Perovskite Manganite La0 Research Articles

Critical Behavior of La0.67Ba0.33Mn0.95Fe0.05O3 Manganite

The critical behavior of perovskite manganite La0.67Ba0.33Mn0.95Fe0.05O3 at the ferromagnetic–paramagnetic has been analyzed. The results show that the sample exhibited the second-order magnetic phase transition. The estimated critical exponents derived from the magnetic data using various such as modified d’Arrott plot Kouvel–Fisher method and critical magnetization M(TC, H). The critical exponents values for the La0.67Ba0.33Mn0.95Fe0.05O3 are close to those expected from the mean field model β = 0.504 ± 0.01 with TC = 275661 ± 0.447 (from the temperature dependence of the spontaneous magnetization below TC), γ = 1.013 ± 0.017 with TC = 276132 ± 0.452 (from the temperature dependence of the inverse initial susceptibility above TC), and δ = 3.0403 ± 0.0003. Moreover, the critical exponents also obey the single scaling equation of M(H, e) = |e|βf±(H/|e|β+γ).

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.

Tricritical point in hole-doped manganite La0.5Ca0.4Li0.1MnO3

The critical behavior of hole-doped perovskite manganite La0.5Ca0.4Li0.1MnO3 has been investigated based on the static magnetization measurement around the second-order paramagnetic-ferromagnetic (PM-FM) transition at 250.5 K. The critical exponents and have been obtained based on both the modified Arrott plot and the Kouvel-Fisher method. The critical isotherm analysis gives . The critical exponents fulfill the Widom scaling relation and obey the single scaling equation , implying the reliability of the obtained exponents. Its relative cooling power (RCP) is found to be scaled with the magnetic field by the law of . The critical-exponent values deduced here approach the theoretical prediction of the tricritical mean-field model, which suggests that the present composition should be close to a tricritical point in the phase diagram of hole-doped manganite La0.5Ca0.5−xLixMnO3.

Structural characterization, magnetic properties and magnetocaloric effects of La0.75Sr0.25Mn1–x Cr x O3 (x = 0.15, 0.20, and 0.25)

The effect of Cr doping on the structural, magnetic and magnetocaloric properties of perovskite manganites La0.75Sr0.25Mn1–x Cr x O3 (x = 0.15, 0.20, and 0.25) has been investigated. Crystalline structure and magnetic properties are investigated by using X-ray powder diffraction and magnetization measurements, respectively. All samples show a single phase and are found to crystallize in the distorted rhombohedral system with $$ R\overline{3} \,c $$ space group. A monotonous change of Curie temperature (T C), from 314 to 253 K, is observed when content doping increases. Substantial magnetic entropy change reaching 4.20 J/kg K is revealed. Relative cooling power was estimated as well. It was found to reach 289, 323, and 386 J/kg for x = 0.15, 0.20, and 0.25, respectively. Field dependence of the magnetic entropy change showing the power law dependence $$ \Delta S_{\rm M} \propto \,\,\left( {\mu_{ 0} \rm H} \right)^{n} $$ is also analyzed and discussed.

Growth and characterization of La0.7Na0.3MnO3 thin films prepared by pulsed laser deposition on different substrates

Perovskite manganite La0.7Na0.3MnO3 thin films were directly grown on MgO (100), Si (100) and glass substrates by pulsed laser deposition. From the XRD patterns, the films are found polycrystalline single-phases rhombohedral. The surface appears porous and cauliflower-like morphology for all LNMO films. LNMO films deposited on the glass substrate were presented smooth morphologies of the top surfaces as compared with other films. The highest magnetoresistance value obtained was −18.86% for LNMO/MgO films at 80K in a 1T magnetic field. Phase transition temperature is 221K for LNMO/Cg, 214K for LNMO/Si and 144K for films deposited on MgO substrates. The films exhibit ferromagnetic transition at a temperature around 286K for LNMO/MgO, 304K for LNMO/Si and 292K for LNMO/Cg thin film. The Curie temperature of LNMO films deposited on the glass substrate, 292K is the highest value that is reported in literature for LNMO films deposited on low-cost amorphous substrates.

