La0.7Ba0.3MnO3 Research Articles

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.

Thickness Dependence Study of Electron Beam Evaporated LBMO Manganite Thin Films for Bolometer Applications

La0.7Ba0.3MnO3 (LBMO) thin films with different thicknesses were deposited on Si substrates using an electron beam evaporation technique for bolometer applications. To evaluate the influence of the thickness on their structural, compositional, morphological, and electrical properties, the LBMO thin films were characterized by x-ray diffraction (XRD), energy-dispersive spectroscopy, atomic force microscopy, and a four-probe method. XRD measurements showed that the crystal quality of the LBMO films improved with increasing thickness. The surface morphology revealed that the grain size and surface roughness of the films increased with increasing thickness. The resistivity increased with increasing thickness of the film. The temperature coefficient of resistance of the LBMO films decreased from 5.15%/K to 4.12%/K with increase of the film thickness from 20 nm to 100 nm.

Influence of substrate temperature on the electrical, morphological and structural properties of electron beam evaporated LBMO thin films

La0.7Ba0.3MnO3 (LBMO) thin films were deposited on Si substrates at various substrate temperatures (Ts) ranging from 823 K to 1023 K using electron beam evaporation (EBE), and studied the structural, composition and electrical properties of the films as a function of deposition temperature were studied. X-ray diffraction (XRD) studies revealed the epitaxial growth in the films. The surface morphology of the films were characterized by atomic force microscopy (AFM). The elemental composition analysis investigated by energy dispersive spectroscopy (EDS) confirmed the stoichiometry. The films deposited at higher substrate temperatures (1023 K), showed lower resistivity with a higher temperature coefficient of resistance (TCR). A TCR of 4.09%/K obtained in the present investigation is suitable for bolometric applications near to the room temperature.

Structure and magneto-transport parameters of partially relaxed and coherently grown La0.67Ba0.33MnO3 films

X-ray diffraction (XRD) and medium-energy ion scattering (MEIS) have been used to reveal distortions in the crystal lattice of La0.67Ba0.33MnO3 (LBMO) films formed in relaxation of mechanical stresses. The LBMO films 25 nm thick have been prepared by laser deposition. The XRD and MEIS data obtained suggest that biaxially and mechanically elastically stressed LBMO layers grow coherently on LSATO substrates, whose crystal lattice parameter differs only weakly from the corresponding LBMO parameter, whereas in the bulk of manganite films grown on LaAlO3 substrates, stresses relax partially. Stresses do not relax in the LBMO interface about 4 nm thick adjoining LaAlO3. The electro- and magneto-transport parameters of partially relaxed LBMO films have been compared with those obtained for coherently grown manganite films with approximately the same tetragonal distortion of the lattice cell (a (aSyen)/a (aEuro-) = 1.024-1.030; a (aEuro-) and a (aSyen) are the unit cell parameters in the substrate plane and normal to it, respectively). At temperatures substantially lower than the Curie temperature, the electrical resistivity rho of LBMO films fits the relation rho = rho(0) + rho(1) T (2) + rho(2)(H)T (4.5); the coefficients rho(0) and rho(1) do not depend on temperature T and magnetic field, and rho(2) does not depend on temperature but almost linearly decreases with increasing magnetic field strength H. The coefficient rho(2) for partially relaxed LBMO films is substantially larger than that for coherently grown manganite layers.

Magnetocrystalline anisotropy and spin-wave stiffness in tensile-strained La0.67Ba0.33MnO3 films: An investigation via ferromagnetic resonance

