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Magnetism in wide band gap materials is of great interests for future spintronic device applications. We prepared MgO and Fe-doped MgO films ‘in-situ’ on substrates by inkjet printing, and investigated the ferromagnetism tuned by the doping of Fe, the annealing temperature and the film thickness. It is found that the Fe-doping improves the crystallinity of the films with lattice structure changed by annealing temperature. The saturation magnetization (Ms) of the films enhanced by ~5 times comparing with the pure MgO thin film of similar thickness (~90 nm), because of both the long-range ordering of localized 3d electrons in Fe and the defects induced magnetism. The Ms at 5 K decreases with the film thickness, which is mainly attributed to the interface induced ferromagnetism. The Fe-doped MgO films with ferromagnetism in this work can be used in future spintronic devices.

Contains a brief course of lectures, tasks for practical classes, questions for self-control and tests on all sections of the accounting of assets. Also includes cross-cutting goal to conduct training practices for professional module PM.01 "Documenting of economic operations and accounting of the assets of the organization." Meets the requirements of Federal state educational standards of secondary professional education of the last generation. For students of secondary vocational institutions, students majoring in 38.02.01 "Economy and accounting (on branches)".

A heterogeneous catalyst, magnesium zirconate (Mg2Zr5O12) was synthesized by co-precipitation and was used for biodiesel production via transesterification. Kusum oil was used as a feedstock. Catalyst characterization was accomplished by TGA, XRD, ATR FTIR, SEM, and EDX. The parameters viz. particle size, zeta potential, BET surface area and basicity of the catalyst were also determined. Characterization of catalyst supports the formation of single phase Mg2Zr5O12 and the catalyst was able to catalyse the transesterification reaction for economically viable biodiesel production. Various reaction parameters such as molar ratio (methanol: oil), catalyst concentration and reaction time were optimized in presence of Mg2Zr5O12 by using Response Surface Methodology (RSM) based on Box-Behnken design. The catalyst was reusable up to seven runs with ∼75% conversion in the seventh run. Maximum conversion of 97.98% FAME was obtained at 18:1 M ratio (methanol: oil), 2.5 wt% of catalyst at 65 °C temperature for 150 min. Physicochemical properties of FAME were also studied as per ASTM standard method.

First-principles calculations are performed using density function theory to explore the effects of dopant Ca in ceria (Ce1-xCaxO2-δ). The impact of oxygen vacancy on band gap and density of states is examined in doped ceria using generalized gradient approximations. Vacancy association and vacancy formation energies of the doped ceria are calculated to reveal the effect of dopant on ion conduction. The experimental study of the sample (Ce0.875Ca0.125O2-δ) was performed to compare with the theoretical results. The obtained results from theoretical calculation and experimental techniques show that oxygen vacancy increases the volume, lattice constant (5.47315 A) but decrease the band gap (1.72 eV) and bulk modulus. The dopant radius (1.173 A) and lattice constant (5.4718 A) are also calculated by equations which is close to the DFT lattice parameter. The result shows that oxygen vacancy shifts the density of states to lower energy region. Band gap is decreased due to shifting of valence states to conduction band. Vacancy formation shows a significance increase in density of states near the Fermi level. Density of states at Fermi level is proportional to the conductivity, so an increase in density of states near the Fermi level increases the conductivity. The experimental measured ionic conductivity is found to 0.095 S cm−1 at 600 °C. The microstructural studies is also reported in this work.

