Electrical and magnetic properties of La0.67Ba0.33Mn1−x (Me) x O3 perovskite manganites: case of manganese substituted by trivalent (Me = Cr) and tetravalent (Me = Ti) elements

International audienceThe effects of non-magnetic Ti4+ substitution on the structural, electrical and magnetic properties of La0.67Ba0.33Mn1−x Ti x O3 (0≤x≤0.1) are investigated and compared to those existing in La0.67Ba0.33Mn1−x Cr x O3 (magnetic Cr3+). The structural refinement by the Rietveld method revealed that Ti-doped samples crystallize in the cubic lattice with space group Pm3¯m , while samples with Cr crystallize in the hexagonal setting of the rhombohedral R3¯C space group for identical contents of dopant. The most relevant structural features are an increase of the lattice parameters, of the cell volume and of the inter-ionic distances with increasing Ti doping level. Both series of samples show a decrease of the paramagnetic-ferromagnetic transition temperature when the amount of chromium or titanium increases. Transport measurements show that when increasing the metal doping, the resistivity increases whereas the metallic behavior of the parent compound La0.67Ba0.33MnO3 is destroyed. For a substitution higher than 5 at.% of Ti and 10 at.% of Cr, the samples exhibit a semiconducting behavior in the whole range of temperature, for which the electronic transport can be explained by variable range hopping and/or small polaron hopping models

Crossover of the magnetocaloric effect and its importance on the determination of the critical behaviour in the La0.67Ba0.33Mn0.9Cr0.1O3 perovskite manganite

International audienceThe magnetic phase transition and the magnetic entropy change (−ΔSM) in the La0.67Ba0.33Mn0.9Cr0,1O3 manganite were investigated by measuring the magnetization as a function of temperature. The maximum magnetic entropy change (−ΔSM) and the relative cooling power (RCP) are found to be, respectively, 4.20 J kg−1 K−1 and 238 J kg−1 for a 5-T field change, making of this material a promising candidate for magnetic refrigeration near room temperature. To investigate the nature of the paramagnetic (PM) to ferromagnetic (FM) phase transition, found to be of second-order, we performed a critical exponents study by dc-magnetization M(H,T) measurements around the Curie temperature TC, in a temperature range including the critical region |ɛ| = |T − TC|/TC ⩽ 0.05. From the derived values of the critical exponents (β = 0.380, γ = 1.345), we conclude that La0.67Ba0.33Mn0.9Cr0.1O3 belongs to the three-dimensional Heisenberg class with short-range interaction. Scaling relations are obeyed, indicating renormalized interactions around TC. By investigating the field dependence of RCP and ΔSM, it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott method

Impact of the sintering temperature on the structural, magnetic and electrical transport properties of doped La0,67Ba0,33Mn0,9Cr0,1O3 manganite

International audienceA systematic investigation of the La0,67Ba0,33Mn0,9Cr0,1O3 perovskite has been undertaken, mainly to understand the impact of the sintering temperature on the structural, microstructural, magnetic and electrical transport properties in these materials. The La0,67Ba0,33Mn0,9Cr0,1O3 manganite was sintered by a solid-state route at 1000 °C, 1200 °C and 1400 °C. The X-ray diffraction studies show that all samples crystallize with the rombohedral symmetry within the space group R 3 ¯ C, regardless of the sintering temperatures employed in this work. The MnOMn bond angle decreases and the MnO bond length increases with the increase of the grain size. All samples undergo a paramagnetic (PM)-ferromagnetic (FM) phase transition at T=TC. Both the magnetization and the Curie temperature TC decrease with increasing grain size mainly due to the increase of the MnO bond length dMnO. The electrical resistivity (ρ) increases with decreasing grain size because of the enhancement of the grain boundary effect. Low temperature resistivity data below TC was fitted by the relation ρ=ρ0+ρ2T2+ρ4.5T4.5, indicating the importance of the grain/domain boundary, the electron-electron scattering effects and, to a lesser extent, the electron-(magnon,phonon) scattering effects in the mechanism of conduction. On the other hand, the high temperature resistivity above the metal-insulator (M-I) transition Tp for the sample sintered at 1000 °C was explained using variable range hopping (VRH) and small polaron hopping (SPH) models. IR studies revealed that the vibration mode at 411 cm−1, associated with the internal bending of MnO6 octahedra, becomes softer, indicating an increase of the distortion

