Behavior Of La0 Research Articles

Metastable magnetic behavior in La0.9Tb0.1MnO3

The linear and nonlinear magnetizations of La0.9Tb0.1MnO3 at low temperatures were reported in detail. The temperature dependence of magnetization shows peaks at 50, 100 and 150 K, respectively. When LaMnO3 is Tb-doped, its magnetic structure exhibits a canted antiparallel spin order. This is different from classical antiferromagnetic (AFM) in which the relaxation behavior takes place at about 150 K. At 50 K, Tb-doped LaMnO3 exhibits canonical spin glass behavior, arising from the competition of exchange and super-exchange between spins. The peak at 100 K shows neither spin glass behavior nor canted AFM behavior. Its peak value increases with frequency increasing, and the transition temperature of the peak shifts to higher temperatures with frequency increasing. The study of aging behavior at 100 K shows a periodical variable metastability, which is ascribed to the competition between ferromagnetic (FM)-, AFM- and sinusoidal-order interactions. This work should shed a light on understanding the complex magnetic structure of the perovskite oxides.

Critical behavior and spontaneous magnetization estimation in La0.5Sr0.5MnO3 compound

We report the critical behavior in La0.5Sr0.5MnO3 perovskite oxide manganite using methods including modified Arrott plot, Kouvel–Fisher plot, and critical isotherm analysis. By means of the above techniques around the ferromagnetic–paramagnetic (FM–PM) transition, the magnetic data analyzed shows the sample attending the second-order magnetic phase transition with the critical parameters β = 0.553±0.020 with TC=352.02±0.63K (from the spontaneous magnetization MS(T) below TC) and γ =1.169±0.058 with TC=352.49±0.85K (from the inverse initial susceptibility χ0−1(T) above TC). The exponent δ =3,216 independently obtained from the critical magnetization isotherm satisfies the Widom scaling relationδ=1+β/γ. Moreover, the critical exponents are in the theoretically expected values for mean-field interaction model rather than the other universal theory and also follow the single scaling equation of M(H,ε)ε−β=f±(H/εβ+γ). Furthermore, to estimate the spontaneous magnetization of La0.5Sr0.5MnO3 perovskite, we used the magnetic entropy change (−ΔSM), obtained from isothermal magnetization. The results of this approach are compared to results obtained from classical analysis using Arrott curves.

Unconventional switching behavior in La0.7Sr0.3MnO3/La0.7Sr0.3CoO3 exchange-spring bilayers

We report on the observation of exchange-spring behavior in complex oxide bilayers composed of high coercivity ferromagnetic (FM) La0.7Sr0.3CoO3 (LSCO) and low coercivity FM La0.7Sr0.3MnO3 (LSMO). The magnetization process from each individual layer is revealed by a combination of bulk magnetometry and x-ray magnetic circular dichroism measurements. The results show unexpected magnetic switching behavior which deviates from conventional exchange-spring systems in that reversible switching occurs not only within the soft LSMO layer but is also accompanied by the switching of an interfacial LSCO layer. The origin of such exchange coupling is discussed in terms of charge redistribution at the interface.

Interpretation of temperature-dependent thermoelectric power behaviour of La0.67Ba0.33MnO3 manganites

The temperature dependence of the thermoelectric power S(T) in polycrystalline La0.67Ba0.33MnO3 has been investigated. In the ferromagnetic regime, the phonon thermoelectric power is evaluated by incorporating the scattering of phonons with impurities, grain boundaries, charge carriers and phonon. The Mott expression is used to compute the electron diffusive thermoelectric power (Scdiff.) using Fermi energy as electron-free parameter. The Scdiff infers linear temperature dependence and Sphdrag increases exponentially with temperature, which is an artefact of various operating scattering mechanisms. The behaviour of the S(T) is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions in the La0.67Ba0.33MnO3. Numerical analysis of thermoelectric power of the present model shows similar results as those revealed from experiments.

Impact of Co doping on magnetic and electrical properties of La0.5Ca0.5Mn1−xCoxO3 (0≤x≤0.05) manganites

In this study, structural, magnetic and electrical properties of polycrystalline La0.5Ca0.5Mn1−xCoxO3 (x=0, 0.005, 0.0075, 0.01, 0.025 and 0.05) samples have been investigated using ac susceptibility, magnetization and resistivity measurements. Rietveld refinement of X-ray diffraction patterns indicates an orthorhombic structure with Pnma space group for all samples. No structural transition is observed due to Co doping. Magnetic studies show that the magnetization and real parts of ac susceptibility (χ′(T)) increase initially by increasing x up to x=0.025 and decrease by further increase in x, up to x=0.05. The notable point of this study is the ability of a 0.5% of Co doping to induce insulator–metal transition in the insulating undoped sample at low temperatures. Also, we report a feature of thermal hysteresis behavior in La0.5Ca0.5Mn1−xCoxO3 series, which is the inverted thermal hysteresis loop for 0.0075≤x≤0.05 samples. In the Co doping level range of 0≤x<0.0075, χ′(T) and resistivity (ρ(T)) curves show counterclockwise (CCW) and clockwise (CW) thermal hysteresis, respectively. On the other hand samples with 0.0075≤x<0.05 Co doping level exhibit CW thermal hysteresis in χ′(T) and CCW one in ρ(T) curves. The thermal hysteresis behavior is attributed to the interfacial elastic energy in the boundary among the phases with different magnetic states. Magnetic instability is reported for x=0 and 0.005 samples and possible reasons for these behaviors are discussed.