The efficient conversion of solid carbon fuels into energy by reducing the emission of harmful gases is important for clean environment. In this regards, direct carbon fuel cell (DCFC) is a system that converts solid carbon directly into electrical energy with high thermodynamic efficiency (100%), system efficiency of 80% and half emission of gases compared to conventional coal power plants. This can generate electricity from any carbonaceous fuel such as charcoal, carbon black, carbon fiber, graphite, lignite, bituminous coal and waste materials. In this paper, ternary carbonate-samarium doped ceria (LNK-SDC) electrolyte has been synthesized via co-precipitation technique, while LiNiCuZnFeO (LNCZFO) electrode has been prepared using solid state reaction method. Due to significant ionic conductivity of electrolyte LNK-SDC, it is used in DCFC. Three types of solid carbon (lignite, bituminous, sub-bituminous) are used as fuel to generate power. The X-ray diffraction confirmed the cubic crystalline structure of samarium doped ceria, whereas XRD pattern of LNCZFO showed its composite structure. The proximate and ultimate coal analysis showed that fuel (carbon) with higher carbon content and lower ash content was promising fuel for DCFC. The measured ionic conductivity of LNK-SDC is 0.0998 Scm−1 and electronic conductivity of LNCZFO is 10.1 Scm−1 at 700 °C, respectively. A maximum power density of 58 mWcm−2 is obtained using sub-bituminous fuel.

Lead-free alkali niobates Na 0.5 K 0.5 NbO 3 (NKN) ceramics, with significantly enhanced ferroelectric remanent polarization ( P r ), were prepared using Spark Plasma Sintering (SPS). Three types of boundaries were observed in the ceramics, being grain boundaries between faceted grains, domain boundaries that separate ferroelectric domains inside individual grains, and nanoscale sub-grain boundaries that reveal the nano-scale mosaicity of individual grains. Part of the sub-grain boundaries were from initial powder particles. The other sub-grain boundaries were built by ordered coalescence of nano-crystals during rapid SPS process. It was worthwhile to emphasize that the ordered coalescence of nano-crystals in bulk ceramics during sintering takes place and completes within minutes. These sub-grain features would disappear at higher temperature by long time sintering. Rapid Spark Plasma Sintering allowed us to capture this transient microstructure. The significantly enhanced ferroelectric P r of NKN was attributed to nanoscale sub-boundaries, which stimulated the dynamics of ferroelectric domain formation and switching.

Solution processed homogeneous (200) oriented MgO ∼85 nm thin films deposited on Si substrates were fabricated by inkjet printing. These films are found to show ferromagnetic order beyond room temperature with a saturation magnetization MS as high as ∼0.63 emu/g for the acid ink precursor. X-ray photoelectron spectroscopy investigations show the absence of any possible contamination effects, and confirm that the role of defect structure at the Mg site forming in acid condition is important for the observed magnetism.

We present a nanofabrication process for producing tungsten zone plates used in hard X-ray applications including a method of integrating a high-energy absorbing central stop with the optic. Tungsten zone plates are structured with electron-beam lithography and subsequent reactive ion etching. The central stop originates from a platinum wire. It is cut to dimension by focused ion beam etching, and afterwards attached to the zone plate center using ion beam induced deposition of platinum. A zone plate with integrated central stop will simplify alignment in hard X-ray scanning microscope arrangements where the 0th order light must be eliminated. The focusing performance of the zone plate device was investigated by scanning coherent diffraction imaging (ptychography) at 8 keV photon energy. We could demonstrate a diffraction-limited focus size of 53 nm diameter full-width-at-half-maximum. Tungsten zone plates with integrated central stops show promising results for use in hard X-ray microscopes at high-brightness facilities. QC 20140228

ZnO is a wide-band gap semiconductor widely used in optical and electric devices, associating with ferromagnetism at low dimension endowing its possibility for functional applications with magneto- ...