Magnetic and transport properties of bilayered perovskite manganites (La0.8Eu0.2)4/3Sr5/3Mn2O7

Samples of (La0.8Eu0.2)4/3Sr5/3Mn2O7 were prepared by solid state reaction method. X-ray diffraction patterns indicated that the sample shows no any asymmetry and no any trace of secondary phase. The magnetization curve as a function of temperature (M-T), the magnetization versus magnetic field (M-H) at different temperatures, and the electron spin resonance spectrum have been detected. The magnetization measurement reveals that with lowing temperature, all of the samples undergo a complex magnetic transition. They transform from the two-dimensional short-range ferromagnetic order at TC2D ≈ 282 K, and enter the three-dimensional long-range ferromagnetic state at TC3D ≈ 259 K. Then they step into the antiferromagnetic state at TN ≈ 208 K and enter electric charge temperature order at TCO ≈ 35 K. The antimagnetic phase is found in the sample (La0.8Eu0.2)4/3Sr5/3Mn2O7below TN. When TC3D=370 K, the paramagnetic phase and antimagnetic phase co-exist. When TC3D is above 370 K, only paramagnetic phase exists in the sample. Besides, through electrical resistivity versus temperature curve ρ-T, the sample shows the maximum magnetization electrical resistivity when metal-insulator transition temperature is reached TP ≈ 80 K, TP being far from TC3D. And the transition shows the phenomenon of intrinsic magnetization electrical resistance, MR ≈ 61%. The resistance begins to increase below TCO. Because of the lowing temperature, the itinerant electron eg becomes increasingly spontaneously localized. One can see from the fitted ρ-T curves that (La0.8Eu0.2)4/3Sr5/3Mn2O7 in high temperature range is in accordance with the small polaron mode range hopping conduction.

Oxygen content and magnetic properties of composites La0.75Sr0.25MnO3±δ calcined at different temperatures

The effects of the calcination temperature on the oxygen content and magnetic properties of the nanocrystalline perovskite manganite La0.75Sr0.25MnO3±δ prepared by the sol–gel method were investigated. The highest temperatures at which the samples were calcined were 973, 1073, 1273, and 1473 K. The X-ray diffraction (XRD) analyses indicate that all the samples have only a single phase with the \( R\bar{3}c \) perovskite structure. As the calcination temperature and calcination time increase, the oxygen content in the samples increases from being deficient to being in excess of that in the stoichiometric formula. The crystallite size also increases from 23 to 283 nm. Magnetic measurements indicate that the sample calcined at 1073 K has the highest Curie temperature. This is owing to the fact that the crystallite cores of this sample have stoichiometric oxygen content. The dependence of the Curie temperature and the saturation magnetization on the calcination temperature are successfully explained.

Magnetic entropy change in perovskite manganites La0.7A0.3MnO3 La0.7A0.3Mn0.9Cr0.1O3 (A = Sr, Ba, Pb) and Banerjee criteria on phase transition

The La0.7A0.3MnO3, La0.7A0.3Mn0.9Cr0.1O3 (A = Sr, Ba, Pb) polycrystalline perovskite manganites sample was prepared by the sol–gel technique. The replacement of partial Mn3+/Mn4+ by Cr3+ (Cr3+ with the same electronic configuration as Mn4+) cause the variety of magnetocaloric property and magnetic entropy change. The maximum magnetic entropy change ΔSH = −1.16 J/kg K and the Relative Cooling Power (about 43.3 J/kg) were obtained from La0.7Sr0.3Mn0.9Cr0.1O3 in the Cr3+ doped series under 1 T magnetic field variation. On this paper, Banerjee criteria had been remarked to distinguish the first-order or second-order phase transition on phase transition of the doped perovskite manganites.