Ultrafast optical probes of dynamic behavior in La0.7Sr0.3MnO3/YBa2Cu3O7 − δ/La0.7Sr0.3MnO3 heterostructure

Ultrafast pump-optical probe spectroscopy was used to analyze carriers dynamics behavior in La0.7Sr0.3MnO3/YBa2Cu3O7 − δ/La0.7Sr0.3MnO3 heterostructure. Our results show the pump signal ΔR/R for higher laser power (such as 21 and 41 mW), below Tc, first goes positive, then crosses zero and goes negative, before relaxing back to equilibrium over a time scale of a few ten picoseconds. We extract the characteristic relaxation time of the different process by fitting the data at these powers with a three-exponential decay. For higher laser power, the long characteristic relaxation time are obtained, which implies the competition between FM order and SC order in the La0.7Sr0.3MnO3/YBa2Cu3O7 − δ/La0.7Sr0.3MnO3 heterostructure.

Tuning the dead-layer behavior of La0.67Sr0.33MnO3/SrTiO3 via interfacial engineering

Transition metal oxide hetero-structure has great potential for multifunctional devices. However, the degraded physical properties at interface, known as dead-layer behavior, present a main obstacle for device applications. Here we present the systematic study of the dead-layer behavior in La0.67Sr0.33MnO3 thin film grown on SrTiO3 substrate with ozone assisted molecular beam epitaxy. We found that the evolution of electric and magnetic properties as a function of thickness shows a remarkable resemblance to the phase diagram as a function of doping for bulk materials, providing compelling evidences of the hole depletion in near interface layers that causes dead-layer. Detailed electronic and surface structure studies indicate that the hole depletion is due to the intrinsic oxygen vacancy formation. Furthermore, we show that oxygen vacancies are partly caused by interfacial electric dipolar field, and thus by doping-engineering at the single-atomic-layer level, we demonstrate the dead-layer reduction in films with higher interfacial hole concentration.

Coexistence of considerable inter-particle interactions and spin-glass behavior in La0.7Ca0.3MnO3 nanoparticles

We have studied the magnetic and spin-glass (SG) properties of La0.7Ca0.3MnO3 single-crystalline nanoparticles, which were prepared by the mechanical milling method with different milling times (tm). Analyzing the susceptibility data in the paramagnetic region indicates both ferromagnetic (FM) and anti-FM interactions coexisting in nanoparticles. Additionally, there is a peak associated with the freezing temperature (Tf) appearing on the real part curve of the ac susceptibility, χ′(T). The Tf value increases with increasing frequency as expected for SG systems. The SG behavior was also checked by using the criterion parameter c = ΔTf/TfΔ(log10f), and the power law τ = τ0(T/Tg − 1)−zν. The obtained values of c ≈ 5 × 10−2, τ0 ≈ 10−5 s and zν ≈ 2–3 are consistent with those expected for SG-like systems, suggesting an existence of a SG phase transition at Tg below Tf, which decreases with decreasing ⟨D⟩. Basing on ln(f) versus Tf data, and the Néel-Arrhenius model [ln(f) = ln(f0) - Ea/kBT] and Vogel–Fulcher law [ln(f) = ln(f0) - Ea/kB(T - T0)], the Larmor frequency (f0), activation energy (Ea) and effective temperature (T0) for the samples with different ⟨D⟩ were determined. Obtained results indicate the existence a strong interaction between nanoparticles.

Rounding of a first-order magnetic phase transition in La0.7Ca0.3Mn0.85Ni0.15O3

We prepared a polycrystalline sample of orthorhombic La0.7Ca0.3Mn0.85Ni0.15O3, and then studied its critical behavior. Based on the Landau phase-transition theory and Banerjee's criteria, we have found the sample undergoing a second-order magnetic phase transition. This continuous transition is characterized by critical parameters of TC = 170 K, β = 0.320 ± 0.009, γ = 0.990 ± 0.082, and δ = 4.09 ± 0.17 determined from modified Arrott plots. With these values, the magnetization-field-temperature (M-H-T) behaviors of La0.7Ca0.3Mn0.85Ni0.15O3 below and above TC are well described by an equation of state M(H,ε)=εβf±(H/εβ+γ), where ε=(T−TC)/TC, f+ for T &amp;gt; TC and f− for T &amp;lt; TC. Having compared to the theoretical models, the critical-exponent values determined in our case are close to those expected for the 3D Ising model and mean-field theory. This indicates an existence of ferromagnetic short-range interactions in the system below TC. The nature of the transformation from first-order to second-order phase transitions related to the Ni doping is discussed in detail.