Thin films of nanocrystalline MgO were deposited on glass/Si substrates by rf/dc sputtering from metallic Mg, and ceramic MgO targets. The purpose of this study is to identify the differences in the properties, magnetic in particular, of MgO films obtained on sputter deposition from 99.99% pure metallic Mg target in a controlled Nitrogen + Oxygen partial pressure (O(2)pp)] atmosphere as against those deposited using an equally pure ceramic MgO target in argon + identical oxygen ambience conditions while maintaining the same total pressure in the chamber in both cases. Characterization of the films was carried out by X-ray diffraction, focussed ion beam cross sectioning, atomic force microscopy and SQUID-magnetometry. The `as-obtained' films from pure Mg target are found to be predominantly X-ray amorphous, while the ceramic MgO target gives crystalline films, (002) oriented with respect to the film plane. The films consisted of nano-crystalline grains of size in the range of about 0.4 to 4.15 nm with the films from metallic target being more homogeneous and consisting of mostly subnanometer grains. Both the types of films are found to be ferromagnetic to much above room temperature. We observe unusually high maximum saturation magnetization (MS) values of 13.75 emu/g and similar to 4.2 emu/g, respectively for the MgO films prepared from Mg, and MgO targets. The origin of magnetism in MgO films is attributed to Mg vacancy (V-Mg), and 2p holes localized on oxygen sites. The role of nitrogen in enhancing the magnetic moments is also discussed.

Direct printing of functional oxide thin films could provide a new route to low-cost, efficient and scalable fabrications of electronic devices. One challenge that remains open is to design the inks with long term stability for effective deposition of specific oxide materials of industrial importance. In this paper, we introduce a reliable method of producing stable inks for ‘in-situ’ deposition of oxide thin films by inkjet printing. The inks were prepared from metal-acetates solutions and printed on a variety of substrates. The acetate precursors were decomposed into oxide films during the subsequent calcination process to achieve the ‘in-situ’ deposition of the desired oxide films directly on the substrate. By this procedure we have obtained room temperature contamination free ferromagnetic spintronic materials like Fe doped MgO and ZnO films from their acetate(s) solutions. We find that the origin of magnetism in ZnO, MgO and their Fe-doped films to be intrinsic. For a 28 nm thick film of Fe-doped ZnO we observe an enhanced magnetic moment of 16.0 emu/cm3 while it is 5.5 emu/cm3 for the doped MgO film of single pass printed. The origin of magnetism is attributed to cat-ion vacancies. We have also fabricated highly transparent indium tin oxide films with a transparency >95% both in the visible and IR range which is rather unique compared to films grown by any other technique. The films have a nano-porous structure, an added bonus from inkjetting that makes such films advantageous for a broad range of applications.

MgO is a widely used material in ceramic and electronic industry. It is a well known insulator which has been used as a spacer layer in electronic circuits and magnetic tunnel junctions. We report ...

A method for additive layer-by-layer fabrication of arbitrarily shaped 3D silicon micro- and nanostructures is reported. The fabrication is based on alternating steps of chemical vapor deposition of silicon and local implantation of gallium ions by focused ion beam (FIB) writing. In a final step, the defined 3D structures are formed by etching the silicon in potassium hydroxide (KOH), in which the local ion implantation provides the etching selectivity. The method is demonstrated by fabricating 3D structures made of two and three silicon layers, including suspended beams that are 40 nm thick, 500 nm wide, and 4 μm long, and patterned lines that are 33 nm wide. QC 20120618

Gold structures can be created in a scanning electron microscope (SEM) from the Me(2)Au(acac) precursor by direct writing with the electron beam. The as-deposited purity is usually poor, and a common purification approach is a post-annealing step that indeed is effective but also induces a volume reduction because of carbon loss and an undesirable reconfiguration of the gold structure, resulting in the loss of the original shape. We studied the shape change as a result of such purification, and to minimize this effect, the application of a tantalum and chromium buffer layer was investigated. These buffer materials are well-known for their good adhesion properties. We confirm by dedicated SEM, atomic force microscopy (AFM), and transmission electron microscopy (TEM) analysis that, for the creation of a uniform Au structure, tantalum is a better buffer layer material than chromium. Post-annealing of the Au electron-beam-induced deposition (EBID) patterns for 1 h at 600 °C in air resulted in a dramatic purity increase (from 8-12 atomic % Au to above 92 atomic % Au). The uncovered part of the tantalum layer can be easily etched away, resulting in a well-defined, high-purity, gold structure.

This indium-doped zinc oxide field effect transistor (IZO-FET) with a large ultraviolet (UV) detection sensitivity has been fabricated by inkjet printing technique. In darkness, the IZO-FETs exhibi ...

