effect at low temperature. Magnetoresistance shows a clear decay with increasing temperature, but the magnetoresistance response close to room temperature is still observed

Erikoisnäppäimistö painissa käytettävään tuloslaskentaohjelmaan

Opinnäytetyön tarkoituksena oli suunnitella ja valmistaa erikoisnäppäimistö painissa käytettävää tuloslaskentaohjelmaa varten. Näppäimistön tarkoitus on helpottaa ja nopeuttaa pisteiden syöttämistä tuloslaskentaohjelmaan sekä estää pisteiden syöttövaiheessa tapahtuvia virheitä. Erikoisnäppäimistö on toteutettu käyttämällä normaalia näppäimistömikrokontrolleria. Tästä syystä ei ole tarvinnut tehdä mitään ohjelmointityötä, koska mikrokontrolleri pitää sisällään kaikki näppäimistön ja tietokoneen väliseen kommunikointiin tarvittavat ohjelmistorutiinit. Näppäimistö on pyritty tekemään käyttäjäystävälliseksi ja mahdollisimman helpoksi käyttää. Näppäimistön painonapit on ryhmitelty loogisesti siten, ettei käyttäjän tarvitse etsiä oikeita näppäimiä, ja käyttäjä voi keskittyä seuraamaan painiottelun kulkua. Painikilpailuissa näppäimistöä käyttää ylituomari tai erityisesti ottelupisteiden syöttötehtävään määrätty ja opastettu henkilö.The purpose of this thesis was to design and manufacture a special keyboard for wrestling score software. The purpose of the special keyboard is to ease and speed up giving points and to prevent errors in entering the points, during wrestling match. In the special keyboard a standard keyboard microcontroller was used. Therefore, it was not necessary to make of any kind a programming work, because the microcontroller already included all software routines between a keyboard and computer communications. The design of the special keyboard aimed to be user-friendly. The push buttons of the special keyboard have logically arrangement, so the users do not need look for the correct buttons and they can focus on following the wrestling match. The special keyboard will be used in the wrestling matches by the mat chairman or a trained perso

"Utmanande men intressant" -Studenternas åsikter om tvåspråkig utbildning vid Vasa universitet i ljuset av språkvärdering

Tutkimukseni tavoitteena on ollut selvittää korkeakouluopiskelijoiden näkemyksiä kielitaidosta ja kieliopinnoista koulutuksen aikana ja sen jälkeisessä työelämässä. Tutkimukseni kohteena ovat kaksikielisen koulutuksen mahdollisuudet ja haasteet. Tutkimus kartoittaa Vaasan yliopiston opiskelijoiden kielitaitoa ja kieliopintojen määrää, heidän kiinnostustaan kieliopintoja ja erityisesti kaksikielistä (suomi-ruotsi) koulutusta kohtaan. Kaksikielistä koulutusta tarkastellaan sekä arvostuksen että parhaan toteuttamistavan kannalta. Tutkimuksen tavoitteena on tuottaa tietoa, jonka pohjalta Vaasan yliopiston koulutusta voidaan kehittää mahdollisen kaksikielisen koulutuksen suuntaan. Tutkimus kuuluu tutkimusryhmä BilingCon vuonna 2010 käynnistämään hankkeeseen Kaksikielisyys ja monikulttuurinen Suomi - hyviä käytänteitä ja tulevaisuuden haasteita (Kamoon). Kamoon-hankkeen tavoitteena on selvittää, minkälaiset vuorovaikutukset toimintakulttuurit ja -mallit tukevat parhaiten organisaatioiden kaksikielisyyttä suomalaisessa yhteiskunnassa. Tutkimukseni osoittaa, että opiskelijat pitävät kaksikielistä koulutusta aluesidonnaisena kilpailuvalttina rekrytointitilanteessa. Vaasan yliopiston kannalta kaksikielinen koulutus nähdään tulevaisuuden yhteistyömahdollisuutena sekä vahvuutena, joka mahdollisesti lisää kiinnostusta Vaasan yliopistoa kohtaan. Kaksikielisen koulutuksen mielekäs toteutus sekä koulutuksesta tiedottaminen nousi tutkimuksessa esiin tärkeänä tekijänä. Opiskelijoista 70 % oli sitä mieltä, että kaksikielisen koulutuksen toteuttaminen edellyttää kielenopettajan tukea. Tutkimuksen perusteella paras tapa toteuttaa kaksikielistä koulutusta ovat yksittäiset kurssit, kaksikielinen kurssimateriaali, eri korkeakoulujen opettajayhteistyö sekä ruotsinkielisten yksiköiden kurssien integrointi Vaasan yliopiston kursseihin.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Refined Sr2FeMoO6 interface realized with photoemission and magnetization analysis

We investigate the effects of post-annealing on a set of identically deposited Sr2FeMoO6 (SFMO) thin films. The annealing provides a significant enhancement to ferrimagnetic exchange, evidenced by almost 40 K increase in Curie temperature. The electronic nature of the film surface is our focus of interest. The detailed analysis on oxygen 1s, strontium 3d, molybdenum 3d spectrum along with changes in the carbon contamination show purification from additional phases and significant valence fluctuation. Successful treatment provides films with higher Curie temperature and diminished surface contamination. Annealing therefore provides a possible method of reobtaining a portion of the valuable bulk attributes at interfaces in e.g. spin valve structures.</p

Increased Curie temperature and magnetoresistive response by modifying Fe/Mo ratio in Sr2FeMoO6 thin films

