L'intérêt pour les multiferroïques réside dans la possibilité d'asservir les propriétés électriques du matériau à partir du magnétisme et vice et versa. Le champ d'application pour ce type de composé est vaste, mais les attentes sont particulièrement grandes pour le domaine de l'emmagasinage d'information, celui de la spintronique et pour l'innovation de nouveaux senseurs magnétiques. Les propriétés magnétoélectriques se manifestant à partir de différents phénomènes physiques sont encore aujourd'hui mal comprises et cela est particulièrement le cas pour le couplage existant entre les ordres magnétiques et la ferroélectricité des manganites de structure hexagonale. Cette thèse présente donc une étude optique de cette famille de manganite ayant pour but de lever le voile sur le mécanisme responsable de ses propriétés magnétoélectriques. Cette thèse présente une étude détaillée du comportement de l'énergie en température des modes de vibration Raman de plusieurs manganites hexagonales à base des terres rares : Y[indice supérieur 3+], Ho[indice supérieur 3+], Er[indice supérieur 3+] et Lu[indice supérieur 3+]. Leurs similarités ainsi que leurs différences en terme de phases magnétiques, de températures de transition et de déplacements atomiques permettront de mettre en évidence les interactions d'échange magnétique des ions de manganèse et de terre rare impliqués dans les phénomènes magnétoélectriques de ces composés. Il sera aussi démontré que ces interactions sont modulables par l'application d'un champ magnétique pour donner lieu à des transferts partiels de charges, calculés à partir des changements énergétiques des modes infrarouges, permettant la réplique exacte du comportement magnétoélectrique de la polarisation du HoMnO[indice inférieur 3]. Des mesures de transmission optique et de luminescence des niveaux électroniques 4[florin] du HoMnO[indice inférieur 3] seront aussi présentées. Il sera vu que des changements importants de plusieurs transitions électroniques en fonction de la température et du champ magnétique appliqué se produisent et se corrèlent aux transitions de phases magnétoélectriques du cristal. La modulation des intensités de certaines transitions électroniques, voire même leur apparition et leur disparition, indiquent que des changements importants dans l'hybridation des électrons 4[florin] du Ho[indice supérieur 3+] produisent avec les niveaux 3d du Mn[indice supérieur 3+], de parité opposée, affectant les règles de sélection optiques. Ceci confirme du même coup un rôle majeur de ces derniers dans les phénomènes magnétoélectriques. Cette idée sera renforcée avec l'observation de transitions vibroniques indiquant une forte interaction des électrons 4[florin] du Ho[indice supérieur 3+] avec les modes de vibration du cristal qui ne peuvent se produire que via des effets d'hybridation étant donné leur confinement spatial et électronique.

Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: In this investigation the formation of thin film manganites and their electrical characteristics is studied. In order to see the effect of oxidation states on magneto-resistivity, 80% of Mn is replaced by Fe. Pulsed laser deposition (3 J/cm2), carried out in oxygen partial pressures ranging from 0.01 mbar to 1.00 mbar was used to fabricate the thin films from two target compositions, namely La2CaMn2.94Feo.0609 and La2CaMno.6Fe2.409. Films were deposited on Si< 100 >, MgO< 100 >, SrTi03< 100 > and LaAl03< 100 > single crystal substrates. Samples were characterized by RBS, AFM, SEM, and XRD. Electrical measurements were also carried out. One of the main characterization techniques in this investigation is Rutherford Backscattering Spectrometry (RBS). It has been shown that RBS is a very powerful characterization technique when used in conjunction with the RUMP simulation program. The effect of various parameters can be determined beforehand by RUMP simulation of the thin film structures to be investigated. Simulation shows that RBS is an excellent characterization tool for determining film thickness and stoichiometry. The role of oxygen uptake in La2CaMn3_xFexOg was investigated as the oxidation states of elements in manganite materials have a large effect on their magnetoresistive properties. The height of the La signal can be used as a measure of the oxygen content. RBS spectra of films deposited on single crystal silicon substrates at different ambient pressures show that the fit between simulated and measured RBS spectra improves with higher oxygen pressures, thereby indicating better quality manganite material. The RBS spectra also show that the films have good