We have synthesized Mn-doped ZnO thin films by inkjet printing using a two-step annealing process at 200°C for the decomposition of the organic compounds, and at various temperatures above 400°C to tailor room temperature ferromagnetism. Highly c axis oriented 80 to 400 nm thin films on (001) Si substrates are obtained with a magnetic moment as large as 2.1?B/Mn2+. X-ray absorption and emission spectra measurements at the O K edge and the Mn L edge suggest strong p-d hybridization between the Mn2+ and O2-. Furthermore, Mn L edge XAS indicates the emergence of Mn3+/Mn4+ mixed valence states for films annealed above 500°C that leads to suppression of ferromagnetic ordering. All of these films show large and fast ultraviolet (UV) photoresponse with the decay times of about 0.5 ms, suggesting the potential for designing multifunctional UV sensors.

We report the manufacturing of thin zinc oxide films by reactive magnetron sputtering at room temperature, and examine their structural and optical properties. We show that the partial oxygen pressure in DC mode can have dramatic effect on absorption and refractive index (RI) of the films in a broad spectral range. In particular, the change of the oxygen pressure from 7% to 5% can lead to either conventional crystalline ZnO films having low absorption and characteristic descending dependence of RI from 2.4–2.7 RIU in the visible to 1.8–2 RIU in the near-infrared (1600 nm) range, or to untypical films, composed of ZnO nano-crystals embedded into amorphous matrix, exhibiting unexpectedly high absorption in the visible–infrared region and ascending dependence of RI with values varying from 1.5 RIU in the visible to 4 RIU in the IR (1600 nm), respectively. Untypical optical characteristics in the second case are explained by defects in ZnO structure arising due to under-oxidation of ZnO crystals. We also show that the observed defect-related film structure remains stable even after annealing of films under relatively high temperatures (30 min under 450 °C). We assume that both types of films can be of importance for photovoltaic (as contact or active layers, respectively), as well as for chemical or biological sensing, optoelectronics etc.

We report a systematic study of the thickness dependency of room temperature ferromagnetism in pristine MgO (~100-500 nm) and ZnO (~100-1000 nm) thin films deposited by reactive magnetron sputtering technique under the respective identical controlled optimum oxygen ambience. As far as we know this is the first such report on ferromagnetic pure MgO thin films, a result which should be of significance in understanding the functional aspects of magnetic tunnelling characteristics in devices using MgO dielectrics. From the magnetic characterization we observe a distinct variation in the saturation magnetization (MS) with increasing film thickness. In the case of MgO thin films MS values vary in the range 0.04-1.58 emu/g (i.e. 0.0012-0.046 ?B/unit cell) with increasing film thickness showing the highest MS value for the 170 nm thick film. Above this thickness MS is found to decrease and eventually above 420 nm the films show a paramagnetic behaviour followed by the well known diamagnetic property for the bulk (>500 nm). It is obvious that since initially the MS values increase with thickness, there has to be a maximum before the films become diamagnetic at some finite thickness. We also note that the MS values observed for MgO are the highest (more than twice the value observed for ZnO) to be reported for such a defect induced ferromagnetism in a pristine oxide. The origin of ferromagnetic order in both the oxides appears to arise from the respective cat-ion vacancies. The discovery of film thickness dependent ferromagnetic order should be very useful in developing multifunctional devices based on the technologically important materials MgO and ZnO.

Composite semiconductors provide routes for realizing high-performance electronic devices, but for many applications of such devices, low-cost manufacturing techniques are desirable. We have engine ...

