MnO3 Perovskite Manganite Research Articles

Structural, magnetic and magnetocaloric investigations in Pr0.6−xErxCa0.1Sr0.3MnO3 (0 ≤ x ≤ 0.06) manganites

We studied the structural, magnetic and magnetocaloric properties of Pr0.6−xErxCa0.1Sr0.3MnO3 (0 ≤ x ≤ 0.06) perovskite manganites. The samples were synthesized using the solid-state reaction at high temperature and were analyzed by X-ray diffraction and magnetic measurements. X-ray diffraction analysis shows that all compounds were found to be single phase and crystallize in the orthorhombic structure with Pnma space group. Magnetization measurements show that all compounds exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature TC decreases with increasing erbium content from 275 K for x = 0–220 K for x = 0.06. From the M (H) curves, the maximum of the magnetic entropy change |ΔSMmax| under a magnetic field change of 5T was found to be 4.35 J kg−1 K−1 for x = 0.04 which corresponds to a relative cooling power (RCP) about 321 J/kg under the same applied magnetic field. The sensitivity of magnetic entropy change to magnetic field is estimated by the local exponent n (T, μ0H) which determines the field dependence of the experimental |ΔSM|. Moreover, rescaled entropy data for all samples collapses into the same universal curve, revealing universal behavior for the magnetocaloric effect in these compounds.

Chemical and Structural Effects of Lanthanide Trivalent Cation in Ln0.7Sr0.3MnO3(Ln=Pr and Sm) Perovskite Manganite on the Resistive Switching Characteristic

Chemical and Structural Effects of Lanthanide Trivalent Cation in Ln_0.7Sr_0.3MnO₃(Ln=Pr and Sm) Perovskite Manganite on the Resistive Switching Characteristic

Critical behavior near the paramagnetic to ferromagnetic phase transition temperature in La0.67Sr0.1Ca0.23MnO3 compound

The critical behavior of La0.67Sr0.1Ca0.23MnO3 perovskite-manganite was studied around its Curie temperature (TC). Experimental results revealed that this sample underwent a second-order phase transition. Using modified Arrott plot, Kouvel–Fisher method and critical isotherm analysis, the critical parameters (TC, β, γ, and δ) were determined in the two characteristic regions of low- and high-magnetic fields. The estimated critical exponents were close to those expected for three-dimensional Heisenberg class for LSCMO (β = 0.345 ± 0.001, γ = 1.31 ± 0.02 and TC = 294.74 K for μ0H = 0–2 T. However, β = 0.354 ± 0.004, γ = 1.28 ± 0.03 and TC = 294.75 K for μ0H = 3–5 T). These critical exponents fulfill the Widom scaling relation δ = 1 + γ/β, implying the reliability of our values. Based on the critical exponents, the magnetization–field–temperature (M–μ0H–T) data around TC collapses into two curves obeying the single scaling equation M(μ0H, ε) = |ε|β f±(μ0H/|ε|β+γ) where ε = (T − TC)/TC, f+ for T ≻ TC and f− for T ≺ TC. A linear relationship |ΔSMmax(H)|∝Hn was achieved with a local exponent n = 0.58 determined from n = 1+(β − 1)/(β + γ), indicating a short-range FM system.

Investigation of magnetic interactions, electrical and magneto-transport properties in Ga-substituted La0.4Bi0.6MnO3 perovskite manganites

We report on magnetic, electrical and magneto-transport properties in La0.4Bi0.6Mn1−xGaxO3 (with x=0.05 and x=0.1) samples. The phase purity and microstructural analysis of the samples have been carried out using X-ray diffraction and scanning electron microscopy technique. From the magnetization data, the studied samples show paramagnetic to ferromagnetic transition followed with glassy behavior at low temperatures. Frequency dependent ac susceptibility measurements reveal dynamic fluctuations due to cooperative interactions between antiferromagnetic domain pinning effects giving rise to glassy behavior in the studied samples. Electrical resistivity measurements suggest semiconducting behavior for the studied samples in the measured temperature range (100–300K). Our study reveals that resistivity data for T≤ (θD/2, the Debye temperature) follow power law and for T>θD/2 Shklovskii-Efros variable range hopping transport mechanism. The MR% vs. magnetic field has been studied to understand the simultaneous behavior of FM and insulating nature around T=100K existing in the samples.