stoichiometry. Atomic force microscopy was used to determine the roughness of the thin films. The annealed film (average roughness 4.5 nm) shows a surface smoother than the non-annealed film (average roughness 5.3 nm). SEM measurements show that in the case of samples having a high Fe content, the crystallite size varies between about 0.04 11m and 0.10 11m, while for samples with high manganese content, the crystallinity varies between 0.03 jJ,m and 0.06jLm. Manganites were analyzed using Bragg-Brentano (28) X-ray diffraction. Measurements show that manganite films cannot be grown epitaxially on Si< 100 > and MgO< 100 > single crystals due to a large lattice mismatch. In the case of SrTi03 and LaAl03 several reflections and sharp peaks from the film can be seen, indicating reasonable epitaxial growth. SEM measurements of the samples however show polycrystallinity. Complete epitaxy has thus not occurred, but many grains have an epitaxial orientation. Resistance versus temperature (the room temperature to about 100 K) in zero magnetic field was measured for a La2CaMno.06Fe2.409 thin film and maximum resistance corresponding to about 108 K was found. At higher temperatures the resistance decreases as temperature increases. The manganite thin film therefore shows semiconductor behaviour. Resistance measurements carried out at different magnetic fields (0 - 1 T) show a small positive magnetoresistance of 0.83 %. Usually the magnetoresistance phenomenon is measured at higher magnetic fields and this could be the reason for our low value as well as the fact that the iron content could be too high. / AFRIKAANSE OPSOMMING: In hierdie ondersoek is die formasie en karakterisering van dunlagie manganiete ondersoek. Om die effek van oksidasie-toestand op magnetoresistiwiteit te bepaal, is 80% van die Mn verplaas deur Fe. Pulseerde laser deposissie(3 J/cm2), is uitgevoer by 'n parsiële suurstof druk tussen 0.10 en 1.00 mbar deur gebruik te maak van La2Ca Mn2.94Feo.o609 en La2CaMno.6Fe2.409 teiken skywe. Dunlagies was gedeponeer op Si<IOO>, MgO<IOO>, SrTi03<100> en LaAl03<100> enkelkristal substrate. Die dunlagies is daarna ge-karakteriseer met behulp van Rutherford terugverstrooing (RBS), atoom krag mikroskopie(AFM), skandeer elektronmikroskopie (SEM) en xstraal diffraksie(XRD). Elektriese metings is ook uitgevoer. Een van die hoof tegnieke wat gebruik is in hierdie ondersoek is Rutherford terugverstrooing (RBS) van 2 Mev alfa-deeltjies. In hierdie navorsing is aangetoon dat RBS saam met spektra simulasie(RUMP), 'n besondere kragtige metode is om die stoichiometrie en dikte van manganiet lagies te bepaal. Die rol van die opname van suurstof in die dunlagies was ondersoek, aangesien die oksidasie toestand van manganiet lagies 'n groot effek het op hulle magnetoresistiwiteit. Die hoogte van die La sein is gebruik as 'n maatstaf van suurstof inhoud. RBS spektra van dunlagies gevorm op enkelkristal silikon substrate by verskillende parsiële suurstof drukke wys dat die passing tussen gemete en gesimuleerde spektra verbeter by hoër suurstof drukke, wat beter kwaliteit manganiet materiaal aandui. Die RBS spektra het ook aangetoon dat die stoichiometrie van die lagies uitstekend is. Atoom krag mikroskopie(AFM) is gebruik om die grofheid van die oppervlaktes van die dunlagies te bepaal. Lagies wat by 750 grade celsius uitgegloei is ( gemiddelde gladheid van 4.5 nm) was gladder as films wat nie na ablasie uitgegloei is nie (gemiddelde gladheid van 5.3 nm). SEM metings toon ook dat dunlagies met 'n hoë Fe inhoud 'n kristalliet deursnit het van 0.04 tot 0.10 mikrometer en die met 'n hoë mangaan inhoud 'n poli-kristalliniteit het van tussen 0.03 en 0.06 mikrometer het. Bragg-Brentano(twee-theta) X-straal diffraksie meting wys dat manganiet films nie epitaksieël op Si<IOO> en MgO<IOO> enkelkristal substrate gevorm kan word nie, weens 'n groot verskil in die kristal-rooster parameters. SEM metings van die monsters wys polikristalliniteit. Algehele epitaksie het dus nie plaasgevind nie, maar verskeie kristalliete het 'n epitaksiële orientasie. Weerstand metings is gemaak by temperature so laag as 100 Kelvin vir La2CaMno.o6Fe2.409dunlagies en 'n maksimum weerstand is by 108 Kelvin gevind. By hoër temperature het die weerstand afgeneem soos die temperatuur toeneem, wat halfgeleier gedrag aandui. Weerstand metings by verskillende magneetvelde (0 tot I Tesla) wys 'n klein magnetoresistiwiteits effek van 0.83%. Gewoonlik word magnetoresistiwiteit gemeet by hoë magneet velde (ongeveer 6 Tesla). Dit, sowel as die hoë Fe samestelling van die monsters kan die rede wees vir die lae magnetoresistiwiteit wat waargeneem word.

