(La0.67Sr0.33MnO3)£»(SrO), LSMO214(n=1) in short, is 2-D magnetic insulator with a structure very similar to the 3D La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3, 113(n=1) in short, which consists of superstructure of a subsequent magnetic layers and insulating layers. Forming a single 214 phase bulk is not easy, a mix phase of 2<n<¡Û compounds is usually seen. Due to the lattice mismatch between Substrate and bulk,strain has been an important factors of magnetic resistance and electrical properties. Studying single layer and multi-layer films,we find because the small of growth condition scope and lattice mismatch,the LSMO214 films consists mix phases of higher n.

Abstract The interaction between the multilayer of Antiferromagnetic(AFM)/ Ferromagnetic(FM) film have been one of the focal point in scientific and technology. In our preliminary result the enhancement on the low field magnetoresistance of AFM-La0.67Sr1.33MnO4 and FM-La0.67Ca0.33MnO3 mixture is obvious. It is, therefore, worthwhile to make it into a form of multilayer as the tunneling magnetoresistance (TMR) structure. This project was planed to start at a bilayer film of AFM-La0.67Sr1.33MnO4/ FM-La0.67Ca0.33MnO3 on SrTiO3(100) substrate by an off-axis RF sputtering system. Experiment at high temperature region (T¡Ö70K) exhibits normal colossal magnetoresistance (CMR) behavior. A small cusp appears in R-T curve between 50~70K which is believed due to the quantum fluctuation initiated from AFM layer acted on the AFM/FM interface. However, the MR properties at this region shows abnormal phenomenon. The MR curve strongly depends on the sample posture during measurement when the relative geometry between the applied field, the applied current and the sample surface is fixed. The reason of this abnormal phenomenon is not clear yet and worth for further study .

High quality perovskite manganites, La1-xAxMnO3 (A = Ca, Sr, Ba) are very attractive materials due to their great application potential for magnetic memory, uncooled infrared (IR) microbolometer and spintronics devices. This thesis presents studies of the growth and material characterization (including structural, electrical, magnetic and noise) of epitaxial manganite films on Si and GaAs. Furthermore, investigations about strain effect on structural and electrical properties of manganites, and finally fabrication of self-supported free standing microstructures for uncooled IR bolometer are also demonstrated. To obtain high quality epitaxial manganite films on semiconductor substrates at room temperature, using a combination of La0.67Sr0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) compounds, La0.67(Sr,Ca)0.33MnO3 (LSCMO) films were successfully grown on Si substrates with Bi4Ti3O12(BTO)/CeO2/YSZ buffers by pulsed laser deposition (PLD) technique. Crystallographic relations between layers shows cube-on-cube for BTO/CeO2/YSZ/Si and diagonal-on-side for LSCMO films on BTO layer. 4.4 %K-1 maximum temperature coefficient of resistivity (TCR = 1/ρ·dρ/dT) and 2.9 %kOe-1 colossal magnetoresistance (CMR) were obtained at room temperature. Assuming of a prototype of temperature sensor, 1.2 μK/√Hz of noise equivalent temperature difference (NETD) and 2.9×108 cm√Hz/W of detectivity are expected to achieve at 294 K, 30 Hz. For GaAs substrates, using MgO buffer layer, LCMO films shows 9.0 %K-1 of TCR at 223 K while LSMO exhibits 2 %K-1 at 327 K. Systematic strain effects on structural and electrical properties of La0.75Sr0.25MnO3 LSMO) films on BTO/CeO2/YSZ-buffered Si, Si1-xGex/Si (compressive strain, x = 0.05-0.20) and Si1-yCy/Si (tensile, y = 0.01) were investigated. The strain induced from Si1-xGex/Si and Si0.99C0.01/Si has a tendency to decrease the roughness of CMR films compared to Si sample. High resistivity and low TCR values are observed for Si0.8Ge0.2/Si and Si0.99C0.01/Si samples due to excessive strains whereas Si0.9Ge0.1/Si and Si0.95Ge0.05/Si show slight improvements of films quality and TCR value. To fabricate LSCMO manganite bolometer on Si, wet etching with KOH and BHF and dry etching methods with Ar ion beam etching (IBE) were studied. For KOH wet etching, LSCMO films show high chemical resistance with lower than 0.2 nm/min of etch rate. BHF wet etching shows high etching selectivity over photoresist mask and silicon substrates. The etch rates for LSCMO and BTO layers are 22 and 17 nm/min. For Ar IBE, LSCMO films and oxide buffer layers show similar etch rates, 16-17 nm/min that are lower compared to 24 nm/min for Si. Free standing, self-supported heteroepitaxial LSCMO/BTO/CeO2/YSZ membranes for bolometer pixels on Si was successfully fabricated by Ar IBE and ICP etching techniques using a preannealed photoresist. The structural investigation by TEM revealed the sharp interfaces between layers. The electrical property of the free standing membrane was slightly degraded due to strain release and multi-step etching effect. These results demonstrate feasibility to use heteroepitaxial oxide structures as a thermally isolated membrane with conventional photoresist patterning. / QC 20101101

