MnO3 Manganite Films Research Articles

Surface Mode in a Spin-Wave Resonance Spectrum of La0.67Ca0.33MnO3 Manganite Film with Elastic Deformation

The spin-wave resonance spectrum is a characteristic of a magnetic film. The surface mode of this spectrum depends on the magnitude and nature of the stress state of the surface layer of the film. Parameters of this mode are independent on the film conductivity.

Accelerated ageing effects in nanostructured La0.83Sr0.17MnO3 films

The kinetics of resistivity and magnetoresistance change was studied during ageing of thin nanostructured La0.83Sr0.17MnO3 manganite films grown on lucalox (99.9% Al2O3+0.01% MgO) substrate by PI MOCVD method. It was obtained that accelerated ageing of the films in Ar atmosphere at temperatures of 100–200°C as well as long-term ageing during two years at room temperature leads to the significant increase of film resistivity, but has a negligible influence on the magnetoresistance of the film in magnetic fields higher than 1T. It was found that the accelerated ageing decreases demagnetization field of thin films and, as a result, the magnetoresistance anisotropy is decreased at low field region. The obtained results are analyzed using typical for topologically-disordered systems model of hierarchically limited relaxation dynamics described by stretched exponent. The analysis of resistivity vs. temperature dependence in paramagnetic state by using Mott's variable range hopping model showed that localization length of charge carriers decreases during annealing or long-term ageing processes. The possible reasons of observed changes are explained by oxygen diffusion and its depletion in the grain boundaries of the films. The possibility to accelerate ageing process of nanostructured manganite films and to achieve higher stability of magneto-resistive sensors based on these films is discussed.

Role of strain and microstructure in chemical solution deposited La0.7Pb0.3MnO3 manganite films: Thickness dependent swift heavy ions irradiation studies

Owing to the higher magnetic transition temperature (TC), above RT and large magnetoresistance (MR) exhibited by La0.7Pb0.3MnO3 (LPMO) manganite, we have carried out the studies on the effect of 200MeV Ag+15 ion irradiation on LPMO films. It is interesting to note that, the modifications in the surface grain morphology and roughness in higher thickness (>200nm) LPMO films, due to irradiation, affects the transport and magnetotransport, in a prominent manner, which has been understood in the light of enhancement in the scattering of charge carriers. The results of the structural, microstructural, transport and magnetotransport properties of pristine and irradiated LPMO films (150–350nm) have been discussed in this communication.

Sign Reversal of Junction Magnetoresistance in p-La0.7Ca0.3MnO3/SiO2/n-Si Heterostructure: A Possibility in Spintronics Application

We have fabricated a p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure, consisting of a p-type manganite (La0.7Ca0.3MnO3) and n-type Si with a interfacial layer of SiO2 with typical thickness of about 9 nm using pulsed laser deposition technique. The junction exhibits rectifying behavior over the temperature range of 10-300 K with rectification factor 52 at room temperature. Investigation on the electrical properties of p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure exhibits nonlinear J-V characteristics in a wide temperature range. A crossover from negative to positive junction magnetoresistance (JMR) is observed in p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure in current perpendicular to film plane (CPP) geometry. The temperature dependent sign of junction magnetoresistance of the heterojunction has been investigated carefully in details. It is found that the junction exhibits the positive junction magnetoresistance when the temperature is greater than the ferromagnetic to paramagnetic transition temperature (Tc) of the top highly spin-polarized half-metallic ferromagnetic La0.7Ca0.3MnO3 manganite film layer. The relation between junction magnetoresistance and external magnetic field is found to be of (delta rho/rho approximately equal alphaHbeta) type having both alpha and beta temperature dependent. We attribute the emergence of negative JMR at lower temperature (< Tc) and positive JMR at higher temperature (> Tc) to the quantum mechanical tunneling transport mechanism across the heterojunction. Our results might be very useful to fabricate artificial devices using the manganite-based heterojunction grown on single crystalline n-Si (100) in spintronics device applications.

Effect of lateral tensile stresses on the low-temperature electrical resistivity and magnetoresistance of La0.67Ca0.33MnO3 nanofilms

The thickness of the buffer layer of strontium titanate introduced between an La0.67Ca0.33MnO3 manganite film and a (001)La0.29Sr0.71Al0.65Ta0.35O3 substrate is varied (d1 = 7–70 nm) to influence effective misfit m in their lattice parameters. As m increases, electrical resistivity ρ of the film increases sharply and the maximum in the ρ(T) dependence shifts toward low temperatures. At T < 150 K, the temperature dependence of ρ of the manganite film obeys the relationship ρ = ρ1 + ρ2T4.5, where parameter ρ1 is independent of the temperature and magnetic field. Coefficient ρ2 decreases with increasing magnetic field and increases with the misfit between the lattice parameters of the film and substrate, i.e., when the effective hole concentration in the manganite layer decreases.