This thesis presents three investigations of the magnetic and electronic proper- ties of manganese oxide materials. The investigations are performed using a variety of neutron scattering and x-ray scattering techniques. The electronic ground-state of Pr(Sr_0.1 Ca_0.9)₂ Mn₂O₇ an antiferromagnet with CE-type ordering, is determined using neutron spectroscopy, as opposed to the more usual approach of using diffraction. The Zener polaron model of the elec- tronic ground state of the CE-type magnetic phase is shown to be unsuitable for this material. The ground-state is shown to agree well with the electronic ground state proposed by Goodenough in the 1950’s, but without significant Mn^3&plus;/Mn^4&plus; disproportionation. The distribution of the magnetisation density within the unit cell of the CE-type antiferromagnet La_0.5Sr_1.5MnO₄ is determined from a polarised neutron diffraction experiment by analysing the results with the maximum entropy method. The majority of the magnetisation density is found to be located at the Mn site. The investigation shows tentative evidence of a small magnetic moment on the in-plane O site. However, a larger moment is observed at both the La/Sr site and the out-of-plane O site. The magnetic structure of the magnetoelectric multiferroic DyMn₂O₅ is inves- tigated using resonant magnetic x-ray scattering. The magnetic structure is shown to be similar to other members of the RMn₂O₅ series of multiferroics, but with the key difference that the magnetic moments are closely aligned parallel with the crystallographic b-axis, in contrast to the usual observation of the moments being close to parallel with the a-axis. This study also shows evidence that the electrical polarisation has a significant contribution from the valence electrons of the O ions, agreeing with previous work.

Diversos anodos para célula a combustível de óxido sólido (SOFC) têm sido estudados devido aos problemas de deterioração dos anodos tradicionalmente usados, os compósitos à base de zircônia estabilizada/Ni (YSZ/Ni). Estudos prévios evidenciaram que a perovskita La0,75Sr0,25Cr0,50Mn0,50O3 (LSCM) possui desempenho similar em SOFCs usando hidrogênio e metano como combustível, tornando essa cerâmica um possível substituto dos compósitos à base de níquel. No presente estudo, foram sintetizados compostos La0,75Sr0,25Cr0,50-xMn0,50- yRux,yO3 (LSCM-Ru) pelo método dos precursores poliméricos. Análises termogravimétrica e térmica diferencial (TG/ATD) simultâneas e difração de raios X (DRX) foram utilizadas para monitorar a evolução térmica das resinas precursoras e a formação de fase dos compostos. As propriedades elétricas de amostras sinterizadas foram estudadas pela técnica de 4 pontas de prova dc na faixa de temperatura entre 25 °C e 800 °C. Os resultados experimentais indicaram a formação de fase única dos compostos LSCM-Ru calcinados a ~1200 °C. Os parâmetros de rede, calculados a partir dos dados de DRX, revelaram que a substituição parcial dos íons Cr ou Mn pelo Ru não altera significativamente a estrutura cristalina do LSCM até x,y ~ 0,10; uma característica consistente com os raios iônicos similares dos cátions Cr, Mn e Ru com número de coordenação seis. Medidas de resistividade elétrica ao ar mostraram que o mecanismo de transporte não é alterado e que o efeito da substituição de Ru nas propriedades elétricas do composto depende do íon substituído (Cr ou Mn) de maneira consistente com suas substituições parciais. Os testes de SOFCs unitárias revelaram que células com os anodos constituídos por uma camada coletora de corrente do anodo cerâmico LSCM-Ru e uma camada funcional de YSZ/Ni têm desempenho superior a células contendo apenas o anodo cerâmico. As células contendo os anodos cerâmicos LSCM-Ru foram testadas em hidrogênio e etanol, entre 800 °C e 950 °C, e mostraram desempenho em etanol superior ao em hidrogênio; uma característica que foi associada às propriedades de transporte eletrônico dos compostos LSCM-Ru em atmosfera redutora. Os resultados sugerem que os compostos LSCM com substituição parcial de Ru são anodos promissores para SOFC operando com etanol. / Several anodes for solid oxide fuel cell (SOFC) have been studied because of serious degradation exhibited by the traditionally used yttria-stabilized zirconia/Ni cermets (YSZ/Ni). Previous studies showed that the perovskite La0.75Sr0.25Cr0.50Mn0.50O3 (LSCM) has similar performance in SOFCs running on hydrogen and methane fuels, making such a ceramic a potential alternative to YSZ/Ni cermets. In the present study, compounds La0.75Sr0.25Cr0.50- xMn0.50-yRux,yO3 (LSCM-Ru) were synthesized