<p>High quality perovskite manganites, La1_-xA_xMnO₃ (A = Ca, Sr, Ba) are very attractive materials due to their great application potential for magnetic memory, uncooled infrared (IR) microbolometer and spintronics devices. This thesis presents studies of the growth and material characterization (including structural, electrical, magnetic and noise) of epitaxial manganite films on Si and GaAs. Furthermore, investigations about strain effect on structural and electrical properties of manganites, and finally fabrication of self-supported free standing microstructures for uncooled IR bolometer are also demonstrated.</p><p>To obtain high quality epitaxial manganite films on semiconductor substrates at room temperature, using a combination of La_0.67Sr₀.₃₃MnO₃(LSMO) and La_0.67Ca_0.33MnO₃(LCMO) compounds, La_0.67(Sr,Ca)_0.33MnO₃ (LSCMO) films were successfully grown on Si substrates with Bi₄Ti₃O₁₂(BTO)/CeO₂/YSZ buffers by pulsed laser deposition (PLD) technique. Crystallographic relations between layers shows cube-on-cube for BTO/CeO2/YSZ/Si and diagonal-on-side for LSCMO films on BTO layer. 4.4 %K^-1maximum temperature coefficient of resistivity (TCR = 1/ρ·dρ/dT) and 2.9 %kOe^-1 colossal magnetoresistance (CMR) were obtained at room temperature. Assuming of a prototype of temperature sensor, 1.2 μK/√Hz of noise equivalent temperature difference (NETD) and 2.9×10⁸ cm√Hz/W of detectivity are expected to achieve at 294 K, 30 Hz. For GaAs substrates, using MgO buffer layer, LCMO films shows 9.0 %K^-1 of TCR at 223 K while LSMO exhibits 2 %K^-1 at 327 K.</p><p>Systematic strain effects on structural and electrical properties of La₀.₇₅Sr_0.25MnO₃ LSMO) films on BTO/CeO2/YSZ-buffered Si, Si_1-xGe_x/Si (compressive strain, x = 0.05-0.20) and Si_1-yC_y/Si (tensile, y = 0.01) were investigated. The strain induced from Si_1-xGe_x/Si and Si_0.99C_0.01/Si has a tendency to decrease the roughness of CMR films compared to Si sample. High resistivity and low TCR values are observed for Si_0.8Ge₀.₂/Si and Si_0.99C_0.01/Si samples due to excessive strains whereas Si₀.₉Ge_0.1/Si and Si_0.95Ge_0.05/Si show slight improvements of films quality and TCR value.</p><p>To fabricate LSCMO manganite bolometer on Si, wet etching with KOH and BHF and dry etching methods with Ar ion beam etching (IBE) were studied. For KOH wet etching, LSCMO films show high chemical resistance with lower than 0.2 nm/min of etch rate. BHF wet etching shows high etching selectivity over photoresist mask and silicon substrates. The etch rates for LSCMO and BTO layers are 22 and 17 nm/min. For Ar IBE, LSCMO films and oxide buffer layers show similar etch rates, 16-17 nm/min that are lower compared to 24 nm/min for Si.</p><p>Free standing, self-supported heteroepitaxial LSCMO/BTO/CeO₂/YSZ membranes for bolometer pixels on Si was successfully fabricated by Ar IBE and ICP etching techniques using a preannealed photoresist. The structural investigation by TEM revealed the sharp interfaces between layers. The electrical property of the free standing membrane was slightly degraded due to strain release and multi-step etching effect. These results demonstrate feasibility to use heteroepitaxial oxide structures as a thermally isolated membrane with conventional photoresist patterning.</p>