Room-temperature large magnetocaloric effect and critical behavior in La0.6Dy0.1Sr0.3MnO3

The effect of dysprosium incorporation in La0.7Sr0.3MnO3 perovskite manganite on its magnetic properties, magnetocaloric effect and critical behavior was investigated. The temperature dependent magnetization data exhibit a sharp paramagnetic–ferromagnetic transition at TC=307K, which nature has been identified to be a second-order transition by the scaling laws for magnetocaloric effect. The maximum magnetic entropy change and the relative cooling power are found to be, respectively, 8.314J/kgK and 187J/kg for a 5T magnetic field change without a hysteresis loss, making this material a promising candidate for magnetic refrigeration at room temperature. To study the critical behavior of the paramagnetic–ferromagnetic transition, some related critical exponents (β, γ, and δ) have been also calculated. The values of critical exponents indicate that the present phase transition does not belong to the common transition classes but shows some abnormal variation. We suggest that the induced lattice disordering and magnetic disordering due to Dysprosium incorporation are essential reasons for the presence of a large magnetocaloric effect and of an anomalous ferromagnetic phase transition in the present material

Magnetocaloric Properties in La0.5Ca0.45K0.05MnO3, Pr0.5Sr0.45K0.05MnO3, and Nd0.5Sr0.45K0.05MnO3 Manganites

In this paper, we report the result of the influence of 5 % K doping upon the magnetic and magnetocaloric properties of La0.5Ca0.45K0.05MnO3, Pr0.5Sr0.45 K0.05MnO3, and Nd0.5Sr0.45K0.05MnO3 perovskite manganites. Our samples have been synthesized by the conventional solid-state reaction at high temperature. X-ray diffraction analysis using the Rietveld refinement show that all our synthesized samples are single phase and crystallize in the orthorhombic structure with Pbnm space group for all the compounds. Magnetization measurements versus temperature in a magnetic applied field of 50 mT indicate that all our investigated samples display a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperatures are found to be 295.2, 296.4, and 314 K for La0.5Ca0.45K0.05MnO3 (LCKM), Nd0.5Sr0.45K0.05MnO3 (NSKM), and Pr0.5Sr0.45K0.05MnO3 (PSKM), respectively. From the measured magnetization data as a function of magnetic applied field, we have deduced the associated magnetic entropy change, which reaches a maximum \(\left | {\Delta S}_{\mathrm {M}}^{\text {Max}} \right |\) value of 1.5 1.57 and 1.6 J/kg K for LCKM, PSKM and NSKM respectively under a magnetic applied field of 4 T.

Critical magnetic behavior and large magnetocaloric effect in Pr0.67Ba0.33MnO3 perovskite manganite

We report results of critical magnetic behavior and magnetocaloric investigations of the perovskite manganite Pr0.67Ba0.33MnO3. The compound exhibits a paramagnetic (PM) to ferromagnetic (FM) transition at the Curie temperature TC, and significant negative magnetoresistance in a wide temperature range. To probe the magnetic interactions responsible for the magnetic transitions, we performed a critical exponent analysis in the vicinity of the FM–PM transition region. Magnetic entropy change ΔSM was estimated from isothermal magnetization data. We have found a remarkable large value of |ΔSM| around TC’s, of about 5.50J/kgK for μ0ΔH=4T and a large relative cooling power (~225J/kg). The analysis was done by using the modified Arrot plot (MAP) method. The values of the obtained critical exponents associated with this transition, β=0.366, γ=1.375 and δ=4.743 are close to those expected for the short range 3D Heisenberg model. The model was also confirmed by using |ΔSM|∝(μ0H)n, the field dependence of magnetic entropy change method. The large measured magnetocaloric effect is presumed to arise as a consequence of the sample preparation route.

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.