Here, we report the design of a hybrid inorganic/organic mesoporous material through simultaneous pore engineering and hydrophobic surface modification of the intramesochannels to improve the uptake of superparamagnetic maghemite nanocrystals via impregnation techniques. The mesoporous material of the SBA-15 type was functionalized in situ with thiol organo-siloxane groups. Restricting the addition of the thiol organo-siloxane to 2 mol % yielded an inorganic/organic hybrid material characterized by large pores and a well-ordered hexagonal p6mm mesophase. The hydrophobic surface modification promoted the incorporation of 7.5 nm maghemite (gamma-Fe2O3) nanocrystals, prepared through temperature-controlled decomposition of iron pentacarbonyl in organic solvents. The hydrophobic, oleic acid capped superparamagnetic maghemite nanocrystals were incorporated into the porous network via wet impregnation from organic suspensions. Combining diffraction, microscopy, and adsorption data confirmed the uptake of the nanocrystals within the intramesochannels of the silica host. Magnetization dependencies on magnetic field at different temperatures show a constriction in the loop around the origin, which indicates immobilization of maghemite nanocrystals inside the thiol-functionalized silica host.

The physical and magnetic properties of magnetic nanoparticles are crucial for their effectiveness and reliability in biomedical applications. In this article, we report the synthesis of a stable H ...

We report a systematic study of nonlinearity in the ferromagnetic resonance of a series of submicron Permalloy ellipses with varying aspect ratios. At high excitation powers, the resonances are found to shift to higher or lower applied field. We focus here on the sign of the shift and its dependence on the applied field and shape-induced anisotropy of the ellipses. Using ferromagnetic resonance force microscopy, we find that the measured nonlinear coefficient changes sign as a function of anisotropy field and applied field in qualitative agreement with a macrospin analysis. This macrospin analysis also points to origins of the nonlinearity in a combination of hard-axis in-plane anisotropy and precession ellipticity. In comparison of the macrospin predictions with both experimental and micromagnetic modeling results, we measure/model values of the nonlinear coefficient that are more positive than predicted by the macrospin model. The results are useful in understanding nonlinear physics in nanomagnets and applications of spin-torque oscillators.

A ternary system of Mn0.5Zn0.5Fe2O4 has been synthesized for the first time using thermal decomposition of metal acetylacetonate in the presence of a high temperature boiling point solvent and fatty acids. Unlike the results of synthesis of this material by other techniques, we obtain nearly monodispersed nanoparticles, rendering them ideal for applications like in hyperthermia. The crystal structure and morphology of the particles obtained using x-ray diffraction (XRD) and transmission electron microscopy (TEM) are those of a single phase spinel structure with no other impurity phases. The particles are of 7 nm average diameter, with a very narrow (

LiNbO 3 /ZnO multi-layer with a preferred c-axis orientation has been grown on glass and SiO 2 /Si substrates by laser ablation technique. The piezoelectric activity in as deposited films is demonstrated using a novel approach to the atomic force microscope. In the presence of an in plane low frequency (0.1 to 5 Hz) ac electric field, we monitor and image the induced piezoelectric response normal to the film plane between two electrodes.

A LiNbO3/ZnO multilayer with a preferred c-axis orientation normal to the plane of the substrate was grown on glass and SiO2/Si substrates by laser ablation. The piezoelectric activity in as-deposited films was demonstrated using a novel approach to the atomic force microscope. In the presence of an in-plane, low-frequency (0.1–5 Hz) alternating current electric field, we monitored and imaged the induced piezoelectric response normal to the film plane between two electrodes.

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.

We report on the parametric excitation of magnetic precession modes in nanodisks using a parallel pumping configuration. The excitations are detected using a ferromagnetic resonance force microscopy method, and the parallel-pumped spectra reveal nonlinear characteristics including instability thresholds and multiple, narrow, sawtooth-shaped resonances. These characteristics are in accord with analytical theory and micromagnetic modeling results. Modeled mode profiles of the excitations show that higher-order standing spin-wave modes with both even and odd symmetries are excited under parallel pumping.

