Transition In La0 Research Articles

Photoinduced ultrafast optical anisotropy encountered by spin-flip transition in La0.67Ca0.33MnO3

Understanding and controlling the transient optical anisotropy of strong correlation systems is of great interest in the quest for information processing and storage. Here, we report on ultrafast optical pump-probe measurements with linearly and circularly polarized laser pulses in the manganite La0.67Ca0.33MnO3 thin film. We show both the time-resolved reflectivity and the polarization state (Kerr rotation and ellipticity) of the probe-pulse at different temperatures, which are analyzed by the ultrafast intersite transition between Mn3+ and Mn4+ sites at photon energies around 1.55 eV. During the temperature-induced dynamical spectral weight transfer, a spin-flip photo-transition between spin up eg states of Mn3+ and spin down eg states of Mn4+ ions occurs and is imprinted on the optical anisotropy of the probe beam.

Mixed magnetic exchange interactions and ferromagnetic diffuse phase transition of La1−xMnO3+δ manganites

Effects of vacancy on the microstructural and magnetic properties in self-doped La[Formula: see text]MnO[Formula: see text] [Formula: see text] manganites have been studied. The samples crystallize in a single phase of rhombohedral structure exhibiting R[Formula: see text]C space group until [Formula: see text]-value reaches 0.2. As self-doped concentration increases, structural distortion is confirmed by combining X-ray diffraction. Ferromagnetic (FM) and antiferromagnetic (AFM) coupling is found and exchange bias effect appears at low temperature. Ferromagnetic diffuse phase transition (FDPT) is induced by Griffiths phase for [Formula: see text] at temperature of [Formula: see text]. The FM transition temperature range is increased from 32 K to 150 K. The enhancement of Griffiths phase with [Formula: see text] for [Formula: see text] is explained by the greater [Formula: see text]-site spatial disorder and the structural distortion.

Static critical behavior of the ferromagnetic transition in La0.67Ba0.33–xZnxMnO3 manganites

ABSTRACTThe critical properties of perovskite manganite La0.67Ba0.33−xZnxMnO3 around the paramagnetic–ferromagnetic phase transition are investigated through various techniques such as modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis. Through the nature of this transition was found to be in second order. The value of critical exponent, derived from the magnetic data using the Kouvel-Fisher method, yields , and 4.600.034.66 ± 0.06 with a TC of 259.98 ± 0.32 − 221.73 ± 0.05 K. The exponent values are close to those expected for three-dimensional Heisenberg ferromagnets with short-range magnetic interaction.

Critical behavior near the paramagnetic to ferromagnetic phase transition temperature in La0.6Sr0.4MnO3 ceramic: A comparison between sol-gel and solid state process

Critical behavior near the paramagnetic (PM) to ferromagnetic (FM) phase transition in La0.6Sr0.4MnO3 ceramics prepared by sol-gel and solid state reaction methods has been systematically investigated. The XRD result coupled with the structural Rietveld refinement method exhibited that all samples crystallized in a rhombohedral structure with a space group of R-3C, which indicated the formation of the perovskite structure of La0.6Sr0.4MnO3. The magnetic data obtained from magnetization measurements indicated a second-order phase transition from PM-FM phase around Curie temperature (TC). Critical exponents, β, γ, and δ values are estimated by various theoretical models such as the modified Arrott plot (MAP), the Kouvel-Fisher plot (KF) and the critical isotherm (CI) techniques. Grain size dependence of the critical behavior of La0.6Sr0.4MnO3 samples with different sizes from nano-scale to mic-scale was detected by fitting the experimental data to the theoretical models.