Modification of the La0.6Sr0.4CoO3 coating deposited on ferritic stainless steel by spray pyrolysis after oxidation in air at high temperature

The behaviour of La0.6Sr0.4CoO3 applied to ferritic stainless steel (AISI 430) by spray pyrolysis was investigated after oxidation at 800 °C in air. The film was characterized with regard to its morphology, structure and adhesion. The film was regular over the entire surface and adhered well to the metallic substrate. Oxidation modified the film structure, forming an oxide (SrCrO4) in the metal/coating region due to Sr diffusion from the coating and Cr diffusion from the metallic substrate. A thermodynamic computational simulation confirmed the formation and stability of this oxide.

Unconventional critical magnetic behavior in the Griffiths ferromagnet La0.4Ca0.6MnO2.8□0.2 oxide

Abstract The effects of oxygen vacancy on the critical magnetic behavior in La0.4Ca0.6MnO2.8□0.2 around the paramagnetic-ferromagnetic (PM-FM) phase transition were investigated through various techniques such as modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis via dc magnetization measurements recorded around the Curie temperature TC. The obtained critical exponents values are β∼0.8, γ∼0.7 and δ∼1.882 with TC∼164.5 K. Thus the scaling law γ+β=δβ is fulfilled. The critical exponents obey the single scaling-equation of state M ( H , e ) | e | − β = f ± ( H | e | − ( β + γ ) ) where, f+ for T>TC and f- for T>TC. The found exponents are inconsistent with any known universality class. These results attributed to the existence of Griffiths Phase (Triki et al. (2012) [1] ) seem to actually reflect the unconventional critical scaling of the magnetic susceptibility.

Anomalous magnetic behavior of La0.6Sr0.4MnO3 nano-tubes constituted with 3–12 nm particles

Uniform La0.6Sr0.4MnO3 (LSMO) nanotubes of an average diameter 180 nm were synthesized by a modified sol–gel method employing nanochannel porous anodic alumina templates. The nanotubes were characterized chemically and structurally by XRD, SEM, EDX, and TEM. Postannealed (700 °C for 1 h hour) nanotubes were found to be polycrystalline from XRD and SAED studies. To get further insight into the nanotube structure, HRTEM studies were done, which revealed that obtained LSMO nanotubes were structurally constituted with nanoparticles of 3–12 nm size. These constituent nanoparticles were randomly aligned and self-knitted to build the nanotube wall. Investigation of magnetic properties at this structured nanoscale revealed remarkable irreversibility between the zero field cooling (ZFC) and field cooling (FC) magnetization curves accompanied with a peak in the ZFC curve indicating spin-glass-like behavior. Structural defects and compositional variations at surfaces and grain-boundaries of constituent nanoparticles might be responsible for this anomalous magnetic behavior.

Synthesis, crystal stability, and electrical behaviors of La0.7Sr0.3Cr0.4Mn0.6O3−δ–XCu0.75Ni0.25 for its possible application as SOFC anode

La0.7Sr0.3Cr0.4Mn0.6O3−δ (perovskite-type) nanocomposites impregnated with XCu0.75Ni0.25 have been synthesized by sol–gel method. Crystal structure of LSCM–Cu0.75Ni0.25 composites were refined by the Rietveld method. Crystal symmetry of CuO and NiO nanoparticles have monoclinic $$ C12/c $$ and cubic $$ Fm\bar{3}m $$ symmetry, respectively, but after sintering at 1,200 °C and reducing the temperature to 600 °C, it’s transformed into a new Cu0.75Ni0.25 intermetallic solid solution without secondary phase. We have detected a cationic inter-diffusion in Cu ↔ Ni interphase crystals during this reduction process; however, when sintering time exceeds 2 h at 1,200 °C this reaction mechanism is interrupted by a sublimation phenomenon; which causes Cu2O cubic structure segregation from monoclinic CuO structure. This leads to Cu precipitation from the Cu1−x Ni x solid solution. Cu0.75Ni0.25 inhibits the LSCM perovskite-type grain growth (t ≈ 220 nm). Electrical conductivity indicates the presence of semiconductor and metallic-type behaviors with a maximum electrical conductivity (800 °C) >4.5 (log σ, Sm cm−1). When Cu0.75Ni0.25 concentration was 25 and 35 %, semiconductor behavior were dominated. Thermal expansion coefficients showed a linear dependence inversely proportional to Cu0.75Ni0.25 concentration. Electrical conductivity, Rietveld analysis, Porosity, TEC, and E a behaviors lead to the conclusion that the anodes between 25 and 35 % (Cu0.75Ni0.25) are closer to applications at SOFC.