Effect of hydrostatic pressure on magnetic entropy change and critical behavior of the perovskite manganite La0.4Bi0.3Sr0.3MnO3

We report the effect of magnetic field (H) and hydrostatic pressure (P) on the order of magnetic transition of polycrystalline La0.4Bi0.3Sr0.3MnO3 which undergoes a first-order paramagnetic (PM) to ferromagnetic (FM) transition in La0.7−xBixSr0.3MnO3 series. The ferromagnetic Curie temperature (TC) increases with increasing H (12.01 K/T-cooling and 10.28 K/T-warming) and P (8.1 K/kbar-cooling and 6 K/kbar-warming). The first-order FM transition becomes second-order under the applied magnetic field of 9 T and pressure of 9.1 kbar. We have analyzed the critical behavior associated with the second order PM-FM transition at 9.1 kbar. The estimated critical exponents (β = 0.5217, γ = 1.209, and δ = 3.162) are found to be close to the mean-field model. Pressure suppresses metamagnetic transition in magnetization isotherms observed above TC in ambient pressure and enhances the magnetic entropy change (ΔSm). The ΔSm was found to increase by 50% under hydrostatic pressure of 9.1 kbar at TC = 240 K. This study suggested that hydrostatic pressure can be used to enhance magnetocaloric values in phase separated manganites.

Impact of the Oxygen Content on the Electronic Properties in Epitaxial Thin Films of Electron-Doped La&lt;sub&gt;0.9&lt;/sub&gt;Hf&lt;sub&gt;0.1&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt;

Thin films of perovskite manganite La0.9Hf0.1MnO3 (LHMO) have been grown on (100) SrTiO3 single-crystal substrates with different growth pressures by pulsed laser deposition. The different transport behaviors of films have been fitted by various models. The results clearly demonstrate that oxygen pressure is an efficient way to change the transport behaviors of LHMO films. All the transport behaviors observed in LHMO films can be better fitted by Mott’s variable range hopping model than the other two models.

Influence of cobalt on the structural, magnetic and magnetocaloric properties of La0.67Ca0.33MnO3

The critical properties and magnetocaloric effect of perovskite manganite La0.67Ca0.33Mn1−xCoxO3 (x=0.03, 0.1 and 0.15) are investigated. Structural study using Reitveld refinement of X-ray diffraction pattern indicates an orthorhombic structure with Pnma space group for all compositions. The Curie temperature and magnetic moment decrease with increase of cobalt doping concentration and the samples exhibit characteristics of spin/cluster glass state which is evident from magnetization (zero field cooled and field cooled) vs temperature curves. The magnetic data is analyzed in the critical region using the modified Arrott plot method. The obtained values of critical exponents are in agreement with the values predicted by mean field interaction model. LCMCo0.03 compound shows a large magnetic entropy change (ΔSM) of 4J/kgK at a magnetic field of 50kOe. The relative cooling power (RCP) is found to be about ∼184J/kg for LCMCo0.03 and ∼114J/kg in the case of LCMCo0.1 in a magnetic field change of 50kOe. The field dependance of ΔSM and RCP are showing a power dependence at their respective transition temperatures. An increase in resistance and a diminution of magnetic entropy change were observed as a consequence of Co doping. An enhanced magnetoresistance up to 87% and considerable magnetic entropy change were observed for these cobalt doped compounds.