Studies on magnetic field and temperature driven magneto-structural phase transition in La0.5Sr0.5MnO3+δ

Abstract The influence of magnetic field on the crystal structure of colossal magnetoresistance (CMR) material La 0.5 Sr 0.5 MnO 3+δ has been investigated. Low temperature high-magnetic field powder X-ray diffraction (XRD) measurements were carried out on La 0.5 Sr 0.5 MnO 3+δ in temperature range from 4.2 to 300 K and magnetic field range from 0 to 8 T. A first order structural phase transition from tetragonal I 4/ mcm to orthorhombic Fmmm phase, coupled with reported electronic and magnetic phase transition from ferromagnetic metal to antiferromagnetic insulator state has been started at ∼200 K and completed at ∼100 K. On the application of 8 T magnetic field this magneto-structural phase transition shifted to lower temperature (∼162 K) with phase coexistence regime down to 4.2 K. Isothermal X-ray diffraction measurements at 150 K infer the evidence of magnetic field driven first order structural phase transition from Fmmm to I 4/ mcm . These results consistent with the resistivity and magnetoresistance results; present the microscopic evidence of strong spin-lattice coupling and reveal the magnetic field driven structural phase transition as the origin of observed colossal magnetoresistance in this material.

Magnetotransport at the LTO-LTT Structural Transition in La1.48Nd0.4Sr0.12CuO4

Magnetoresistance (MR) was measured in a La1.48Nd0.4Sr0.12CuO4 single crystal in perpendicular magnetic fields H up to 9 T in the region of the structural transition from the low-temperature orthorhombic (LTO) to low-temperature tetragonal (LTT) phase. The hysteretic MR exhibits discrete jumps or avalanches only when the transition is approached from the LTT phase, and only during the first field sweep. The properties of the hysteresis are found to be independent of the field driving rate. The results are consistent with the presence of magnetostructural domains coupled with the charge degrees of freedom.

Spin transitions in La0.7 Ba0.3CoO3 thin films revealed by combining Raman spectroscopy and X-ray diffraction

In cobaltite, the spin states transitions of Co3+/4+ ions govern the magnetic and electronic conduction properties. These transitions are strain-sensitive and can be varied using external parameters, including temperature, hydrostatic pressure, or chemical stresses through ionic substitutions. In this work, using temperature dependent Raman spectroscopy and X-ray diffraction, the epitaxial strain effects on both structural and vibrational properties of La0.7 Ba0.3 CoO3 (LBCO) cobaltite thin films are investigated. All Raman active phonon modes as well as the structure are found to be strongly affected. Both Raman modes and lattice parameter evolutions show temperature changes correlated with magnetic and electronic transitions properties. Combining Raman spectroscopy and X-ray diffraction appears as a powerful approach to probe the spin transition in thin film cobaltite. Our results provide insight into strong spin-charge-phonon coupling in LBCO thin film. This coupling manifests as vibrational transition with temperature in the Raman spectra near the ferromagnetic spin ordered transition at 220 K.

Critical behavior near the paramagnetic-ferromagnetic phase transition in polycrystalline La0.6Ca0.2Ba0.15□0.05MnO3

In this paper, we present a detailed study on the structural and critical behavior around paramagnetic (PM)-ferromagnetic (FM) phase transition in La0.6Ca0.2Ba0.15□0.05MnO3 (LCBMO). Our powder specimen was synthesized using the conventional solid-state reaction method and was analyzed by X-ray diffraction and magnetic measurements. X-ray diffraction analysis, at room temperature, shows that LCBMO adopts an orthorhombic structure with Pbnm space group. Detailed analyses of magnetic-field dependences of magnetization in the vicinity of the paramagnetic-ferromagnetic transition, M(H,T), reveal that LCBMO undergoes a second-order magnetic phase transition. Critical behavior has been studied through various techniques such as modified Arrott plot (MAP), Kouvel-Fisher method (KF) and critical isotherm (CI) analysis. The estimated Critical exponents are close to those expected for the mean-field model (β=0.5, γ=1 and δ=3). The reliability of the critical exponent values was confirmed by the Widom scaling relation, as well as the universal scaling hypothesis.

