High Quality La0 Research Articles

Optimization of temperature coefficient of resistivity and magnetoresistance of La0.67Ca0.33Mn0.98Fe0.02O3: Agx ceramics by Ag adjustment

High-quality La0.67Ca0.33Mn0.98Fe0.02O3: Agx ceramics were prepared by sol-gel and solid-phase methods. Ag and Ag+ were found to be present in the system after Ag doping, exhibiting a significant effect on the crystal structure and the concentration of Mn3+/Mn4+. Ag provided the desired conductive pathway, promoted the connectivity between grains, and improved the electrical conductivity of the ceramic. With the increase of Ag doping, the resistivity gradually decreased, while the Curie and the metal-insulator transition temperatures gradually increased. The temperature coefficient of resistivity (TCR) and the magnetoresistance (MR) were greatly improved. At x = 0.15, the peak TCR reached 75.4%·K−1, and the peak MR reached 87.0%. In order to adjust the TCR and MR, the contents of Ag and Ag+ were optimized by controlling the amount of Ag doping. The results demonstrated that Ag doping can regulate the metal-insulator transition and ferromagnetic-paramagnetic transition of the system effectively.

Improvement of electrical and magnetic properties in La0.67Ca0.33Mn0.97Co0.03O3 ceramic by Ag doping

For the perovskite manganite La1-xCaxMnO3, achieving high temperature coefficient of resistance (TCR) and magnetoresistance (MR) is the key to realize its potential applications. In this study, high-quality La0.67Ca0.33Mn0.97Co0.03O3:Agx polycrystalline ceramics were prepared by the sol-gel method. The results show that Ag doping has important impact on metal-insulator and ferromagnetic-paramagnetic transitions. A Ag doping amount increases, the grain size of the samples increases at x = 0.05 and then decreases. The doping of Ag can improve the crystalline quality of the samples and enhance the connectivity between grains, thereby improving the metallicity of the system. Additionally, with Ag doping amount increases, the resistivity of the samples gradually decreased, while the Curie temperature and the metal-insulator transition temperature gradually increased. Especially after Ag doping, both the TCR peak (TCRpeak) and the MR peak (MRpeak) values are significantly improved. The TCRpeak reaches 65.2%·K−1 at x = 0.1, while the MRpeak is as high as 82.6% at x = 0.05 under 1 T magnetic field. Doping perovskite manganite ceramics with Co and Ag can greatly optimize their TCR and MR, favoring the potential applications of these materials.

Nanoscale structural characterization of manganite thin films integrated to silicon correlated with their magnetic and electric properties

A detailed nanoscale structural characterization was performed on high-quality La0.66Sr0.33MnO3 (LSMO) thin films of different thicknesses and deposited by pulsed laser deposition onto buffered Si (100) substrates. A multilayered structure built of Y0.13Zr0.87O2 (YSZ) and CeO2 layers was used as buffer in order to optimize the manganite films growth. The stacking of the different layers, their morpholohy, composition and strains were analysed using different experimental techniques. In-situ characterization of the films, performed with reflection high-energy electron diffraction, revealed their epitaxial growth and smooth surfaces. High-resolution transmission electron microscopy (HR-TEM) images showed sharp interfaces between the constituents lattices and combined with energy-dispersive X-ray analysis allowed us to determine that there was no ion interdifussion across them. The Fourier-Fast-Transform of the HR-TEM images was used to resolve the epitaxy relationship between the layers, resulting in [100] LSMO (001) ‖ [110] CeO2 (001) ‖ [110] YSZ (001) ‖ [110] Si (001). The LSMO thin films were found to be ferromagnetic and metallic at low temperature regardless their thickness. The effect of strains and defects was only detected in films thinner than 15 nm and put in evidence by X-ray diffraction patterns and correlated with magnetic and electrical parameters.

Preparation of High-Quality Conductive La0.7Sr0.3MnO3 Buffer Layer Applied to Low-Cost YBCO-Coated Conductors

Through a simple and low-cost way to gain the precursor solution, a conductive and high-quality La0.7Sr0.3MnO3 (LSMO) buffer layer approximately 280 nm thick only by one single coating was successfully deposited on LaAlO3 (LAO) (100) single crystal substrates using an independently developed new method of polymer-assisted chemical solution deposition (PA-CSD). Highly epitaxial YBa2Cu3O7−x (YBCO) superconducting film with thickness of 500 nm managed to be deposited on LSMO/LAO. A study was made on the LSMO buffers and YBCO films with XRD, SEM, and superconducting critical temperature (Tc) analyses. The temperature-dependent resistivities of YBCO on insulating BaZrO3 (BZO) buffer layer and on conductive LSMO buffer layer were also investigated. It was found that the conductive LSMO buffer prepared at 840 °C in argon would possess high-degree out-of-plane and in-plane texturing, good density with a sufficient thickness about 280 nm, and microcrack-free nature. More importantly, the value of the self-field critical current density (Jc) of YBCO superconducting film on LSMO/LAO architecture was 2.8 MA/cm2 at 77 K.