by the polymeric precursor method. Simultaneous thermogravimetric and differential thermal analysis (TG/DTA) and X-ray diffraction (XRD) were used to monitor the thermal evolution of the precursor resins and the formation of crystalline phases. The electrical properties of sintered samples were studied by the 4-probe dc technique in the temperature range between 25 °C and 800 °C with controlled atmosphere. The experimental results showed the formation of single phase LSCM-Ru compounds after heat treatment at ~ 1200 °C. Lattice parameters, calculated from the XRD data, revealed that the partial substitution of Cr or Mn by Ru has no significant effect on the crystal structure of LSCM up to Ru x,y ~ 0.10; in agreement with the similar ionic radius of Cr, Mn and Ru with coordination number six. Electrical resistivity measurements showed that the transport mechanism is unchanged and that the effect of Ru addition on the electrical properties of the compound depends on the substituted ion (Cr or Mn). Electrochemical tests of SOFCs demonstrated that single cells comprised of a current collector layer of LSCM-Ru ceramic anode and a functional layer for YSZ/Ni have superior performance when compared to single cells with only one layer of the ceramic anode. Single cells with the LSCM-Ru ceramic anode layer were tested under both hydrogen and ethanol fuels, in the 800 °C - 950 °C temperature range. The main results showed that the single fuel cells exhibited higher performance under ethanol than under hydrogen; a feature that was related to the enhanced electronic transport properties of LSCM-Ru in reducing atmosphere. The experimental results suggest that the LSCM-Ru compounds are promising anodes for ethanol fueled SOFCs.

Ce manuscrit présente l?étude par diffusion de neutrons aux petits angles des inhomogénéités magnétiques de l?échelle nanométrique à l?échelle mésoscopique à basse température dans les composés manganites à effet CMR de la série Pr1-xCaxMnO3, x proche de 1/3, et son évolution sous champ magnétique appliqué. <br />Ces systèmes montrent une séparation de phase à grande échelle entre une phase ferromagnétique isolante (FI) et une phase antiferromagnétique isolante (AFI) correspondant à deux phases cristallines distinctes. Ils se transforment en une troisième phase cristalline, ferromagnétique métallique (FM), sous l?effet du champ magnétique. Nous avons tenté de comprendre par quel mécanisme. <br />Nous avons mis en évidence l?existence d?inhomogénéités magnétiques nanométriques dans chacune des phases FI et AFI. Notre étude sous champ révèle l?apparition d?un fort signal de diffusion dû à une nucléation de clusters de phase FM mésoscopiques (quelques centaines de nanomètres) lors de la transition I-M induite par le champ, faisant ainsi disparaître la diffusion par les objets nanométriques. L?effet CMR n?est donc pas dû à une nucléation à l?échelle nanométrique mais mésoscopique.

Ce travail est consacré à l'étude des influences de deux cations, le cérium et le baryum, sur les propriétés structurales, physico-chimiques, électriques et électrochimiques de l'oxyde (La,Sr)(Cr,Mn)O3 (LSCM). L'effet de l'état d'oxydation du cérium a été déterminé en substituant les sites A de LSCM et d'un oxyde de composition proche, CexSr1-xCr0,5Mn0,5O3 (CeSCM). L'influence des propriétés de basicité du baryum a été examinée. Les matériaux sont stables en conditions de fonctionnement d'anode pour SOFC. La conductivité est de type p pour CeLSCM et CeSCM. Les composés LBCM sont des semi-conducteurs de type n pour des pressions partielles comprises entre 1 et 10-4 atm, et de type p pour des pressions plus faibles. Sous atmosphère neutre, la conductivité électrique totale augmente avec la teneur en cérium dans LSCM, et la conductivité des matériaux CeSCM est similaire à celle de CeLSCM substitué par 25% de cérium (36 S.cm-1 à 900 °C). Sous atmosphère réductrice, la conductivité des matériaux CeLSCM est de l'ordre de 1 S.cm-1. La quantité de baryum n'a pas d'influence sur la conductivité de LSBCM. La caractérisation d'électrodes ponctuelles denses a permis de montrer que les performances anodiques augmentent avec la teneur en cérium substitué au lanthane dans LSCM. La nature des processus impliqués n'est pas modifiée lorsque le strontium est substitué par le cérium, même si l'absence de lanthane pénalise le comportement anodique. Des performances intéressantes pour une application comme matériau d'anode pour SOFC ont été atteintes pour le composé La0,75Ba0,25Cr0,5Mn0,5O3. Les origines des contributions élémentaires des caractéristiques d'électrode sont discutées.