Effect of annealing on Curie temperature and phase transition in La0.55Sr0.08Mn0.37O3 epitaxial films grown on SrTiO3 (100) substrates by reactive radio frequency magnetron sputtering

Mn-poor LaSrMnO3 (LSMO) epitaxial films were grown on SrTiO3 (100) substrates by radio frequency magnetron sputtering in an argon and oxygen gas mix, and then the samples were annealed in air at various temperatures (Ta). 2 theta-chi X-ray diffraction mapping, nano-beam diffraction analysis through transmission electron microscopy, and electron back scatter diffraction through scanning electron microscopy revealed that the crystal symmetry of the LSMO films changed from monoclinic/orthorhombic to rhombohedral on annealing in air. Curie temperature (TC) of the LSMO films was found to increase with increasing Ta, and become higher than the room temperature at Ta≥861°C, indicating that the cause of these changes was the filling of oxygen and the transition of the crystal symmetry into rhombohedral.

Crystal structure and magnetic behavior of the La0.1Bi0.9FeO3 compound

The nano-crystalline La0.1Bi0.9FeO3 compound was successfully synthesized by starch-based combustion method. The crystal structure and magnetic behavior were studied by temperature-dependent X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and magnetic measurements. The La0.1Bi0.9FeO3 compounds crystallized in a rhombohedrally distorted perovskite structure with space group R3c. The substitution of La for Bi reduced the rhombohedral distortion. The structural phase transitions in La0.1Bi0.9FeO3 driven by temperature showed that the extraordinary two-phase coexistence state of BiFeO3 and LaFeO3 was observed in a narrow temperature range of 630–700 °C. The magnetization of the La0.1Bi0.9FeO3 sample was improved by heat treatment in the temperature range. When the heat treatment temperatures rose from 25 to 600 °C, the remanence (Mr) and coercivity (Hc) of the La0.1Bi0.9FeO3 compound almost remained the same, and increased rapidly to 0.134 emu/g and 7.1 KOe on further increasing the heat treatment temperature to 650 °C.

Magnetic, Magnetocaloric and Master Curve Behaviors for La0.6Sr0.4Mn0.9V0.1O3 Compound

This paper reports the magnetic and magnetocaloric properties of La0.6Sr0.4Mn0.9V0.1O3 polycrystalline manganite elaborated using the solid-state reaction method. The X-ray powder diffraction shows that the prepared compound has a single phase. Magnetocaloric effect is calculated from the measurement of initial isothermal magnetization versus magnetic field at various temperatures. The enhanced relative cooling power (RCP) and \({\Delta } S_{\mathrm {M}}^{\max }\) values show that this sample has potentials for future technological application. Moreover, we have studied the universal behavior used as a further criterion to distinguish the order of the phase transition in La0.6Sr0.4Mn0.9V0.1O3.

Disorder-driven phase transition in La0.37D0.30Ca0.33MnO3 (D = Bi, Sm) manganites

In the present work we report the structural, electron spin resonance (ESR) and magnetic properties of La0.37D0.30Ca0.33MnO3 (D = Bi, Sm) manganites synthesized by sol-gel method. The critical behavior at the critical point, where the system undergoes phase transition from paramagnetic (PM) to ferromagnetic (FM) state, is investigated by using modified-Arrott plots, Kouvel-Fisher method and critical isotherm analysis. Both the samples show second-order phase transition near the critical point. The decrease in magnetization (M), Curie temperature (TC), evolution of spin or cluster glass behavior and the nature of second-order phase transition compared to the first-order transition reported in the literature for La0.67Ca0.33MnO3 are ascribed to disorder caused by the size mismatch of the A-site cations with Bi and Sm doping at La-site.