Critical Behavior Near the Paramagnetic to Ferromagnetic Phase Transition Temperature in Polycrystalline La0.57Nd0.1Sr0.33Mn1−x Al x O3 (0.0≤x≤0.1)

The critical parameters provide important information concerning the interaction mechanisms near the paramagnetic to ferromagnetic transition. In this paper, we have investigated the effect of non-magnetic aluminum Al doping in Mn-site on the critical behavior in La0.57Nd0.1Sr0.33MnO3 compounds using magnetization methods near the Curie temperature TC through various techniques such as modified Arrott plot, Kouvel–Fisher method, and critical isotherm analysis. The values of critical exponents, derived from the magnetic data yield 0.326 ≤β≤0.366,1.265≤γ≤1.342 and 4.13 ≤δ≤5.07. The critical exponents found in this study obey the Widom scaling relation δ=1+γ/β, implying that the obtained values of β and γ are reliable. Experimental results have revealed that the samples exhibited the second-order magnetic phase transition with exponents which match well with those predicted for the three-dimensional Heisenberg (3D) around the critical temperature.

Extrinsic behavior in La0.67Ca0.33MnO3–BaTiO3 composites

A manganite matrix based nano-composite series, (1−x)La0.67Ca0.33MnO3(LCMO)–(x)BaTiO3(BTO), has been prepared by the pyrophoric method. Influence of BTO phase on structural and magneto-transport properties of LCP phase has been studied using structural and transport investigations. The series exhibits a conduction threshold at xm∼0.30. Overall pattern of temperature dependence of resistivity for this series has been fitted with a percolation model. Almost 200% improvement has been observed by the formation of composite when compared to the parent sample.

Evidence for low temperature glassy behavior in La0.5Sr0.5CoO3

We report the observed low temperature spin glass like feature in the optimally doped La0.5Sr0.5CoO3 ferromagnetic system. The characteristic of glassy behavior has been identified by noting (i) the frequency-dependent shift of the low temperature hump position in the out of phase ac susceptibility component; (ii) evolution of freezing temperature with dc biasing field that adheres to de Almeida–Thouless relation; (iii) memory effect; and (iv) sluggish magnetic relaxation. The results of magnetic measurements demonstrate that neither the inter-cluster interaction nor the spin disorder at the interface between ferromagnetic clusters is responsible for the manifestation of such collective glassy behavior. Rather, it is believed to arise from a distinct cluster glass like phase that possibly coexists with the dominant ferromagnetic phase.

Influence of Gd Doping on Magnetic Behavior in La0.67Sr0.33CoO3, La0.67Sr0.33MnO3

Abstract M-T curves, and M-H curves of La 0.67 -x Gd x Sr 0.33 CoO 3, La 0.67 -x Gd x Sr 0.33 MnO 3 ( x =0.00, 0.05, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.67) systems were measured. The results show that with increasing of doping Gd, magnetic structure of the La 0.67 -x Gd x Sr 0.33 CoO 3 system exhibits cluster glass state, and the M-T curves of samples with x ≥0.10 exhibit a peculiar phenomenon that M value rises sharply in a low temperature range; magnetic structure of La 0.67 -x Gd x Sr 0.33 MnO 3 system changes from long-rang ferromagnetic order to cluster glass state, anti-ferromagnetic state, and the M-T curves of samples with x ≥0.50 decline sharply in a low temperature range. The different phenomena shown by the two systems come from different coupling function between Gd and Co, Mn and from spin state transition of Co.

Publisher's Note: “Cluster Co-Existence and DC Field Effect on Re-entrant Spin Freezing Behavior in La0.85Ca0.15Mn0.95Fe0.05O Manganates”

Publisher's Note: “Cluster Co-Existence and DC Field Effect on Re-entrant Spin Freezing Behavior in La_0.85Ca_0.15Mn_0.95Fe_0.05O Manganates”

Publisher's Note: “Cluster Co-Existence and DC Field Effect on Re-entrant Spin Freezing Behavior in La0.85Ca0.15Mn0.95Fe0.05O Manganates”

Publisher's Note: “Cluster Co-Existence and DC Field Effect on Re-entrant Spin Freezing Behavior in La0.85Ca0.15Mn0.95Fe0.05O Manganates”

Effect of low Sr-Ba on the transport and magnetic behaviour of La0.67Ca0.33MnO3

Effect of low Sr-Ba on the transport and magnetic behaviour of La_0.67Ca_0.33MnO₃