Tensile-strained epitaxial La0.67Ba0.33MnO3 (LBMO) film has been prepared by magnetron sputtering technique on (001) oriented spinel MgAl2O4 substrate. The transport and magnetic measurements give an insulator-metal transition and paramagnetic-ferromagnetic transition occurring at ∼150 K and 250 K respectively, which implies the phase separation in such a tensile-strained film. By analyzing the angular and temperature dependences of the ferromagnetic resonance (FMR), we determine the magnetocrystalline anisotropy of the film. It is found that the tensile-strained film is dominated by an easy-axis corresponding to the compressive out-of-plane direction, though the magnitudes of anisotropy constants are relatively small and their temperature dependences are some complex. Furthermore, the FMR spectra show additional spin wave resonance (SWR), and the field positions can be indexed to follow a linear dependence on the square of index n. The scaling gives a spin-wave exchange stiffness D of 20.7 meV Å2 at low temperature, which is less than half of that in strain-free LBMO films, implying that the double exchange interaction is remarkably suppressed in the tensile-strained LBMO films.

Effects of residual and tunable strain in thin films of La0.7Ba0.3MnO3

The effects of residual and tunable strain in thin films of La0.7Ba0.3MnO3 (LBMO) were investigated. Different residual strains were achieved by depositing LBMO films with various thicknesses on 0.7PbMg1/3Nb2/3O3–0.3PbTiO3 (PMN-PT) and SrTiO3 (STO). For LBMO on PMN-PT, when the thickness changes the resistance evolves dramatically. All samples on STO have a clear metal-to-insulator transition near room temperature. The tunable strain was modulated through the converse piezoelectric effects of PMN-PT. Clear voltage-controlled resistance modulations (|ΔR|/Rmax ∼ 90%) were observed in LBMO/PMN-PT. The magnitude and nonlinearity of elastoresistance are the largest in the thinnest sample. |ΔR|/R decreases as the thickness increases and is still substantial even the film is as thick as 150 nm. For thicker samples, the nonlinearity becomes weaker and the resistance changes linearly with voltage approximately.

Easy-plane magnetocrystalline anisotropy of compressive strained (La, Ba)MnO3 film

The magnetocrystalline anisotropy of La0.67Ba0.33MnO3 (LBMO) epitaxial films suffering large compressive strain on LaAlO3 (LAO) substrates (LBMO/LAO) was investigated by ferromagnetic resonance (FMR) in the temperature range between 2 and 320 K. By mapping out the dependence of the FMR position on the angle between the applied magnetic field and crystallographic axes of the films, a large easy-plane anisotropy has been found in such compressive strained LBMO films, which is in contrast to the general tendency presented in strained manganite films. Furthermore, the excellent epitaxial crystallographic orientation due to the LAO substrates gives rise to an appreciable fourfold symmetry of the in-plane anisotropy with easy-axis along the [110] direction. The results are discussed by taking tolerance factor and giant magnetostriction of Ba-doped manganites into account.

Improved crystallinity, spatial arrangement and monodispersity of submicron La0.7Ba0.3MnO3 powders: A citrate chelation approach

The perovskite manganite systems have been the materials of tremendous interest due to their strong correlation between structure, transport and magnetism. These materials in their single-crystal form show colossal magneto-resistance (CMR), but the applied fields are very high (∼1–5T). The polycrystalline samples do show high low-field magneto-resistance (LFMR), but good amount of control over particle sizes and grain-boundary distribution is required, which is well known but less realized in practical approaches. In this context, we report on synthesis and manipulation of polycrystalline La0.7Ba0.3MnO3 (LBMO) submicron powders using citric acid chelation. The Citrate-gel route is used to synthesize poly-dispersed LBMO powders which are subjected to citrate chelation for a duration of 0 (LB0) to 4h(LB4) . The samples show improved ordering in X-ray diffraction patterns. Raman spectroscopy scans indicate changed mode signatures due to the probable chelating process, which alters the surface morphology. X-ray photoelectron microscopy shows an evidence of fine citrate layer on the grain boundaries. Low temperature B–H curves exhibit fine hysteresis loops for all samples, while room temperature B–H curves shows paramagnetic response. Scanning electron microscopy images showed the formation of well arranged, connected, mono-dispersed grains of LB4 sample, as against polydispered LB0. The magneto-resistance (at H=100kOe) is seen to enhance for LB4 at its transition temperature (75%, as compared to LB0, where it is 60%), which can be attributed to the well-controlled inter-grain tunneling phenomenon and thin insulating regions in between, created due to citrate chelation, which probably enhances the scattering phenomenon and its susceptibility to applied fields. As citric acid is known to chelate Mn ions, it probably chelates the smaller LB particulate structure and leaves behind citrate-connected submicron grains of LBMO, which are seen to be well engineered.