We investigated the effect of deposition distance on a set of otherwise identically grown Sr2FeMoO6 (SFMO) thin films grown by pulsed laser deposition. Based on the detailed magnetic and transport measurements, we found that the optimal properties can be realized at longer deposition distances than earlier expected. The achieved onset Curie temperature of the order of 400 K with the middle transition value of 372 K, which are clearly the highest presented in the literature for the SFMO thin films. In addition, the increased metallicity and magnetoresistive response is observed in films deposited at longer distances. The improvements are widely discussed in the light of discovered stoichiometric imbalance between the cations Fe and Mo, which modify the magnetic interactions and thus magnetic and electric properties. Therefore, this study shows a new approach in the deposition process to provide the SFMO thin films and multilayers of high quality for future spin valve devices working at room temperature.</p

Giant magnetoresistance response in Sr2FeMoO6 based organic spin valves

We report the fabrication of the first Sr2FeMoO6 based organic spin valve device using Tris(8-hydroxyquinolinato) aluminum (Alq(3)) as a spin transport layer. The characterization of the device confirms hysteretic magnetoresistance with approximately 20%-30% switching between high and low resistance states at low temperatures. The results demonstrate that organic semiconductors can form a suitable interface with double perovskite, half metallic Sr2FeMoO6, for efficient low temperature operation and have a potential to improve the room temperature performance significantly in tunneling devices where decay in spin diffusion length of organic layer does not affect the transport

One-Pot Transformation of Citronellal to Menthol Over H-Beta Zeolite Supported Ni Catalyst: Effect of Catalyst Support Acidity and Ni Loading

Citronellal was converted to menthol in a one-pot approach using H-Beta zeolite-based Ni catalyst in a batch reactor at 80&nbsp;°C, under 20&nbsp;bar of total pressure. The effects of H-Beta acidity (H-Beta-25 with the molar ratio SiO2/Al2O3 = 25 and H-Beta-300 with SiO2/Al2O3 = 300) and Ni loading (5, 10 and 15&nbsp;wt %) on the catalytic performance were investigated. Ni was impregnated on H-Beta support using the evaporation-impregnation method. The physico-chemical properties of the catalysts were characterized by XRD, SEM, TEM, ICP-OES, N2 physisorption, TPR, and pyridine adsorption–desorption FTIR techniques. Activity and selectivity of catalysts were strongly affected by the Brønsted and Lewis acid sites concentration and strength, Ni loading, its particle size and dispersion. A synergetic effect of appropriate acidity and suitable Ni loading in 15&nbsp;wt.% Ni/H-Beta-25 catalyst led to the best performance giving 36% yield of menthols and 77% stereoselectivity to (±)-menthol isomer at 93% citronellal conversion. Moreover, the catalyst was successfully regenerated and reused giving similar activity, selectivity and stereoselectivity to the desired (±)-menthol isomer as the fresh one. Graphical Abstract: [Figure not available: see fulltext.

Electrocatalytic hydrogenation of glucose and xylose using carbon fiber supported Au nanocatalysts

Recent evidences have shown catalyst structure sensitivity of electrocatalytic hydrogenation (ECH) of organic molecules in aqueous phase. In this study, ECH of glucose and xylose was investigated using gold nanoparticles (AuNPs) on activated carbon fiber (CF) support as catalyst. CF supported AuNPs catalysts (CF/AuNPs) were synthesized by deposition-precipitation method and were characterized by physicochemical (SEM, TEM, XRD, N2 physisorption, ICP-OES) and electrochemical methods. Chemical or thermal pre-treatment of CF prior to Au deposition resulted in different AuNPs size distributions. The activity towards glucose or xylose ECH were observed to be dependent on the particle size of AuNPs and the applied potential. Compared to a polycrystalline Au catalyst, higher reaction rates for glucose and xylose ECH were observed for a CF/AuNPs catalyst with a higher surface area. This indicates that the activity of Au towards glucose and xylose ECH is dependent on the surface area and particle size, and particle size control can be achieved by simple chemical or thermal pretreatment of the catalyst support.</p

Exploring the anti-site disorder and oxygen vacancies in Sr2FeMoO6 thin films

AbstractTo address the importance of nanoscale defects in complex magnetic oxides, we present an effective tool, variable energy positron annihilation spectroscopy, for probing the relatively small changes in anti-site disorder and oxygen vacancies of the in situ annealed double perovskite SrFeMoO thin films. By controlling the annealing conditions in wide pressure and temperature ranges and thus affecting the amount of nanoscale defects, we show that the magnetic properties of SrFeMoO thin films can be modified, particularly with the oxygen nonstoichiometry, and hence their spintronic functionality can be improved. On the basis of our findings together with proposed mechanism, we suggest that the annealing treatments can also be scaled to other complex magnetic perovskites to engineer nanoscale defects and thus improve their usability in future spintronic applications.</p

Catalytic conversion of glucose to methyl levulinate over metal-modified Beta zeolites

Methyl levulinate was selectively formed from glucose and methanol over a copper modified Beta zeolite bifunctional catalyst at 180 degrees C under argon atmosphere. The selectivity to methyl levulinate substantially exceeded previously reported in the open literature results. The copper modification was done through an ion-exchange method using a solution of copper nitrate, followed by drying and calcination of the catalyst. Copper modification changed the distribution of acid sites namely, less Bronsted and more Lewis sites were observed with FTIR using pyridine adsorption. Application of the proton form H-Beta-25 gave the methyl levulinate yield of ca. 89%, which could be elevated with the addition of copper, as the apparent selectivity exceeds 99%, assuming that methyl glucosides are eventually transformed to methyl levulinate. The non-acidic Cu/SiO2 catalyst was completely inactive in methyl levulinate formation. Metal modification of Beta zeolite with Sn and Zn did not perform as well as Cu in the formation of methyl levulinate during glucose transformation