Superparamagnetic state in La0.7Sr0.3MnO3 thin films obtained by rf-sputtering

A novel superparamagnetic state has been observed in high quality La0.7Sr0.3MnO3 (LSMO) thin films directly grown by rf-sputtering on SiOx/Si(100) substrates. The films are nanostructured without grain boundaries, constituted by locally epitaxial nanoregions grown layer-by-layer with out-of-plane (012) preferential orientation, induced by the constrain of the native silicon oxide. Low magnetic field ZFC-FC magnetization curves show a cross-over from superparamagnetic to ferromagnetic state dependent of the thickness. The thicker film (140 nm) exhibits typical ferromagnetic order. The thinner films (40 and 60 nm) exhibit superparamagnetic behavior attributed to interacting ferromagnetic monodomain nanoregions with critical size, random in-plane oriented, where the inter-monodomain boundaries with surface spin-glass structure regulate the blocking of magnetization depending on the magnetic field intensity. M(H) hysteresis loops showed noticeable coercive fields in all samples, larger than those reported for LSMO. Such properties of half-metal LSMO film foresee potential integration in new Si-technology nanodevices in Spintronics.

Large increase of Curie temperature in (110)-oriented La0.7Sr0.3MnO3 films

From the perspectives of scientific researches and practical applications, it is desirable to explore high operating temperature ferromagnetic films. The effect of biaxial strain on magnetic properties of (110)-oriented La0.7Sr0.3MnO3 films was studied. High quality La0.7Sr0.3MnO3 films were grown on (110)-oriented perovskite single crystal substrates using pulsed laser deposition, varying substrate-induced misfit strains from − 2.27–0.75%. A remarkable enhancement of Curie temperature has been achieved for (110)-oriented La0.7Sr0.3MnO3 films clamped with small misfit strains (i.e., grown on LAST (110)). The enhanced Curie temperature of (110)-oriented La0.7Sr0.3MnO3 films could be attributed to the misfit strain between the films and the underlying substrates and may have technological implication for applications at high temperature environments.

Antiferroelectric single crystal of La0.011Pb0.984(Lu1/2Nb1/2)O3 with high energy storage density

High quality La0.011Pb0.984(Lu1/2Nb1/2)O3 (La-PLN) antiferroelectric (AFE) single crystal was successfully obtained by a top-seed solution growth technique. The crystal structure adopts an orthorhombic phase and two sets of superlattice reflections due to B-site ordering and anti-parallel cation displacement are observed clearly and distinguished by the X-ray diffraction patterns (XRD). The Curie temperature TC is near 221°C with a low dielectric constant (about 371). The energy storage density decreases along with the temperature increasing and the maximum energy storage density is up to 5.03J/cm3 at 25°C. The results indicate that the La-PLN single crystal is a promising candidate for the AFE energy storage application.

Short-range ferromagnetic order in perovskite manganite La0.62Er0.05Ba0.33Mn0.95Fe0.05O3

The critical phenomena of a high quality La0.62Er0.05Ba0.33Mn0.95Fe0.05O3 sample are comprehensively studied using dc magnetometry in the vicinity of paramagnetic to ferromagnetic second order phase transition. The critical exponents are estimated through various techniques such as Modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. In comparison with the values given by standard models, the critical exponents β, γ and δ in our case are close to those expected from the three-dimensional Ising model (β = 0.322 ± 0.004, γ = 1.175 ± 0.002 and δ = 4.415 ± 0.02 at an average TC = 256.53±0.06 K). This proves the existence of a short-range ferromagnetic order in La0.62Er0.05Ba0.33Mn0.95Fe0.05O3. Thus, the scaling law γ + β = δβ is fulfilled. With these critical exponents, the isothermal magnetization data around TC fall into two branches of a universal function M(H, ε) = |ε|β f±(H/|ε|β+γ) where ε = (T−TC)/TC is the reduced temperature.

Short-range ferromagnetic order in La0.67Sr0.16Ca0.17MnO3 perovskite manganite

The critical phenomena of a high quality La0.67Sr0.16Ca0.17MnO3 sample are comprehensively studied using dc magnetometry in the vicinity of paramagnetic to ferromagnetic second order phase transition. The critical exponents are estimated by various techniques such as the Modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. In comparison with the values given by standard models, the critical exponents β, γ and δ in our case are close to those expected from the three-dimensional Ising model (β=0.324±0.005, γ=1.176±0.03, and δ=4.724±0.03 at an average TC=333.18±0.2K). This proves the existence of a short-range ferromagnetic order in La0.67Sr0.16Ca0.17MnO3. Thus, the scaling law γ+β=δβ is fulfilled. With these critical exponents, the isothermal magnetization data around TC fall into two branches of a universal function M(H,ε)=|ε|βf±(H/|ε|β+γ) where ε=(T-TC)/TC is the reduced temperature.