Deficiency Effect on Magnetic and Magnetocaloric Properties of La0.65−x □ x Ca0.35MnO3 Manganites Synthesized Using Sol–Gel Technique

Magnetic and magnetocaloric properties of La0.65−x □ x Ca0.35MnO3 (≤ x ≤ 0.15) perovskite manganites were investigated. Our polycrystalline samples were elaborated using sol–gel method. The Rietveld refinement shows that all our samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. Lanthanum deficiency leads to a decrease of the unit cell volume. The surface morphology was carried out using scanning electron microscopy (SEM). Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our deficient samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. With increasing lanthanum deficiency, the Curie temperature T c decreases from 275 K for x = 0 to 257 K and for x = 0.15. A large magnetic entropy change |ΔS M |, deduced from isothermal magnetization curves, has been observed in our samples with a peak centred around their respective transition temperature. The maximum of the magnetic entropy change \( \vert {\Delta } S_{M}^{\text {Max}}\vert \) under a magnetic field change of 5 T is found to decrease from 5.11 J/kg/ K for x = 0 to 3.98 J/kg K and for x = 0.15. The relative cooling power decreases from 237.5J/kg for x = 0 to 217.4 J/kg −1 and for x = 0.15.

A-site-deficiency-dependent structural, magnetic and magnetoresistance properties in the Pr0.6Sr0.4MnO3 manganites

Structural, magnetic and magneto-transport properties of Pr0.6Sr0.4MnO3, Pr0.6Sr0.3□0.1MnO3 and Pr0.5□0.1Sr0.4MnO3 perovskite manganite oxides have been investigated. X-ray diffraction (XRD) analysis using Rietveld refinement has shown that all the samples under investigation crystallize in the orthorhombic structure with Pbnm space group. Strontium vacancy leads to an increase in the unit cell volume. Paramagnetic (PM) to ferromagnetic (FM) transitions have been observed in all the synthesized samples. The Curie temperature was found to be 251K for the strontium-deficient sample, 273K for the stoichiometric sample and 275K for the praseodymium-deficient one. With the decrease in temperature, the two deficient samples exhibit semiconducting–metallic transitions. The resistivity decreases while Tρ increases with the change in the magnetic applied field from 0T to 5T. The strontium-vacancy sample has been proven to exhibit a magnetoresistance value of about 50% at 266K at a magnetic applied field of 5T and seems to be constant below 236K. The praseodymium-deficient one is manifested in another form of MR which increases with the decrease in temperature. This is a clear indication of the low field magnétoresistance (LFMR) behavior.

Nanosize effects on the magnetic field induced transitions in La0.67−xEuxCa0.33MnO3 perovskite manganite

The nanosize effects on magnetic field induced transitions in La0.67−xEuxCa0.33MnO3 (x=0.25 and 0.27) system are presented in this paper. The reduction in the particle size of the system shows drastic effects on the electrical transport properties leading to robustness of the charge ordering phenomenon. The metal–insulator transition found in bulk materials at low magnetic fields disappeared in nanoparticles of the same material and a high field induced metal–insulator transition emerged at lower temperatures. These results manifest a strong correlation between the chemical pressures induced by doping of various ions at A-site and nanosize related phenomenon.

Effect of La3+ substitution with Gd3+ on the resistive switching properties of La0.7Sr0.3MnO3 thin films

This study demonstrated that the resistive switching voltage of perovskite manganite material could be controlled by A-site cation substitution in “A” MnO3 perovskite manganite structure. A partial substitution of La3+ in La0.7Sr0.3MnO3 with smaller cation Gd3+ induced A-site vacancy of the largest Sr2+ cation with surface segregation of SrOy due to ionic size mismatch, and the induced vacancies reduced migration energy barrier. The operating voltage decreased from 3.5 V to 2.5 V due to a favorable condition for electrochemical migration and redox of oxygen ions. Moreover, surface-segregated SrOy was enhanced with Gd-substitution and the SrOy reduced Schottky-like barrier height and resistive switching ratio from the potential drop and screening effect. The relationship between A-site vacancy generation resulting in surface segregation of SrOy and resistive switching behavior was also investigated by energy resolved x-ray photoelectron spectroscopy, O 1s near edge x-ray absorption spectroscopy, and current voltage measurement.