Magnetization reversal of thin La0.7Sr0.3MnO3 manganite films grown on LaAlO3

The kinetics of magnetization reversal and the dynamics of domain walls in thin La0.7Sr0.3MnO3 manganite films grown on a LaAlO3 substrate are studied. The micro-domains with out-of-plane spontaneous magnetization are shown to be metastable. These domains are replaced by wide macro-domains with an in-plane spontaneous magnetization after saturation by both out-of-plane and in-plane magnetic fields. The subsequent magnetization reversal is found to occur via the nucleation and thermoactivated motion of the 180° domain walls, the dynamic parameters of which have been determined.

Kinetics of magnetization reversal in a thin La0.7Sr0.3MnO3 manganite film

The kinetics of magnetization reversal of a thin LSMO film has been studied for the first time. It is shown that the magnetic domain structure critically depends on the conditions of structure formation. In the demagnetized state (after zero-field cooling from T c ), a maze-like domain microstructure with perpendicular magnetization is formed in the film. However, after field cooling and/or saturating magnetization by a field of arbitrary orientation, the [110] direction of spontaneous magnetization in the film plane is stabilized; this pattern corresponds to macrodomains with in-plane magnetization. Further film magnetization reversal (both quasi-static and pulsed) from this state is implemented via nucleation and motion of 180° “head-to-head” domain walls. Upon pulse magnetization reversal, the walls “jump” at a distance proportional to the applied field strength and then undergo thermally activated drift. All dynamic characterisitcs critically depend on the temperature when the latter varies around the room temperature.

Synthesis and Magnetic Properties of Pr&lt;sub&gt;0.7&lt;/sub&gt;Ca&lt;sub&gt;0.3&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; Manganite Films

Data on the magnetic properties of polycrystalline Pr0.7Ca0.3MnO3 manganite films obtained for the first time by extraction pyrolysis are presented. The effect of synthesis temperature on the magnetic properties of the manganite films is shown.

Magnetic properties of La0.7Sr0.3MnO3 manganite films obtained by extraction pyrolysis

The structural and magnetic properties of manganite films obtained for the first time by extraction pyrolysis have been experimentally investigated. It has been established that at annealing temperatures T ≈ 600 K the films are fine-grained and have spin-glass-like magnetic properties. Prolonged annealing at T ≥ 700 K results in grain overgrowth and ferromagnetic behavior.

Features of the magnetic properties of La0.7Sr0.3MnO3 Manganite films obtained by an extraction-pyrolysis method

We have experimentally studied the magnetic properties of manganite films obtained for first time using an extraction-pyrolysis technique. It is established that the characteristics of samples significantly depend on the conditions of final annealing. The annealing at temperatures Ta < 970 K is accompanied by strong thermomagnetic effects, and the resulting films possess properties similar to those of spin glasses. When the annealing temperature is increased to Ta ≥ 1020 K, the films exhibit magnetic properties typical of ferromagnetic systems.

Linear deformation effect on the SWR acoustic mode in La0.67Ca0.33MnO3 manganite film

AbstractIn this work, the influence of linear deformation on the magnetic resonance spectrum including the surface spin wave mode in La0.67Ca0.33MnO3 manganite film grown on LiNbO3 substrate has been investigated using a microwave technique. The parameters of the spectrum are established to depend strongly on strains in the film that influence both the profile of the magnetic resonance spectrum and the mode position and intensity. The magnetostriction constants of both the bulk film and surface mode were first determined using the shift of resonance fields as a function of mechanical stress. The tensile strain is shown to favor excitation of the surface spin‐wave mode, and its influence is stronger on the film surface layer. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Local structure and electronic properties in colossally magnetoresistive thin film of La0.87Na0.13MnO3 by Mn-K edge EXAFS and XANES

Mn-K edge EXAFS and XANES spectra of La0.87Na0.13MnO3 manganite films with different thicknesses (750, 250, 125 and 50Å), have been acquired at RT. In the 50Å film a shift of the Fermi level downward in energy is found if compared to the other films. In addition, the density of the empty minority spin states is decreased. This finding has been attributed to the presence of some Mn ions experiencing a different local chemical environment that results in the breaking of some DE paths, and in addition to an Anderson localisation of the charge carriers. This last conclusion can explain both the strongly insulating nature and the spin glass like behaviour of the magnetic response of the 50Å film, and has been corroborated by the results of the EXAFS analysis.

Structural and magnetic properties of ultrathin epitaxial La0.7Ca0.3MnO3 manganite films: Strain versus finite size effects

We present a structural and magnetic study of La0.7Ca0.3MnO3 epitaxial films (the thickness ranges from 2.4 to 80 nm) on SrTiO3. Their structure, as obtained by x-ray diffraction, is orthorhombic with a 45° rotated 2×2 square lattice, referred to the SrTiO3 substrate, in the film plane. The 2.4 nm film adopts a different structure as evidenced by the extinction of particular diffraction peaks and supported by the behavior of the size of the in-plane structural domains. While no important structural changes are detected for the other films as the layer thickness is reduced, Tc decreases drastically while the remanent magnetization is constant. Tc follows the functional dependence of a mean field approximation for the limitation of the divergence of the spin–spin correlations by the film thickness.