Second order magnetic phase transition and scaling analysis in iron doped manganite La0.7Ca0.3Mn1−xFexO3 compounds

We investigated magnetic properties of La0.7Ca0.3Mn1−xFexO3 (x=0.09 and 0.11) compounds in terms of isothermal magnetization analysis and scaling behavior with various critical exponents. From the Landau theory of magnetic phase transition, we found that the paramagnetic to ferromagnetic phase transition in La0.7Ca0.3Mn1−xFexO3 (x=0.09 and 0.11) compounds is the type of second order magnetic transition (SOMT), which contrary to the first order magnetic transition (FOMT) for low Fe-doped compounds (x<0.09) in previous reports. When we investigate the critical behavior of the compounds near T=Tc by the modified Arrott plot, Kouvel–Fisher plots, and critical isothermal analysis, the estimated critical exponents β, γ, and δ are in between the theoretically predicted values for three-dimensional Heisenberg and mean-field interaction models. It is noteworthy that the scaling relations are obeyed in terms of renormalization magnetization m=ε−βM(H,ε) and renormalized field h=|ε|β+γH. Temperature-dependent effective exponents βeff and γeff correspond to the ones of disordered ferromagnets. It is shown that the magnetic state of the compounds is not fully described by the conventional localized-spin interaction model because the ferromagnetic interaction has itinerant character by increasing Fe-doping concentration.

Calculation of the H–T phase diagram, magnetization and susceptibility in layered structures

The magnetic field–temperature (H–T) phase diagram is calculated using the mean field theory by expanding the free energy in terms of the uniform and staggered magnetization for the ferromagnetic–antiferromagnetic transitions in the La0.6Nd0.4Mn2Si2 multilayer structures. Using our experimental measurements, analysis of the magnetization as a function of the magnetic field at constant temperatures from 45K to 250K is performed by a power-law formula close to the ferromagnetic–antiferromagnetic transitions. Also, by obtaining the magnetic field dependence of the isothermal susceptibility χT from the M–H curves, χT vs. H−Hc is analyzed (Hc is the critical magnetic field) using a power-law formula for the antiferromagnetic–ferromagnetic (AF–FM) transitions in La0.6Nd0.4Mn2Si2. It is found that a discontinuous (first order) transition which occurs at the lowest (45K) and the highest (250K) temperatures, changes to a continuous one at a constant temperature at around 100K as the magnetic field carries the systems from the antiferromagnetic to the ferromagnetic phase. Values of the critical exponents associated with this transition are deduced and they are compared with the predictions of some theoretical models.

Effect of injected spins with different polarized orientations on the vortex phase transition in La0.7Sr0.3MnO3/La1.85Sr0.15CuO4 heterostructure

The current-voltage (I-V) characteristics with spin injection were investigated for the epitaxial La0.7Sr0.3MnO3/La1.85Sr0.15CuO4 heterostructure rotated from H//c to H//ab in magnetic fields up to 14 T. It is found that all the I-V curves in various magnetic fields can be scaled with a three dimensional (3D) vortex glass model, and the spin injection can induce a better 3D scaling behavior, which is closely related to the decrease of the anisotropy parameter. A vortex phase diagram for the evolution of vortex glass transition field (Hg) and upper critical field (Hc2) indicates that both Hg and Hc2 are suppressed by spin injection, and this effect becomes more obvious in the case of H//ab, which probably originates from the different suppression on the superconducting pairing strength by different injected spins' orientations.

Influence of Ce addition on the structural, magnetic, and magnetocaloric properties in La0.7−xCexSr0.3MnO3 (0≤x≤0.3) ceramic compound

We report improvement in the magnetocaloric properties of Ce-doped lanthanum manganites. Polycrystalline La0.7−xCexSr0.30MnO3 (0≤x≥0.3) samples were prepared using the conventional solid-state reaction method with phase purity and structure confirmed using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order ferromagnetic transition in parent sample and as well as in doped sample with Curie temperature decreasing progressively with increasing Ce-concentration from ~370K for x=0.0 to 310K for x=0.30. Magnetic entropy change (ΔSM) was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field dependent magnetization curves. A large ΔSM associated with the ferromagnetic–paramagnetic transition in La0.7−xCexSr0.30MnO3 samples has been observed. The value of ΔSM was found to increase with Ce-doping up to x=0.15 and the highest value of 2.12Jkg−1K−1 (at ΔH=2T) was observed for La0.55Ce0.15Sr0.30MnO3 sample near the Curie temperature of 356K. Also, improved relative cooling power of ~122Jkg−1 was observed for the same sample. Due to the large magnetic entropy change and high Curie temperature, the La0.55Ce0.15Sr0.30MnO3 sample is suggested to be used as potential magnetic refrigerants for magnetic refrigeration technology above room temperature.