International audience; An oxygen-assisted electron-beam-induced deposition (EBID) process, in which an oxygen flow and the vapor phase of the precursor, tetraethyl orthosilicate (TEOS), are both mixed and delivered through a single needle, is described. The optical properties of the SiO(2+delta) (-0.04

We have fabricated by pulse laser deposition very thin (∼5-7 nm) and thick (∼27-408 nm) films of composition Fe66B24Nb4Ni6 on silicon and quartz substrates respectively, and studied their magnetic and magneto-optic properties at room temperature. We find that the thicker films on silicon can be tuned by appropriate thermal annealing to exploit soft magnetic characteristics with low HC, and high MS values. The magnetic hysteretic loops of the as-deposited thicker films on silicon substrates show two interesting characteristics: 1) increase in the coercivity with the film thickness and 2) the onset of a two stage process during the approach to magnetic saturation. The initial in-plane characteristic of the hysteresis loop is followed by a linear anisotropic behavior between remanence and saturation- that changes into square soft-magnetic loops on decreasing the film thickness. By suitable annealing the intrinsic strain disappears at relatively low temperatures (≤200 oC); the thicker films can be tailored to exhibit a simple soft-magnetic square loop with low HC. The ∼5-7 nm films deposited on glass are transparent and have been investigated for their magneto-optic properties using Faraday rotation (FR) measurement technique. Very high values of FR in the range 4-20 deg/µm almost linearly dependent on the wavelength of light in the range 405-611 nm are observed. The observed high values of Faraday rotation over a wide range of wavelength of light are useful for the applications as magneto-optic sensors in the UV to visible range.

We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

The atomic structure of ( La 1 - y Pr y ) 0.7 Ca 0.3 MnO 3 compound with 0.5≤ y ≤1 has been systematically studied by neutron powder diffraction in the temperature range from 15 to 293 K. For composition with y = 0.75, the structural analysis was performed on two samples, one containing the natural mixture of oxygen isotopes and the other one 75% enriched by 18 O. The room temperature structural characteristics of the series, including cell volume, average Mn-O bond distance, and average Mn-O-Mn bond angle, are the linear functions of the < r A >. Temperature dependencies of these parameters are quite smooth, except for the point T = T FM , where a jump like changes occur. The isotope enriched samples have been found identical in crystal and magnetic structure down to the temperature of transition of the sample with 16 O into the metallic ferromagnetic phase. It confirms that different transport and magnetic properties of the samples with 16 O and 18 O at low temperature are driven by the different oxygen atoms dynamics solely. Temperature dependencies of the CO and AFM diffraction peak intensities and of the peak widths for compositions close to the metal-insulator boundary ( y ≈ 0.75) indicate the macroscopically phase separated AFM-dielectric + FM-metallic state below T FM .

The effect of 16O→18O isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La0.35Pr0.35Ca0.3MnO3 epitaxial thin films deposited onto LaAlO3 and SrTiO3 substrates. For the films on LaAlO3, the isotope substitution resulted in the reversible transition from a metal-like to insulating state. The applied magnetic field ( H≥ 2T) transformed the sample with 18O back to the metallic state. The films on SrTiO3 remained metallic at low temperatures for both 16O and 18O, but the shift of the resistivity peak corresponding to onset of metallic state exceeded 63 K after 16O→18O substitution. The temperature dependence of both resistivity and magnetic susceptibility was characterized by hysteresis, especially pronounced in the case of the films on LaAlO3. Such a behavior gives certain indications of the phase separation characteristic of interplay between ferromagnetism and charge ordering.

The oxygen isotope effect has been studied in the Sm1-xCaxMnO3 system in the vicinity of a phase boundary at x = 0.85 and 0.88. Resistivity ?(T) and ac magnetic susceptibility ?'(T) measurements did not demonstrate any significant change in transport and magnetic properties of the system as a result of the 16O-18O isotope substitution, as opposed to the hole-doped manganites of the Ln1-xAxMnO3 system, where an enormous oxygen isotope effect has been reported.