Structural studies and magnetic and transport properties of Cr-substituted La0.67Ba0.33Mn1−xCrxO3 (0 ≤ x ≤ 0.15) perovskites

International audienceWe have investigated the structural, magnetic and electrical transport properties of a series of ABO3-type perovskite compounds, La0.67Ba0.33Mn1−xCrxO3 (0 ≤ x ≤ 0.15), which strongly depend on the doping level x. The slight difference between the ionic radii of Cr3+ and Mn3+ causes no change in the structure when x ≤ 0.1, remaining rhombohedral (space group R-3C), while for x = 0.15 the structure becomes cubic (space group Pm-3m). Energy dispersive X-ray analysis (EDAX) confirms the expected stoichiometry of all samples. Upon Cr doping on the Mn site, the lattice parameters, the unit cell volume and the BOB bond angle are reduced. All samples present a single magnetic transition from ferromagnetic to paramagnetic phase, showing a decrease of the Curie temperature Tc and the magnetization M when x increases (x ≤ 0.15). However, Cr doping makes the saturation magnetization at 5 K to decrease, which indicates that the Cr3+ moments tend to be antiparallel to the Mn3+ moments at low temperature. The Cr-doped manganites exhibit a large variation in resistivity values. The increase of Cr doping (x ≤ 0.15) leads to an increase of the electrical resistivity. Below 10 at.% of Cr3+, the electrical resistivity shows a metallic behavior, which is well fitted by the relation ρ = ρ0 + ρ2T2 + ρ4.5T4.5, indicating the importance of the grain/domain boundary, the electron-electron scattering effects and, to a lesser extent, the electron-(magnon, phonon) scattering effects in the mechanism of conduction. On the other hand, the 15 at.% of Cr3+ doping makes the material to exhibit a semiconductor behavior, for which the electronic transport can be explained by a variable range hopping (VRH) and small polaron hopping (SPH) models. Results are consistent with a reduction of the number of available hopping sites for the Mn eg (↑) electron due to the substitution of Mn3+ by Cr3+, which suppresses the double exchange (DE) interactions

Room temperature magnetic and magnetocaloric properties of La0.67Ba0.33Mn0.98Ti0.02O3 perovskite

International audienceThe influence of Ti-doping on the magnetic and magnetocaloric properties of La0.67Ba0.33Mn0.98Ti0.02O3 perovskite is investigated. La0.67Ba0.33Mn0.98Ti0.02O3 sample was prepared by ceramic route at 1400 °C. It is a cubic Pm-3m single phase and exhibits a sharp ferromagnetic-paramagnetic (FM-PM) transition at a Curie temperature TC (314 K) which is very close to room temperature. Above TC the data follow a Curie-Weiss law with a shift between experimental and calculated effective paramagnetic moment. The associated experimental magnetic entropy change (ΔSM) and the relative cooling power (RCP) have been determined. The observed field dependence of ΔSM is explained reasonably well by the Landau theory of second order phase transition. The maximum entropy change View the MathML source|ΔSMmax| exhibits a linear dependence with the applied magnetic field. View the MathML source|ΔSMmax| and RCP are respectively 3.21 J kg−1 K−1 (21.48 mJ cm−3 K−1) and 307 J kg−1 (2054 mJ cm−3) at 5 T, which are about 30% of pure Gd. Our results on the magnetocaloric effect (MCE) are compared favourably with reported values for other doped manganites, thus concluding that our sample can be used as a magnetic refrigerant around room temperature