Direct measurement of the low temperature spin state transitions in La1−xSrxCoO3 (0.05 &amp;lt; x &amp;lt; 0.3)

Sr-doped LaCoO3 has a complex magnetic phase diagram, which is believed to be directly correlated to changes in the crystal structure and ordering of the Co3+ spin states. In this work, we study the low temperature Co3+-ion spin state transitions in Sr-doped LaCoO3 around the critical doping concentration where a metal to insulator transition has been observed using electron energy-loss spectroscopy of the O K-edge combined with the Co L-edge fine structure. We measure the local spin state of the Co3+-ions and we demonstrate that the Co3+ spin-state transition only occurs in La0.95Sr0.05CoO3 single-crystal materials in the temperature range accessible by LN2 in-situ cooling, while no structural symmetry change is observed. The presence of this low-temperature spin-state transition in La1−xSrxCoO3 (x &amp;lt; 0.17) has been proposed as the origin of the percolative magnetic ordering in doped LaCoO3.

Grain size modification in the magnetocaloric and non-magnetocaloric transitions in La0.5Ca0.5MnO3 probed by direct and indirect methods

The influence of grain size in the magnetic properties of phase separated manganites is an important issue evidenced more than a decade ago. The formation of long range ordered phases is suppressed as the grain size decreases giving place to a metastable state instead of the ground state. In this work, we present a study of the magnetocaloric effect in the prototypical manganite La0.5Ca0.5MnO3 as a function of the grain size. The differences obtained using direct and indirect methods are discussed in the framework of domain walls in the ferromagnetic phase of the system.

Critical behavior near the ferromagnetic–paramagnetic phase transition in La0.65Eu0.05Sr0.3Mn1−xCrxO3 (x=0.10 and x=0.15)

The critical properties of perovskite manganite La0.65Eu0.05Sr0.3Mn1−xCrxO3 (x=0.10 and x=0.15) around the paramagnetic–ferromagnetic phase transition are investigated through various techniques such as the modified Arrott plot, Kouvel–Fisher method, and critical isotherm analysis. The experimental results have revealed that the samples exhibited the second-order magnetic phase transition and the critical exponents of β and γ for La0.65Eu0.05Sr0.3Mn1−xCrxO3 (x=0.10) are consistent with the prediction of the mean field model. Furthermore, the estimated critical exponents of La0.65Eu0.05Sr0.3Mn1−xCrxO3 (x=0.15) are close to those found out by the 3D-Heisenberg model. The magnetization–field–temperature M–H–T behaviors of all compounds at below and above TC were properly renormalized following the scaling of state equation M(H,ε)=|ε|βf±(H/|ε|β+γ), where ε=(T−TC)/TC, f+ for T>TC and f− for T<TC. This confirms that the obtained values of the critical exponent as well as TC are reasonably accurate and unambiguous.

Electronic transport and conduction mechanism transition in La1∕3Sr2∕3FeO3 thin films

We report on the electronic transport properties of epitaxial La1∕3Sr2∕3FeO3 films using temperature dependent resistivity, Hall effect, and magnetoresistance measurements. We show that the electronic phase transition, which occurs near 190 K, results in a change in conduction mechanism from nonadiabatic polaron transport at high temperatures to resistivity behavior following a power law temperature dependence at low temperatures. The phase transition is also accompanied by an abrupt increase in apparent mobility and Hall coefficient below the critical temperature (T*). We argue that the exotic low temperature transport properties are a consequence of the unusually long-range periodicity of the antiferromagnetic ordering, which also couples to the electronic transport in the form of a negative magnetoresistance below T* and a sign reversal of the Hall coefficient at T*. By comparing films of differing thicknesses, stoichiometry, and strain states, we demonstrate that the observed conduction behavior is a robust feature of La1∕3Sr2∕3FeO3.