L’objectif de la thèse est de développer un système de type jonction tunnel tout oxyde à base de La2/3Sr1/3MnO3 (LSMO) où il serait possible de contrôler l’aimantation des électrodes magnétiques par des processus à faible consommation d’énergie. Des jonctions tunnel épitaxiées de LSMO/SrTiO3/LSMO ont été obtenues montrant un double renversement de l’aimantation à température ambiante et un taux de magnétorésistance de 71 % à 10 K. En exerçant une contrainte sur le LSMO par le substrat il a été possible de moduler l’anisotropie des couches magnétiques. Des anisotropies perpendiculaire ou dans le plan ont pu être obtenues. Afin de contrôler le renversement des moments magnétiques dans une des électrodes ferromagnétiques trois options ont été envisagées : l’utilisation de l’injection de spin à partir d’un métal à fort couplage spin-orbite (Pt, Ir) ou d’un oxyde contenant de tels ions (ici Ru dans SrRuO3), et l’utilisation du Bi2FeCrO6, un oxyde multiféroïque pouvant présenter un couplage magnétoélectrique. Malgré des résultats prometteurs, aucune solution n’a permis des tests sur des jonctions afin d’estimer leur efficacité. L’objectif final n’est pas encore atteint mais des avancées intéressantes ont été faites afin d’envisager des dispositifs permettant le stockage et la manipulation de l’information. / The objective of this work is to develop La2/3Sr1/3MnO3 (LSMO) based all-oxide magnetic tunnel junction systems where it would be possible to control the magnetization of magnetic electrodes by low energy consumption processes. Epitaxial tunnel junctions of LSMO/SrTiO3/LSMO were obtained showing a double magnetization switching at room temperature and a magnetoresistance ratio of 71 % at 10 K. Using strain engineering, it was possible to modulate the anisotropy of the LSMO magnetic layers. Perpendicular or in plane anisotropies could be thus obtained. In order to control the reversal of the magnetic moments in one of the ferromagnetic electrodes three options were considered : the use of spin injection from a metal with a strong spin-orbit coupling (Pt, Ir) or an oxide containing this type of ions (here Ru in SrRuO3), and the use of Bi2FeCrO6 multiferroic oxide that may exhibit a magnetoelectric coupling. Despite promising results, no solution has allowed tests on junctions to be carried out to estimate their effectiveness. Although the final objective is not yet achieved, interesting progress has been made on the way to information storage and manipulation devices.

In der vorliegenden Arbeit werden durch den inversen piezoelektrischen Effekt kontrolliert Dehnungen in Lanthanmanganatschichten eingebracht und ihr Einfluss auf die Eigenschaften der Schichten untersucht. Dazu wird im ersten Teil der Arbeit ein Zweischichtsystem bestehend aus einer Manganatschicht aus La0,7Sr0,3MnO3, La0,8Ca0,2MnO3 oder La0,7Ce0,3MnO3 und einer piezoelektrischen Schicht aus PbZr0,52Ti0,48O3 untersucht. Der epitaktisch auf Einkristallsubstraten abgeschiedene Aufbau entspricht einer Feldeffekt-Transistor-Struktur. Neben den Effekten der Dehnung auf den elektrischen Widerstand der Manganatschicht wird auch der elektrische Feldeffekt untersucht. Durch mechanische Klemmung des Substrats können nur kleine Dehnungen in die Manganatschichten eingebracht werden. Um größere und homogene Dehnungen steuerbar in Manganatschichten einzubringen, werden im zweiten Teil der Arbeit La0,7Sr0,3MnO3 - Schichten auf piezoelektrischen Einkristallsubstraten der Verbindung (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3 mit x = 0,28 epitaktisch abgeschieden. Der Einfluss von mechanischen Dehnungen von bis zu 0,1% auf den elektrischen Transport, die ferromagnetische Übergangstemperatur und die Magnetisierung kann so eingehend untersucht werden. Es wird ein außergewöhnlich großer Einfluss von Dehnungen auf die Eigenschaften von La0,7Sr0,3MnO3 gefunden. / In this work, strain arising from the inverse piezoelectric effect is induced into lanthanum manganite thin films in order to change and control their properties. In the first part of this work, manganite films of the compositions La0.7Sr0.3MnO3, La0.8Ca0.2MnO3 or La0.7Ce0.3MnO3 are combined with a piezoelectric layer of the composition PbZr0.52Ti0.48O3 in a bilayer system. This structure is grown epitaxially on single crystal substrates and corresponds to a field-effect transistor setup. Besides effects of strain on the electrical resistance of the manganite layers, field effects are observed. Due to clamping of the substrate, only small strains can be induced to the manganite films. In order to apply larger and homogeneous controllable strain to the manganite layers, thin films of La0.7Sr0.3MnO3 are grown epitaxially on piezoelectric single crystal substrates of the composition (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3, x = 0.28. Strain levels up to 0.1% are reached. The influence of the strain on electrical transport, ferromagnetic transition temperature and magnetization is analyzed. A remarkably large influence of the strain on the properties of La0.7Sr0.3MnO3 is found.