Electro- and magnetotransport in La0.67Ba0.33MnO3 nanosized films coherently grown on a vicinally polished (LaAlO3)0.29 + (SrAl0.5Ta0.5O3)0.71 substrate

The structure, orientation, and the response of electroresistance to magnetic field H and varying temperature T have been studied for 30-nm-thick La0.67Ba0.33MnO3 (LBMO) films. The deviation of the [001] direction in manganite layers from the normal to the plane of the (LaAlO3)0.29 + (SrAl0.5Ta0.5O3)0.71 substrate strictly corresponds to the vicinal angle of the latter. The minimum yield determined from 227-keV proton scattering spectra is 0.025, signifying a high order of the cationic sublattice in the films. The biaxial compression of stable nuclei of the manganite phase affects their stoichiometry, thus contributing to the depletion of LBMO films in the alkaline-earth element. The maximum electroresistance values have been observed in the films grown at Tmax ≈ 320 K, a temperature about 20 K lower than the Curie temperature of the corresponding bulk single crystals, and the maximum magnetoresistance (MR ≈ −0.42, μ0H = 2 T) occurs at T ≈ 300 K. At low temperatures (T 0.5 T, the major current-carrier relaxation mechanism is the interaction with magnons.

Magnetocaloric Effect in La0.7Cd0.3MnO3, La0.7Ba0.3MnO3, and Nd0.7Sr0.3MnO3

We have based on isothermal magnetization curves to study the magnetocaloric effect (MCE) in fine-grained perovskite manganites of La0.7Cd0.3MnO3 (LCMO), La0.7Ba0.3MnO3 (LBMO), and Nd0.7Sr0.3MnO3 (NSMO) prepared by conventional solid-state reaction. Magnetic measurements were performed on a vibrating sample magnetometer, with a temperature increment of 1.0 K, and the applied field in the range of 0–1.8 T. Under an applied field of 1.8 T, the maximum magnetic-entropy change obtained for LCMO, LBMO, and NSMO taking place at their Curie temperature are about 2.3, 2.1, and 5.1 J/(kg⋅K), respectively. The large entropy change in NSMO makes it suitable for magnetic-cooling applications.

The investigation of reversible strain and polarization effect in (011)-La0.9Ba0.1MnO3 film using field effect configuration

We have investigated the influence of the electric bias field on the magnetic and transport properties of (011)-oriented La0.9Ba0.1MnO3 (LBMO) thin film epitaxially grown on (011)-0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) single crystal substrate. It was found that strain and polarization effects induced by electric bias coexist in the whole temperature range and both of them can modulate the transport properties of (011)-LBMO on PMN–PT. The relative change of resistance ΔR/R exhibits peak values of −22% and −32% for bias fields of +12 and −12 kV/cm, respectively, around metal-insulator transition temperature, TMI. However, the sign of ΔR/R shows polarity dependence at temperature far below TMI. Further careful analysis demonstrates that these two opposite behaviors can be ascribed to the different influence of strain and polarization effects on transport properties.

Strain Effects on the Electric and Magnetic Properties of the Magnetoresistive $\hbox{La}_{0.7}\hbox{Ba}_{0.3}\hbox{MnO}_{3}$ Films

We have synthesized (100) La0.7Ba0.3MnO3(LBMO) films on SrTiO3(STO), NdGaO3(NGO), LaAlO3(LAO), and MgO substrates using pulsed laser deposition and investigated their electric and magnetic properties. The structural, electric and magnetic properties of the LBMO films seemed to be dependent on lattice mismatch between LBMO and the substrate. The characteristics of the LBMO film on STO with negligible lattice mismatch were close to those of the bulk LBMO. Interestingly, the uniaxial-type stress acting on the LBMO film by the NGO substrate induced a distinctive difference in the magnetic hysteresis and the magnetoresistance curves measured for two orthogonal in-plane directions. A sudden drop of ~0.6% in the low field magnetoresistance curve of the LMBO on the NGO is probably related to spin dependent scattering of charge carriers going through magnetic domains or grains. On the other hand, the LAO and the MgO substrates with a large lattice mismatch of >5% did not effectively induced homogeneous lattice strain to the LBMO film.