Magnetic and Magnetocaloric Properties of La0.67Pb0.33−x Ag x MnO3 Compounds

In this paper, we have studied the magnetic and magnetocaloric properties of the perovskite manganites La0.67Pb0.33−x Ag x MnO3 (0≤x≤0.15), which show a sharp paramagnetic-ferromagnetic phase transition over a wide temperature range (T=250–401 K). The Curie temperature has been analyzed by two methods: using the numerical derivative dM/dT and the thermodynamic model. The experimental results indicate that T C decreases from 368 to 288 K with increasing Ag substitution independently of the method used to obtain T C. Upon 10 KOe applied magnetic field, the large magnetic-entropy change (|ΔS M|) reaches values of 2.75, 3, 3.25 and 3.5 J/kg K for x=0, 0.05, 0.10 and 0.15 compositions, respectively, which are comparable to that of Gd. The relative cooling power (RCP) increases with increasing Ag content from 68.75 (x=0) to 156.27 J/kg (x=0.15) for ΔH=10 KOe. Through these results, La0.67Pb0.33−x Ag x MnO3 materials are strongly suggested for the use of active refrigerants for magnetic refrigeration technology near room temperature.

Maximum magnetic entropy change modulated toward room temperature in perovskite manganites La0.7−xNdx(Ca,Sr)0.3MnO3

With Nd3+ doping and Ca2+, Sr2+ modulating in the sol–gel technique, a series of polycrystalline perovskite samples La0.7−xNdx(Ca,Sr)0.3MnO3 (x=0, 0.05, 0.1, 0.15, 0.20, 0.25) was prepared, their maximum magnetic entropy changes were tuned to room temperature (ΔSH=−1.47J/kgK at 298k for La0.45Nd0.25(Ca,Sr)0.3MnO3), an enhancement of the maximum magnetic entropy change (ΔSH=−1.89J/kgK at 315k) and its refrigerant capacity (about 45.3J/kg) had also been obtained under 9kOe magnetic field variation for La0.55Nd0.15(Ca,Sr)0.3MnO3 contrast to La0.7(Ca,Sr)0.3MnO3.

Magnetocaloric Effect in Perovskite Manganite La0.65Nd0.05Ba0.3MnO3 with Double Metal–Insulator Peaks

With Nd3+ ionic doping, series of perovskite manganites La0.7−x Nd x Ba0.3MnO3 (x=0, 0.05, 0.1) were prepared by the sol-gel technique. The magnetocaloric correlative measurement of La0.65Nd0.05Ba0.3MnO3 was representatively carried out. Double metal–insulator peaks being found on the resistivity–temperature curves of samples, the maximum of magnetic entropy change was found to be ΔS H=−1.3 J/kg K and its refrigerant capacity 52 J/kg, obtained in the vicinity of room temperature under the variation of 1 T magnetic field. The comparative faint Nd3+ magnetic inhomogeneity submerged in the double-exchange strong magnetic signal along with the differential coefficient of the magnetic moment with temperature, in the physical definition of the magnetic entropy change, resulting in a single peak on the magnetic entropy change curve.

Critical behavior in Co-doped manganites La0.67Pb0.33Mn1−xCoxO3 (0≤x≤0.08)

The critical properties of perovskite manganite La0.67Pb0.33Mn1−xCoxO3 (0≤x≤0.08) around the paramagnetic–ferromagnetic phase transition are investigated through various techniques such as the modified Arrott plot, Kouvel–Fisher method and critical isotherm analysis. Though the nature of this transition was found to be in second order, the estimated critical exponents β (0.233≤β≤0.368), γ (1.03≤γ≤1.40) and δ (4.32≤δ≤5.54) are in between the theoretically predicted values for three-dimensional Heisenberg and tricritical mean-field model. This model suggests the coexistence of the short-range and long-range ferromagnetic orders around the critical temperature. The values of the critical exponents obtained from different methods and the well-obeyed scaling behavior confirm that the calculated exponents are unambiguous and purely intrinsic to the system.

Magnetic entropy change in perovskite manganites La0.6Pr0.1Pb0.3MnO3 with double metal–insulator peaks

Following the double metal–insulator peaks found in series of perovskite manganites La0.7−xPrxPb0.3MnO3 (x=0, 0.05, 0.1), the magnetic entropy change of La0.6Pr0.1Pb0.3MnO3 was carefully investigated as a representative. The maximum magnetic entropy change (ΔSH=−1.7J/kgK at 300K) and the expanded refrigerant capacity (about 123.8J/kg) had been obtained under 10kOe magnetic field variation, though the double peak of maximum magnetic entropy change had not occurred since the comparative faint magnetic signal from the Pr ions inhomogeneity existed in the octahedral frame submerged in the strong magnetic signal originated from the dominating octahedral frame both in the double exchange mechanism, but the width at half maximum in the magnetic entropy change comparatively broadened.