In der vorliegenden Arbeit werden durch den inversen piezoelektrischen Effekt kontrolliert Dehnungen in Lanthanmanganatschichten eingebracht und ihr Einfluss auf die Eigenschaften der Schichten untersucht. Dazu wird im ersten Teil der Arbeit ein Zweischichtsystem bestehend aus einer Manganatschicht aus La0,7Sr0,3MnO3, La0,8Ca0,2MnO3 oder La0,7Ce0,3MnO3 und einer piezoelektrischen Schicht aus PbZr0,52Ti0,48O3 untersucht. Der epitaktisch auf Einkristallsubstraten abgeschiedene Aufbau entspricht einer Feldeffekt-Transistor-Struktur. Neben den Effekten der Dehnung auf den elektrischen Widerstand der Manganatschicht wird auch der elektrische Feldeffekt untersucht. Durch mechanische Klemmung des Substrats können nur kleine Dehnungen in die Manganatschichten eingebracht werden. Um größere und homogene Dehnungen steuerbar in Manganatschichten einzubringen, werden im zweiten Teil der Arbeit La0,7Sr0,3MnO3 - Schichten auf piezoelektrischen Einkristallsubstraten der Verbindung (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3 mit x = 0,28 epitaktisch abgeschieden. Der Einfluss von mechanischen Dehnungen von bis zu 0,1% auf den elektrischen Transport, die ferromagnetische Übergangstemperatur und die Magnetisierung kann so eingehend untersucht werden. Es wird ein außergewöhnlich großer Einfluss von Dehnungen auf die Eigenschaften von La0,7Sr0,3MnO3 gefunden. / In this work, strain arising from the inverse piezoelectric effect is induced into lanthanum manganite thin films in order to change and control their properties. In the first part of this work, manganite films of the compositions La0.7Sr0.3MnO3, La0.8Ca0.2MnO3 or La0.7Ce0.3MnO3 are combined with a piezoelectric layer of the composition PbZr0.52Ti0.48O3 in a bilayer system. This structure is grown epitaxially on single crystal substrates and corresponds to a field-effect transistor setup. Besides effects of strain on the electrical resistance of the manganite layers, field effects are observed. Due to clamping of the substrate, only small strains can be induced to the manganite films. In order to apply larger and homogeneous controllable strain to the manganite layers, thin films of La0.7Sr0.3MnO3 are grown epitaxially on piezoelectric single crystal substrates of the composition (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3, x = 0.28. Strain levels up to 0.1% are reached. The influence of the strain on electrical transport, ferromagnetic transition temperature and magnetization is analyzed. A remarkably large influence of the strain on the properties of La0.7Sr0.3MnO3 is found.

With recent trends in miniaturization in the electronics sector, ferroelectrics have gained popularity due to their applications in non-volatile RAM. Taking one step further researchers are now exploring multiferroic devices that overcome the drawbacks of ferroelectric (FE) and ferromagnetic (FM) RAM’s while retaining the advantages of both. The work presented in this dissertation focuses on the growth of FE and FM thin film structures. The primary goals of this work include, (1) optimization of the parameters in the pulsed laser deposition (PLD) of FE and FM films and their heterostructures, (2) development of a structure-property relation that leads to enhancements in electric and magnetic polarizations of these structures, (3) investigation of doping on further enhancement of polarizations and coupling between the FE and FM layers. The materials of choice are La0.7Sr0.3MnO3 (LSMO) as the ferromagnetic and PbZr0.52Ti0.48O3 (PZT) as the ferroelectric component. Epitaxial thin film capacitors were grown using PLD. The work starts with the establishment of the optimum deposition conditions for PZT and goes on to describe results of attempts at performance enhancement and tuning using two methods. It is demonstrated that ferroelectric and ferromagnetic properties can be tuned by inserting a ferromagnetic buffer layer of CoFe2O4 (CFO) between PZT and LSMO. One of the key findings of this work was the anomalously high ferroelectric polarizations produced by lanthanum (La) doped PZT films. This work attempts to shine light on a possible mechanism that leads to such high enhancements in polarization.