Low temperature electrical transport behavior of La0.7Ba0.3MnO3 thin Films on LaAlO3 substrates

The high-quality La0.7Ba0.3MnO3 (LBMO) epitaxial films were deposited on (001) oriented LaAlO3 (LAO) substrates by magnetron sputtering technique. The low temperature electrical transport behavior of the films was investigated in details. In the low temperature ferromagnetic metallic state, a common feature, i.e., the minimum of electrical resistivity, was found in both of the films post annealed in oxygen and argon atmosphere. By taking the unusual combination of factors including spin dependent Kondo-like scattering, electron–electron and electron–phonon interactions into account, the resistivity minimum can be fitted well. It was found that the spin dependent Kondo-like scattering plays an important role in both the films, indicating the intrinsic spin disorder in strongly correlated manganites. Furthermore, in a lower temperature interval 4–25K, a stronger electron–electron interaction was observed in the Ar annealed films, which can be attributed to the enhanced disorder arising from oxygen vacancy.

The Fabrication of La<sub>0.9</sub>Sr<sub>0.1</sub>CoO<sub>3</sub> Thin Films and its LITV Effect Applications

High quality La0.9Sr0.1CoO3 (LSCO) thin films grown on 5° vicinal cut LaAlO3 (LAO) (100) substrates were deposited by pulse laser deposition (PLD). Laser induced thermoelectric voltage (LITV) was detected instantly with fast response time and extremely narrow full width at half maximum (FWHM) when 248 nm pulse laser radiated on the surface of LSCO thin films. These merits of LSCO thin films make it one ideal material to fabricate light detectors and photosensitive device. With the increase of pulse laser energy, the peak voltages increase linearly, so LSCO thin films can be used to make high precision laser energy/power meter.

The size effect on transport properties of colossal magnetoresistance materials La0.67Ca0.33MnO3

High quality La0.67Ca0.33MnO3 (LCMO) film was deposited via a novel pulsed electron deposition technique on SrTiO3(100) single crystal substrate. The micro-bridge with different widths was fabricated by using electron beam lithography (EBL) technique and their transport properties were studied. For the micro-bridges with width of 2 and 1.5 μm, the insulator-to-metal transition temperature (T P) keeps unchanged compared with the film. For the micro-bridges with width of 1 μm, the T P shifts towards the lower temperature by 50 K. When the width decreases down to 500 nm, the insulator-to-metal transition disappears. The magnetoresistance behavior of these micro-bridges was studied, and the results show that the low field magnetoresistance (LFMR) decreases and the high field magnetoresistances (HFMR) keep almost unchanged as the width of micro-bridge is reduced.

Preparation of PZT thin films on conductive perovskite LSCO electrodes films by pulsed laser deposition

High quality La0.5Sr0.5CoO3 (LSCO) thin films have been prepared by pulsed laser deposition(PLD). The target was prepared by using citrate processing method. The electrical resistivity versus temperature has been measured. The LSCO thin films were grown epitaxially on LaAlO3(100) substrates, whereas the LSCO films on Si(100) or Si(111) show to be polycrystalline. The resistivity of the films is slightly larger than that of the targets. The PZT films were grown on LSCO/LAO(100) substrates forming heterostructures and their ferroelectric hysterisis has been measured

Growth of colossal magnetoresistance thin films on silicon

We are able to grow high quality La0.67Sr0.33MnO3(LSMO) colossal magnetoresistive (CMR) thin films on Y-stabilized zirconia (YSZ) buffered (100) Si substrates using a Bi4Ti3O12 texturing and lattice matching layer. The CMR films have very high structural perfection and show excellent transport and ferromagnetic properties, including the almost full saturation magnetization values and narrow ferromagnetic resonance peaks (15 Oe at 290 K). The lattice matching template/buffer layer approach is suitable for the high quality CMR films on Si. A close correlation between the magnetic hysteresis loop and the field dependence of MR is observed at lower temperatures.

Epitaxial La0.5Sr0.5CoO3 electrode films for ferroelectric device applications

Abstract We have grown high quality La0.5Sr0.5CoO3 thin films by Pulsed Laser Deposition. This material is a electrically conducting perovskite which can be used as structurally compatible electrodes for devices using ferroelectric materials such as Pb-La-Zr-Ti-O (PLZT). Oxygen stability was investigated under various annealing conditions. LSCO/PLZT/LSCO heterostructures were grown epitaxially on SrTiO3 (STO) and MgO substrates. P-E hysteresis loop was observed with Pr = 20 μC/cm2 and Ec = 24 kV/cm. Direct observation of the piezoelectric effect in PLZT was made by measuring the PLZT c-axis lattice constant under various electric fields. LSCO/STO superlattice was also grown by PLD. The superlattice showed excellent crystallinity with a Rutherford Backscattering (RBS) channeling minimum yield of only 3.6%.