Effects of hole doping in electronic states of La1−xSrxMnO3 probed by magnetic Compton scattering

We have carried out magnetic Compton scattering measurements on polycrystalline samples of the perovskite manganites La1−xSrxMnO3 covering the hole-doping range from x=0.1 to x=0.5. Charge and magnetic Compton profiles were measured in order to obtain Compton profiles of spin-wise subbands. By considering the doping-dependency of the subband Compton profiles, we show how the electronic states evolve associated with hole doping. The results indicate that doped holes predominantly enter into the O 2p states in the lightly doped region and the charge transfer occurs from the up-spin Mn 3d to the down-spin Mn 3d states in the heavily doped region.

Electrical resistivity behaviour of sodium substituted manganites: electron-phonon, electron-electron and electron-magnon interactions

The present paper focuses on a quantitative analysis of the metallic and semiconducting behaviour of electrical resistivity in perovskite manganites La1- x Na x MnO3 (x = 0.1, 0.17). An effective interionic interaction potential (EIoIP) with the long-range Coulomb, van der Waals (vdW) interaction and short-range repulsive interaction up to second neighbour ions within the Hafemeister and Flygare approach was formulated to estimate the Debye and Einstein temperature and was found to be consistent with the available experimental data. For both doping concentration x = 0.1 and 0.17 the electron-phonon, electron-electron and electron-magnon interactions are effective to describe the resistivity behaviour for temperatures less than the metal-insulator transition (T P ). For temperatures, T > T P , the semiconducting nature is discussed with Mott's variable range hopping (VRH) model and small polaron conduction (SPC) model. The fitted density of states as revealed from VRH differs drastically from the experimental value and therefore means the VRH model is not a viable option for describing the resistivity behaviour in high temperature region, T > T P . The SPC model consistently retraces the higher temperature resistivity behaviour (T > θ D /2). The metallic and semiconducting resistivity behaviour of sodium substituted manganites are analysed, to our knowledge, for the first time highlighting the importance of electron-phonon, electron-electron, electron-magnon interactions and small polaron conduction.

Elastic and thermal properties of La1−xSrxMnO3 manganites

The elastic and thermal properties of perovskite manganites La1−xSrxMnO3 (x = 0.165, 0.185, 0.20, 0.40, 0.70, 0.80, 0.90, 1.0) have been studied as a function of temperature (1K≤T≤300K) by means of Atoms in Molecules (AIM) theory and a Modified Rigid Ion Model (MRIM) respectively. The specific heat values (Cv) and the Debye temperatures obtained by us from the lattice contributions are in reasonably good agreement with the available experimental data for some concentrations (x) of La1−xSrxMnO3. In addition, the results on the Bulk Modulus (BT), cohesive energy (ϕ), molecular force constant (f), Reststrahlen frequency (vo) and Grüneisen parameter (γ) are also analysed.

Positive Giant Magnetoresistance in La0.67Sr0.33MnO3/Alq3/Co Organic Spin-Valves

We report a positive spin valve effect—low resistance for parallel electrodes configuration—in organic spin valves fabricated by vacuum thermal evaporation using half-metal perovskite manganites La0.67Sr0.33MnO3 as the bottom electrode, cobalt as the top electrode, and tris(8-hydroxyquinoline) aluminum (Alq3) as the organic semiconductor spacer. A positive giant magnetoresistance (GMR) of ∼12% has been observed at 100 K. The origination mechanism of negative and positive GMR in organic spin valves has been discussed in detail.