Thin epitaxial films of (La1−xPrx)0.7Ca0.3MnO3 (x=0,0.25,0.5,0.75,1) were grown on (001) ZrO2(Y2O3) substrates by aerosol MOCVD at 750°C. The structure and electronic properties of the films were compared with those of the films on perovskite substrates and with ceramics of the same composition. The films on ZrO2(Y2O3) are (110) oriented and possess a varying in-plane orientation microstructure giving rise to an extremely high density of the large-angle boundaries (∼1011 cm−2). Above the maximum resistivity temperature Tp, the microstructure results in a ∼30 meV increase of the hopping energy of small polarons (∼130 meV) and suppression of the maximum of d ( log ρ/T)/ d (1/T) at the transition from Arrhenius like ( log ρ∝T −1 ) to Mott like ( log ρ∝T −1/4 ) temperature dependence of resistivity (ρ). Below Tp an empirical law log ρ=αT 2 + log ρ′ was derived indicating a thermally activated trapping of the itinerant charge carriers. Large-angle boundaries in the films on ZrO2(Y2O3) destabilize the ferromagnetic state and cause residual resistivity (ρ′) higher by a factor of 100 compared to the films on the perovskite substrates. They provide a reservoir for the tunnel magnetoresistance owing to the spin-polarized tunneling.

Magneto-optical properties were measured for (La1-x Prx )0.7 Ca0.3 MnO3 (x = 0, 0.25, 0.5, 0.75, 1) ceramic solid solutions, including temperature, magnetic field, oxygen isotope content and spectral dependences of the transverse Kerr effect (TKE). The TKE spectra after the transition to the ferromagnetic metallic state depend only weakly on the substitution of La for Pr as long as x 0.5. A surface magnetism contribution results in a TKE peak near TC but it can be suppressed by magnetic field or a long-time annealing. A significant oxygen isotope effect is observed for all compositions, being critical for x = 0.75. Hysteresis phenomena of two different types were observed in the temperature dependences of TKE. The first type, related to the ferromagnetic fluctuations, was found for x 0.5 (TKE is larger on cooling). The second type was related to the magnetically inhomogeneous state for x = 0.75 and 1 (TKE is larger on heating). The hysteretic variations in the magneto-optical spectrum of (La0.25 Pr0.75 )0.7 Ca0.3 MnO3 are referred to the possible charge carrier redistribution between the incipient ferromagnetic component and the charge ordered antiferromagnetic component.

The effect of the magnetic field H on the electrical resistivity ρ and magnetic moment M of (La0.25Pr0.75)0.7Ca0.3MnO3 ceramic samples with various concentrations of 16O and 18O isotopes is studied. The behavior of ρ(H) and M(H) is characterized by an unusual shifted hysteresis loop and slow relaxation at some of its sections. The effects observed are interpreted within the framework of a model that takes into account the coexistence of regions of a ferromagnetic metal and an antiferromagnetic insulator and their evolution in an external magnetic field.

A unique feature of incredibly large magnetoresistance and also the properties, in which electronlattice interactions play a key role, has attracted a lot of attention to manganese oxides. Oxygen isotope effect has proved to be spectacular in this system and it gives insight into many characteristics of interactions and charge transfer in this system. This review concentrates on transformation of properties induced by oxygen 16O–18O isotope substitution and mechanisms leading to this extraordinary effect.

The oxygen isotope effect on the magnetic structure and charge ordering in $({\mathrm{La}}_{0.25}{\mathrm{Pr}}_{0.75}{)}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ was studied by means of neutron powder diffraction. At first it was found that the two investigated samples, one containing the natural mixture of isotopes (99.7% ${}^{16}\mathrm{O}$, metallic at $Tl~100$ K), and the other one enriched by ${}^{18}\mathrm{O}$ in 75% (insulating in the whole temperature range), are identical at room temperature. At the temperature lowering the sample with ${}^{16}\mathrm{O}$ undergoes subsequent antiferromagnetic ${(T}_{\mathrm{AFM}}=150 \mathrm{K})$ and ferromagnetic ${(T}_{\mathrm{FM}}=110 \mathrm{K})$ transitions, while in the sample with ${}^{18}\mathrm{O}$ pure AFM ordering ${(T}_{\mathrm{AFM}}=150 \mathrm{K})$ is found. The temperature dependencies of the neutron diffraction peak intensities associated with charge ordering are also quite different in the samples with ${}^{16}\mathrm{O}$ and ${}^{18}\mathrm{O}$ and correlate with the behavior of the electrical resistivity and the magnetic structure. The temperature behavior of the intensities of the CO and AFM peaks may indicate the presence of phase segregation of the sample with O-16 onto AFM-insulating and FM-metallic phases at low temperature, though no indications of a macroscopic phase segregation were found.