Sol-gel synthesis of ferrites nanoparticles and investigation of their magnetic and photocatalytic activity for degradation of reactive blue 21 dye

International audienc

Critical phenomena and estimation of the spontaneous magnetization through magnetic entropy change in La0.67Ba0.33Mn0.98Ti0.02O3

International audienceThe critical properties of the manganese perovskite La0.67Ba0.33Mn0.98Ti0.02O3 around the paramagnetic-ferromagnetic phase transition were investigated through various techniques such as modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis based on the data of static magnetic measurements recorded around the Curie temperature Tc. The magnetic data analyzed in the critical region using the above methods yield the critical exponents β = 0.551 ± 0.008 with Tc = 310.47 K ± 0.10 (from the temperature dependence of the spontaneous magnetization below TC) and γ = 1.020 ± 0.024 with TC = 310.11 K ± 0.14 (from the temperature dependence of the inverse initial susceptibility above TC) and δ = 2.826, determined separately from the isothermal magnetization at TC. These critical exponents fulfill the Widom scaling relation δ = 1 + γ/β, implying that the obtained values of β and γ are reliable. Based on these critical exponents, the magnetization-field-temperature (M-H-T) data around Tc collapse into two curves obeying the single scaling equation M ( H , ɛ ) = ɛ β f ± ( H / ɛ β + γ ) . The values deduced for the critical exponents in La0.67Ba0.33Mn0.98Ti0.02O3 are close to the theoretical prediction of the mean-field model rather than the universal theory of 3D-Heisenberg, 3D-Ising and tricritical mean-field models. Moreover we have investigated the validity and usefulness of the theoretical modeling in our compound La0.67Ba0.33Mn0.98Ti0.02O3 based on the mean-field analysis of the magnetic entropy change (‑∆SM) versus the magnetization data. Results obtained through this approach are compared to those obtained from extrapolation of the Arrott curves. An excellent agreement was obtained between this approach with the one obtained from the extrapolation of the Arrott curves

Effect of strontium deficiency on the structural, magnetic and magnetocaloric properties of La 0.65 Eu 0.05 Sr 0.3−x MnO 3 (0 ≤ x ≤ 0.15) perovskites

International audienc

On the role of disorder produced by manganese vacancy at the B site on the structural and magnetic properties of L a 0 .67 B a 0 .33 M n 1-x O 3 nanocrystalline

International audienc

Magnetocaloric and Giant Magnetoresistance Effects in La-Ba-Mn-Ti-O Epitaxial Thin Films: Influence of Phase Transition and Magnetic Anisotropy

Magnetic perovskite films have promising properties for use in energy-efficient spintronic devices and magnetic refrigeration. Here, an epitaxial ferromagnetic La0.67Ba0.33Mn0.95Ti0.05O3 (LBMTO-5) thin film was grown on SrTiO3(001) single crystal substrate by pulsed laser deposition. High-resolution X-ray diffraction proved the high crystallinity of the film with tetragonal symmetry. The magnetic, magnetocaloric and magnetoresistance properties at different directions of the applied magnetic field with respect to the ab plane of the film were investigated. An in-plane uni-axial magnetic anisotropy was evidenced. The LBMTO-5 epilayer exhibits a second-order ferromagnetic-paramagnetic phase transition around 234 K together with a metal–semiconductor transition close to this Curie temperature (TC). The magnetic entropy variation under 5 T induction of a magnetic field applied parallel to the film surface reaches a maximum of 17.27 mJ/cm3 K. The relative cooling power is 1400 mJ/cm3 K (53% of the reference value reported for bulk Gd) for the same applied magnetic field. Giant magnetoresistance of about 82% under 5 T is obtained at a temperature close to TC. Defined as the difference between specific resistivity obtained under 5 T with the current flowing along the magnetic easy axis and the magnetic field oriented transversally to the current, parallel and perpendicular to the sample plane, respectively, the in-plane magneto-resistance anisotropy in 5 T is about 9% near the TC