The high degree of modification through chemical substitution afforded by the perovskite crystal structure and its related counterparts allows a systematic study of structure-property relationships critical to understand the wide variety of exotic phenomena observed in these materials where the spin, charge, orbital, and lattice degrees of freedom are highly correlated. From the multiple phenomena observed in these materials, which includes multiferroicity, catalytic activity, and high temperature superconductivity, this study is concerned with a material that displays colossal magnetoresistance (CMR), La₂₋₂xSr₁₊₂xMn₂O₇; this is a naturally bilayered manganite that exhibits CMR at a paramagnetic to ferromagnetic transition that coincides with an insulator to metal transition. The strong correlation between different degrees of freedom in the material leads to considerable variation in its magnetic properties due to doping even in the small range studied of 0.32 [less than or equal to] x [less than or equal to] 0.4, where the easy axis of magnetization changes from the c-axis to the ab plane. Magnetic force microscopy (MFM) was used for this part of the work, to visualize the local variation of the out of plane (c-axis) magnetization or magnetic microstructure of La₂₋₂xSr₁₊₂xMn₂O₇ for 0.32 [less than or equal to] x [less than or equal to] 0.4 at the exposed ab surface and its evolution due to an applied magnetic field at 4 K. For the x = 0.32 composition, which is close to the out of plane to in plane magnetization transition, a strong preferred magnetization direction within the ab plane or magnetocrystalline anisotropy was observed. The stray magnetic field of the MFM tip perturbs the magnetic microstructure of low coercivity materials like diluted magnetic semiconductors, making it unsuitable for the study of such materials. For this reason, as part of this project a scanning Hall probe microscope (SHPM), a magnetic imaging technique complementary to MFM that uses a Hall sensor that provides a magnetically non-invasive calibrated measurement of the stray fields at the surface of a sample with good resolution (~ 1 [micrometer]), was designed. The construction of a compact cryogenic variable-temperature (77 - 300 K) SHPM, highlighting its features, is described. / text

Akustinių bangų ir šviesos – akustooptinė (AO) sąveika įgalina tirti akustinių bangų savybes ne tik kristalo paviršiuje, bet ir tūryje. Tai aktualu kuriant tūrinių bangų prietaisus įvairiems taikymams. Iki šiol yra atlikta keletas AO difrakcijos eksperimentų, kai sunertiniais keitikliais žadinamos tūrinės bangos, bet ne nuotėkio paviršinių akustinių bangų (PAB) spinduliuotė į tūrį. Kita vertus, AO sąveiką galima efektyviai panaudoti šviesos parametrų valdyme. Tūrinių bangų AO prietaisai – šviesos moduliatoriai, deflektoriai, derinami filtrai plačiai naudojami praktikoje. Šioje disertacijoje pateikiami anizotropinės šviesos difrakcijos nuotėkio paviršinių akustinių bangų spinduliuote į kristalo tūrį ZX-LiNbO3 ir YX-LiTaO3 eksperimentiniai rezultatai ir teorinis modelis. Tokio tipo sąveika įgalina suderinti sunertinių PAB keitiklių technologijos privalumus su didesniu šviesos sąveikos su tūrinėmis akustinėmis bangomis efektyvumu. Dėmesys mišraus valentingumo manganitams, turintiems perovskito kristalinę gardelę vis didėja dėl fazinio virsmo paramagnetikas – feromagnetikas Kiuri temperatūroje, milžiniškosios magnetovaržos efekto, didelės unikalių tarpusavyje susijusių savybių įvairovės ir potencialo įvairiuose taikymuose. Dėl stiprios Jahn-Teller tipo elektron-fononinės sąveikos akustiniai metodai yra perspektyvūs tiriant manganitus. Šioje disertacijoje pateikiami nuotėkio paviršinių akustinių bangų spinduliuotės į tūrį sklidimo dariniuose La0.67Sr0.33MnO3 plėvelė –... [toliau žr. visą tekstą] / Acoustic wave and light – acousto-optic (AO) interaction provides an efficient tool for probing the acoustic wave properties not only at a crystal surface but also at any point within its bulk. This is topical in the design of the bulk wave devices for various applications. Meanwhile, there have been a few investigations of AO diffraction by (interdigital transducer) IDT-generated