Interface Combinatorial Pulsed Laser Deposition to Enhance Heterostructures Functional Properties

In this chapter we will describe a new development of combinatorial pulsed laser deposition (CPLD) which targets the exploration of interface libraries. The idea is to modulate continuously the composition of interfaces on a few atomic layers in order to alter their functional properties. This unique combinatorial synthesis of interfaces is possible due to very specific PLD characteristics. The first one is its well-known ability for complex oxide stoichiometry transfer from the target to the film. The second one is the layer by layer control of thin film growth at the atomic level using in-situ RHEED characterization. The third one relates to the directionality of the ablated plume which allows for selective area deposition on the substrate using a mobile shadow-mask. However PLD also has some limitations and important PLD aspects to be considered for reliable CPLD are reviewed. Multiple examples regarding the control of interface magnetism in magnetic tunnel junctions and energy band and Schottky barrier height tuning in ferroelectric tunable capacitors are presented

Why pinning by surface irregularities can explain the peak effect in transport properties and neutron diffraction results in NbSe2 and Bi-2212 crystals?

The existence of a peak effect in transport properties (a maximum of the critical current as function of magnetic field) is a well-known but still intriguing feature of type II superconductors such as NbSe2 and Bi-2212. Using a model of pinning by surface irregularities in anisotropic superconductors, we have developed a calculation of the critical current which allows estimating quantitatively the critical current in both the high critical current phase and in the low critical current phase. The only adjustable parameter of this model is the angle of the vortices at the surface. The agreement between the measurements and the model is really very impressive. In this framework, the anomalous dynamical properties close to the peak effect is due to co-existence of two different vortex states with different critical currents. Recent neutron diffraction data in NbSe2 crystals in presence of transport current support this point of view

Etude de la séparation de phase et polarisation de spins dans les manganites La0.8Sr0.2MnO3 par microscopie en champ proche et magnétotransport

Les composés manganites pérovskites sont des candidats potentiels pour des applications magnétiques et magnétorésistives. Ils connaissent un regain d intérêt ces dix dernières années et la croissance de monocristaux est devenue nécessaire pour mieux comprendre et améliorer l étude des propriétés physiques menées en amont sur des couches minces de mêmes compositions. A travers cette étude, nous nous sommes tout particulièrement intéressés au composé La0.8Sr0.2MnO3 élaboré dans un four à image par la technique de fusion de zone. Il présente ses propriétés les plus intéressantes au voisinage de la température ambiante. Les paramètres structuraux et texturaux ont été analysés par microscopie en champ proche, microscopie à balayage et en transmission. On a ainsi pu observer des macles sur toute la surface des échantillons et aussi des défauts amorphes de taille nanométrique, mais aucun joint de grain n a été relevé. Dans la partie centrale, ces derniers, en plus grand nombre, modifient les interactions magnétiques entre domaines. En revanche, sur le bord, comme la cristallinité est meilleure, le couplage magnétique est plus fort. Une mise en ordre des domaines magnétiques s impose alors selon un axe de facile aimantation. En transport, des effets de non linéarité dus au chauffage de type Joule ont été observés en régime de courant alternatif. Après avoir établi dans quelle gamme des valeurs de courant la réponse était linéaire, les propriétés intrinsèques des monocristaux de La0.8Sr0.2MnO3 ont été étudiées. Ainsi nous avons mis en évidence des phénomènes de relaxation de la résistance à température ambiante. Par mesure de résistance locale, la coexistence de phase entre amas métalliques et matrice isolante a été montrée. Ceci permet d interpréter nos mesures de transport en termes de percolation de domaines. Pour finir, en régime de courant continu, nous avons mis en évidence que, près de la température de Curie, les électrons conducteurs, polarisés en spin suivant la direction d aimantation des domaines ferromagnétiques forts, retournent, sous l effet d un couple magnétique, les moments des domaines ferromagnétiques faibles de façon continue et réversible, pouvant générer une hausse de 30% de l aimantation dans le matériau.Perovskite manganite compounds are potential candidates for magnetic and magnetoresistive applications. They have known a resurge in interest during the last ten years and the growth of single crystals has become necessary to better understand and improve the study of the physical properties carried out on thin films of the same composition. In the present work, we were quite particularly interested in the La0.8Sr0.2MnO3 compound elaborated in an image furnace by the floating zone technique. Its most exciting properties can in fact be studied at room temperature. The structural and textural parameters were analyzed by near field microscopy, as well as by scanning and transmission microscopy. We were thus able to observe twins on the surface of all samples and also amorphous defects of nanometric size, but no grain boundaries were found. Concentrated mainly in the central part of the material, these modify the magnetic interactions between domains. On the other hand, near the edges, as the crystal structure is better maintained, the magnetic coupling is stronger. An ordering of the magnetic domains could be found, along an axis of easy magnetization. In transport, experiments non-linear effects due to Joule heating were observed in the alternating current regime. Having established in which range of current values the response was linear, the intrinsic properties of the La0.8Sr0.2MnO3 single crystals were studied, for example, relaxation phenomena of the resistance at room temperature. By measuring the spreading resistance, the phase coexistence between metallic clusters and an insulating matrix was revealed. This allows us to interpret our transport measurements in terms of percolation of ferrometallic domains. To finish, in the direct current regime, we show that, near the Curie point, the conduction electrons, spin-polarized according to the magnetization direction of hard ferromagnetic domains, flip, under the influence of a magnetic torque, the moments of soft ferromagnetic domains in a continuous and reversible way, being able thereby to lead to an enhancement of up to 30 % of the magnetization in the material.TOURS-Bibl.électronique (372610011) / SudocSudocFranceF

Room temperature ferromagnetism in anatase Ti0.95V0.05O2 thin films

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Substrate effects on the room-temperature ferromagnetism in Co-doped TiO2 thin films grown by pulsed laser deposition

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Room temperature ferromagnetism in laser ablated transition-metal-doped TiO 2 thin films on various types of substrates

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Room temperature ferromagnetism in anatase Ti0.95Cr0.05O2 thin films: Clusters or not?

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Room temperature ferromagnetism in anatase Ti0.95Cr0.05O2 thin films: Clusters or not?

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Correlation between crystallinity and magnetism in a series of laser-ablated anatase Ti 1 x Co x O 2 thin films

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Laser ablated Ni-doped HfO_2 thin films: Room temperature ferromagnets

Laser ablated Ni-doped HfO_2 thin films fabricated under a wide range of growth conditions all showed ferromagnetism above room temperature. However, the films deposited at 800 °C under an oxygen partial pressure of 10^ Torr have the largest magnetic moment of 2.7μB/ Ni. Ni-doped HfO_2 films also well demonstrate a large anisotropy. Magnetic force microscopy measurements confirmed that Ni-doped HfO2 films are real room temperature ferromagnets with a domain structure, and that the size of magnetic domains is larger than 10 μm