In this dissertation, we have used a combination of synchrotron-based x-ray spectroscopic, scattering and imaging techniques to investigate the electronic, magnetic and structural properties of materials and material systems which exhibit natural as well as engineered nanoscale structural distortions. In order to investigate the interplay between the above-mentioned degrees of freedom with spatial and depth resolution, we have utilized non-destructive techniques, such as x-ray absorption spectroscopy (XAS), polarization-dependent photoemission electron microscopy (PEEM), nanoscale scanning x-ray diffraction microscopy (nano-SXDM) and standing-wave x-ray photoemission spectroscopy (SW-XPS). The results were compared to several types of state-of-the-art first-principles theoretical calculations. In the first part of the dissertation, we have investigated the nanoscale magneto-elastic structure of the Fe3Ga magnetic alloy, which was recently reported to exhibit non-volume conserving magnetostriction. As the result of our combined PEEM and nano-SXDM study, we have discovered the structural basis for this phenomenon – periodic long-wavelength (~269 nm) elastic domain walls, with domains (regions of zero-strain) existing as narrow transition regions. Atto-scale elastic gradients and self-strain across the elastic domain walls were quantitatively measured and imaged by nano-SXDM. Our measurements revealed that the gradients inside the elastic walls are accommodated by gradually increasing/decreasing inter-planar spacing resembling a longitudinal wave. Our element-specific polarization-dependent PEEM measurements revealed that the magnetic structure of the crystal modulates with similar periodicity (~255 nm), and the resulting magneto-elastic coupling produces a ‘giant’ field-induced bulk deformation, which is equal to the measured self-strain of the elastic domain wall. In the second part of this dissertation, we utilized a combination of soft x-ray standing-wave photoemission spectroscopy (SW-XPS), hard x-ray photoemission spectroscopy (HAXPES) and scanning transmission electron microscopy (STEM) to probe the depth-dependent and single-unit-cell resolved electronic structure of isovalent manganite superlattices (Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3)15 wherein the electronic and magnetic properties are intentionally modulated with depth via engineered O octahedral rotations and A-site displacements. Standing-wave-excited spectroscopy of the Mn 2p and O 1s core-levels confirmed the isovalent nature of the Mn ions in the superlattice and revealed significant depth-dependent variations in the local chemical and electronic environment around the O atoms, consistent with the state-of-the-art theoretical calculations. Furthermore, it was shown that a surface relaxation and orbital reconstruction in the several top Eu0.7Sr0.3MnO3 atomic layers produces substantial changes in the observed electronic structure, which, according to the first-principles theoretical calculations, occur due to the establishment of orbital stripe order in the top unit cell. In summary, we have used synchrotron-based x-ray spectroscopic and microscopic techniques, in conjunction with high-resolution electron microscopy, to study the electronic, magnetic and structural properties of advanced functional materials exhibiting strong nanoscale heterogeneity. We discovered a strong coupling between the nanoscale structural and magnetic properties in the non-conventional magnetostrictive Fe3Ga single crystal. Our results suggest that this coupling provides the fundamental basis for the non-conventional magnetostriction phenomenon in this material. We have also discovered that the electronic properties of the Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3 superlattices can be epitaxially tuned via engineered A-site cation displacement, which is a result of the strong interfacial coupling between the Eu0.7Sr0.3MnO3 and La0.7Sr0.3MnO3 layers. This suggests a new way of tailoring and spatially-confining electronic and ferroic behavior in complex oxide heterostructures and creating novel ordered surface-reconstruction effects. / Physics

Low-temperature magnetic force microscopy was used to study the phase diagram of a La1/3Pr1/3Ca1/3MnO3 thin film grown on a (110) NdGaO3 (NGO) substrate by pulsed laser deposition. Traditionally, one can observe the phase change at the nanoscale level as the sample is cooled from room temperature through the transition temperature to liquid nitrogen temperatures, but in this case a fixed voltage ranging from 0 V to 31 V was applied before each cooling cycle. From in and ex situ transport measurements, it is observed that the temperature of the peak of the transition increases with applied field; however, the MFM images show that the magnetic transition begins at a lower temperature with the same increase in field. Thus, this dissertation shows that a new voltage control exists for the phase transition in certain manganites. / text