bulk waves, but not of the diffraction due to the radiation from leaky surface acoustic waves (SAWs). On the other hand, AO interaction enables efficient control of light parameters. Bulk wave AO devices have found numerous applications as light modulators, deflectors, tunable filters. In this PhD thesis, the experimental investigation and theoretical model of anisotropic light diffraction by leaky SAW radiation into crystal bulk in ZX-LiNbO3 and YX-LiTaO3 are reported. This type of interaction allows one to combine benefits of the IDT technology with the enhanced interaction efficiency of bulk-wave-type interaction. Mixed-valence perovskite manganites were studied intensively in recent years due to the observed paramagnetic to ferromagnetic transition at Curie temperature, colossal magnetoresistance effect, a variety of unique properties and potential at various applications. Due to the strong Jahn-Teller electron-phonon coupling the acoustic technique is effective tool for investigations of manganites. In this PhD thesis, the experimental investigation of the leaky SAW radiation propagating in... [to full text]

Acoustic wave and light – acousto-optic (AO) interaction provides an efficient tool for probing the acoustic wave properties not only at a crystal surface but also at any point within its bulk. This is topical in the design of the bulk wave devices for various applications. Meanwhile, there have been a few investigations of AO diffraction by (interdigital transducer) IDT-generated bulk waves, but not of the diffraction due to the radiation from leaky surface acoustic waves (SAWs). On the other hand, AO interaction enables efficient control of light parameters. Bulk wave AO devices have found numerous applications as light modulators, deflectors, tunable filters. In this PhD thesis, the experimental investigation and theoretical model of anisotropic light diffraction by leaky SAW radiation into crystal bulk in ZX-LiNbO3 and YX-LiTaO3 are reported. This type of interaction allows one to combine benefits of the IDT technology with the enhanced interaction efficiency of bulk-wave-type interaction. Mixed-valence perovskite manganites were studied intensively in recent years due to the observed paramagnetic to ferromagnetic transition at Curie temperature, colossal magnetoresistance effect, a variety of unique properties and potential at various applications. Due to the strong Jahn-Teller electron-phonon coupling the acoustic technique is effective tool for investigations of manganites. In this PhD thesis, the experimental investigation of the leaky SAW radiation propagating... [to full text] / Akustinių bangų ir šviesos – akustooptinė (AO) sąveika įgalina tirti akustinių bangų savybes ne tik kristalo paviršiuje, bet ir tūryje. Tai aktualu kuriant tūrinių bangų prietaisus įvairiems taikymams. Iki šiol yra atlikta keletas AO difrakcijos eksperimentų, kai sunertiniais keitikliais žadinamos tūrinės bangos, bet ne nuotėkio paviršinių akustinių bangų (PAB) spinduliuotė į tūrį. Kita vertus, AO sąveiką galima efektyviai panaudoti šviesos parametrų valdyme. Tūrinių bangų AO prietaisai – šviesos moduliatoriai, deflektoriai, derinami filtrai plačiai naudojami praktikoje. Šioje disertacijoje pateikiami anizotropinės šviesos difrakcijos nuotėkio paviršinių akustinių bangų spinduliuote į kristalo tūrį ZX-LiNbO3 ir YX-LiTaO3 eksperimentiniai rezultatai ir teorinis modelis. Tokio tipo sąveika įgalina suderinti sunertinių PAB keitiklių technologijos privalumus su didesniu šviesos sąveikos su tūrinėmis akustinėmis bangomis efektyvumu. Dėmesys mišraus valentingumo manganitams, turintiems perovskito kristalinę gardelę vis didėja dėl fazinio virsmo paramagnetikas – feromagnetikas Kiuri temperatūroje, milžiniškosios magnetovaržos efekto, didelės unikalių tarpusavyje susijusių savybių įvairovės ir potencialo įvairiuose taikymuose. Dėl stiprios Jahn-Teller tipo elektron-fononinės sąveikos akustiniai metodai yra perspektyvūs tiriant manganitus. Šioje disertacijoje pateikiami nuotėkio paviršinių akustinių bangų spinduliuotės į tūrį sklidimo dariniuose La0.67Sr0.33MnO3 plėvelė –... [toliau žr. visą tekstą]

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.