Unique sensitivity of electrical resistivity to the 16O→18O isotope exchange was observed for (La1−yPry)0.7Ca0.3MnO3 ceramics and epitaxial thin films. At y=0.7, substitution of 16O by 18O in ceramic samples results in the reversible transition from a metal-like to insulating state. In thin films, this metal–insulator transition occurs at y=0.5 due to the strains induced by substrate. The applied magnetic field (H≥2 T) transforms the sample with 18O back to the metallic state. In such magnetic fields the temperature dependence of resistivity exhibits a peak corresponding to the onset of metallic state. The shift of the peak toward low temperatures after the 16O→18O exchange exceeds 50 K at 3 T for both ceramic and thin film samples. The results are interpreted in terms of the isotope dependence of the effective electron bandwidth which shifts the balance between the charge ordered insulating and the ferromagnetic metal-like states.

The effect of oxygen isotope substitution on the alternating-current magnetic susceptibility for (La1-yPry)0.7Ca0.3MnO3 ceramics (y = 0, 0.25, 0.5, 0.75, 1) was studied in the temperature range 4.2-300 K. At y < 0.75, the low-temperature behaviour of these manganites is typical for a ferromagnetic metal, whereas at y close to 1, the system behaves as an antiferromagnetic charge-ordered insulator. The 16O18O isotope substitution significantly shifts the Curie point TC, but has a smaller effect on the Neel temperature TN. At the crossover concentration y = 0.75, the exchange of 16O with 18O gives rise to a metal-insulator transition. The temperature dependence of the magnetic susceptibility is characterized by a pronounced hysteresis at y0 or 1, and the width of the hysteresis loops is strongly affected by the 16O18O exchange. The behaviour of the susceptibility in the paramagnetic phase gives an indication of the phase separation over quite a wide temperature range near the transition point. The phase diagram in the T-y plane is obtained and its modification with isotope substitution is discussed.

The evolution of the structural and magnetic properties of the CMR (colossal-magnetoresistance) compound La0.35Pr0.35Ca0.30MnO3 as the temperature changes from 10 to 293 K is investigated by means of neutron diffraction. It is shown that the changes in the transport and magnetic properties are directly related with the rearrangement of the atomic structure. A phase transition to the metallic state occurs together with simultaneous ferromagnetic ordering of the manganese moments and is accompanied by a jump in volume. The static distortions of the oxygen octahedra which are observed to occur prior to the magnetic phase transition and which are practically absent at room temperature and in the FM phase attest to the orbital ordering of oxygen atoms on the bonds, with freezing-in of the Jahn-Teller modes.

Single source MOCVD techniques were used to prepare perovskite films with metallic conductivity (CaRuO3, LaΝiO 3 , La0.5Sr0.5CoO3 and (La, Pr)0.7(Sr, Ca)0.3MnO3). Structural and electrical properties of the epitaxial layers on the coherent substrates are close to that of the films grown by pulsed laser deposition and magnetron sputtering. Peculiarities of the growth occur on the worse matched substrates, such as a mixture of two orientations, each aligned in the plane of the interface (LaΝiO3/ΜgO) and variant structures in the films on yttrium stabilized zirconia. X-ray diffraction of the films indicates pseudocubic lattice for all R1xx ΑxΜO3 films in spite of the distortions in the bulk material. The dependence of metal-insulator transition in R1-xΑx ΜnO 3 on the nature of R and Α and film-substrate lattice mismatch was studied.