Spin-polarized current effects in disordered La0.7Ba0.3MnO3 half-metal thin films

We have investigated by means of noise spectroscopy the transport properties of half-metal La0.7Ba0.3MnO3 (LBMO) thin films deposited on MgO substrates. A reduced metal–insulator transition temperature and a peculiar noise behaviour are observed in the films grown on MgO substrates, when compared with similar films grown on SrTiO3 substrates. In particular, a large increase in noise is observed below the metal–insulator transition temperature, associated with a current induced reduction in the excess noise level. This finding is explained in terms of the spin torque effect between regions with depressed Curie temperatures among the ferromagnetic metallic domains. The proposed theoretical model, taking into account the half-metal character of manganites, describes well the experimental data.

Fabrication of Single Crystalline (La,Ba)MnO3 Nanodot Array by Mo/SiOx Lift-Off Technique

Nanoimprint-lithography-based molybdenum lift-off was applied to fabricate a perovskite-type La0.8Ba0.2MnO3(LBMO) nanodot array on a SrTiO3(100) substrate in combination with an in situ pulsed laser deposition (PLD) technique. We fabricated a Mo/SiOx bilayer mask pattern to prevent the crystallization of the Mo layer even at 700 °C and successfully obtained a LBMO nanodot array with a dot size as small as 200 nm by removing the Mo layer using 0.1 N NaOH aqueous solution.

Quantifying interlayer exchange coupling via layer-resolved hysteresis loops in antiferromagnetically coupled manganite/nickelate superlattices

In superlattices made of a half metallic ferromagnet La2/3Ba1/3MnO3(LBMO) and a metallic paramagnet LaNiO3(LNO), the field dependence of the LBMO magnetization was studied using depth- and element-sensitive x-ray resonant magnetic scattering measurements. The superlattices have ten bilayers of LBMO and LNO, and the LBMO layers were antiferromagnetically coupled across LNO spacer layers. From the x-ray measurements, the magnetic hysteresis loop of each LBMO layer was obtained, and subsequently the obtained layer-resolved LBMO hysteresis loops were utilized to determine the interlayer exchange coupling.

Magnetoresistive Properties of Manganite-Based Heterojunctions

Hole-doped La2/3Ba1/3MnO3 (LBaMO), La2/3Ca1/3MnO3 (LCaMO) and La2/3Ce1/3MnO3 (LCeMO) thin films were grown heteroepitaxially on 0.1 wt.% Nb-doped SrTiO3(100) (STON) substrates by magnetron sputtering. The prepared LBaMO/STON, LCaMO/STON, LCeMO/STON heterostructures demonstrated nonlinear rectifying current–voltage characteristics. Negative magnetorestance values have been indicated at low bias, meanwhile bias-dependent magnetoresistance has been measured at positive bias voltage values U > Ud where Ud is the interfacial potential, corresponding to a steep current increase at a forward bias.

Low temperature growth of La0.67Ba0.33MnO3 thin films of high quality using pulsed laser deposition assisted by CO2 laser irradiation

La0.67Ba0.33MnO3 (LBMO) thin films of high quality were successfully fabricated at low temperature (400–450 °C) using pulsed laser deposition assisted by CO2 laser irradiation. It is shown that, at a low deposition temperature, LBMO thin films exhibit poor crystallinity and electrical and magnetic properties. With the aid of laser irradiation, LBMO thin films are significantly improved in their structure and quality and display a resistivity maximum of 6.3 mΩ cm at 304 K, a large magnetoresistance of 20% (at 300 K, H = 2 T) and a ferromagnetic Curie temperature of ∼320 K, which are close to those of the LBMO thin films deposited at 800 °C. The observed improvement in the properties of the LBMO thin films deposited at low temperature is inferred to be largely associated with the enhanced crystallinity of the film and a decrease in the oxygen deficiency due to laser irradiation.

Impact of Silver Addition on Room Temperature Magneto-Resistance in La0.7Ba0.3MnO3 (LBMO): Ag x (x=0.0, 0.1, 0.2, 0.3, 0.4)

La0.7Ba0.3MnO3 (LBMO): Ag x (x=0.0, 0.1, 0.2, 0.3, and 0.4) composites are synthesized by a solid-state reaction route, the final sintering temperatures are varied from 1300 °C (LBMO1300Ag) to 1400 °C (LBMO1400Ag), and their physical properties are compared as a function of temperature and Ag content. All samples are crystallized in single phase accompanied by some distortion in main structural phase peaks at higher angles with an increase in silver content. Though the lattice parameters (a,c) decrease, the b increases slightly with an increase in Ag content. The scanning electron micrographs (SEM) showed better grains morphology in terms of size and diffusion of grain boundaries with an increase in Ag content. In both LBMO1300Ag and LBMO1400Ag series, the metal insulator transition (T MI) and accompanied paramagnetic-ferromagnetic transition (T C) temperatures are decreased with an increase in Ag content. The sharpness of MI transition, defined by temperature coefficient of resistance (TCR), is improved for Ag added samples. At a particular content of Ag(0.3), the T MI and T C are tuned to 300 K and maximum magneto-resistance at 7 Tesla applied field (MR7 T) of up to 55% is achieved at this temperature, which is more than double to that as observed for pure samples of the both 1300 and 1400 °C series at same temperature. The MR7 T is further increased to above 60% for LBMOAg(0.4) samples, but is at 270 K. The MR7 T is measured at varying temperatures of 5, 100, 200, 300, and 400 K in varying fields from ±7 Tesla, which exhibits U and V type shapes. Summarily, the addition of Ag in LBMO improves significantly the morphology of the grains and results in better physical properties of the parent manganite system.

Epitaxial growth of colossal magnetoresistive films onto Si(100)

We report the growth of colossal magnetoresistive (CMR) films La0.7Ca0.3MnO3 (LCMO) and La0.9Ba0.1MnO3 (LBMO) onto Si (100) using a simple pulsed-laser deposition technique. To avoid oxidation of the Si surface, an initial growth of SrTiO3 of a few atomic layers was carried out. We found that epitaxial growth of LCMO and LBMO films on Si can be realized by optimizing the deposition process. The obtained LCMO and LBMO films show ferromagnetic nature and the resulted LCMO/Si and LBMO/Si heterojunctions exhibit good rectifying behavior with magnetically tunable characteristics.

Epitaxial Growth of La0.7Ba0.3MnO3 Thin Films on SrTiO3 and LaAlO3 Substrates by Metal-Organic Deposition

La0.7Ba0.3MnO3 (LBMO) thin films were successfully prepared on SrTiO3 (STO) and LaAlO3 (LAO) single-crystal substrates by metal-organic deposition (MOD). The microstructure and the crystallinity of the LBMO films were examined in detail by high-resolution transmission electron microscopy and electron diffraction. The lattice mismatch between LBMO and STO is small as -0.1%; thus, the LBMO films were found to be epitaxially well grown. However, on the LAO substrate, which has a lattice mismatch of ∼-3.2% with LBMO, the films exhibited interfacial misfit dislocations along the interface. For an IR sensor application, we calculated the temperature coefficient of resistance (TCR) from the R(T) measurements. The films grown on STO substrates exhibited a TCR of approximately 5%/K at 306 K compared with 7%/K at 253 K exhibited by the films grown on LAO substrates.