Synthesis and Characterization of Thermochromic La0.75Ca0.25MnO3 Perovskite Manganites Nano-powders by Microwave-assisted Solution Combustion Synthesis

The microwave-assisted solution combustion synthesis was developed for application with initially synthesized thermochromic perovskite manganese oxide La0.75Ca0.25MnO3 nano-powders. Dry and very fine powders were obtained after one-step combustion reaction for less than 10 min in a modified domestic microwave oven. The thermal behavior, phase formation and purity of the precursor, and as-synthesized and calcined powders, were investigated by TGA/DTA, X-ray diffraction (XRD) and FT-IR techniques. The morphology of the powder obtained was characterized using a scanning electron microscope (SEM). The XRD pattern and FT-IR results showed that as-synthesized La0.75Ca0.25MnO3 powders were crystalline, and the monophasic perovskite phase occurred with an average crystallite size of 30.46 ± 5.54 nm for 6 h at a relatively low calcination temperature of 900°C. The small particle size obtained by SEM suggested a high specific surface area and high sinterability. This method was found to be simple, rapid and cheap, and an effective way to prepare nano-size perovskite powders.

Magnetocaloric properties in La0.5Ca0.3Na0.2MnO3, Pr0.5Sr0.3Na0.2MnO3 and Nd0.5Sr0.3Na0.2MnO3 manganites

The influence of 20% of Na doping upon the magnetic and magnetocaloric properties of La0.5Ca0.5MnO3, Pr0.5Sr0.5MnO3, and Nd0.5Sr0.5MnO3 perovskite manganites has been investigated. Our samples have been elaborated using the conventional solid state reaction method at high temperature. X-Ray diffraction analysis showed that our synthesized samples are single phase and crystallize in the orthorhombic system with Pbnm space group. Magnetic measurements versus magnetic applied field indicated that the substituted compounds are ferromagnetic at low temperatures. The Curie temperatures are found to be 279, 299 and 292 K for La0.5Ca0.3Na0.2MnO3 (LCNM), Pr0.5Sr0.3Na0.2MnO3 (PSNM), and Nd0.5Sr0.3Na0.2MnO3 (NSNM) respectively. Our samples exhibit an important magnetic entropy change with a maximum |ΔMMax| found to be 1.83, 6.6 and 3.1 J/kgK for LCNM, PSNM and NSNM respectively under a magnetic applied field of 4T.

Investigation of the Properties of Ba-Substituted La0.7Sr0.3−x Ba x MnO3 Perovskite Manganite Films for Resistive Switching Applications

La0.7Sr0.3−xBaxMnO3 (LSBMO: x = 0.09, 0.18, and 0.27) thin films were prepared on Pt-coated Si substrates using a radiofrequency magnetron sputtering technique at a substrate heating temperature of 450°C. The effects of varying the amount of substituted Ba2+ on the physical, chemical, and electrical properties of the perovskite manganite films were systematically investigated. X-Ray diffraction showed that the growth orientation and crystallinity of films were not affected by the amount of substituted Ba cations. Raman spectroscopy was used to determine the tilt of MnO6 octahedra and the Jahn–Teller-type distortion variation of the manganite films. The change in covalent characteristics of Mn–O bonds with increasing amounts of Ba2+ substituent was analyzed by x-ray photoelectron spectroscopy, specifically to examine the effects of bond characteristics on the resistive switching properties of LSBMO. The resistance of the LSBMO films increased with increasing Ba2+ content due to an increase in the covalent nature of Mn–O bonds. The resistive switching ratio increased with increasing Ba2+ amount, and relationships among resistive switching, Jahn–Teller distortion, and Mn–O bond character of LSBMO films were interpreted.

Structural, Magnetic, and Magnetocaloric Properties of La0.5M0.1Sr0.4MnO3 (M=Bi, Eu, Gd, and Dy) Perovskite Manganites

Structural, magnetic, and magnetocaloric properties of La0.5M0.1Sr0.4MnO3 (M=Bi, Eu, Gd, and Dy) powder samples, synthesized using the solid-state reaction at high temperature, have been experimentally investigated. X-ray diffraction analysis using the Rietveld refinement show that La0.5Bi0.1Sr0.4MnO3 sample is single phase and crystallizes in the rhombohedral system with \(R\overline{3}c\) space group whereas a mixture of orthorhombic (Pbnm) and rhombohedral (\(R\overline{3}c\)) phases is observed for M=Eu, Gd, and Dy compounds. The Curie temperature, TC, shifts to lower temperature with decreasing the average A-site ionic radius 〈rA〉, which is consistent with large cationic disorder. Arrott plots show that all our samples exhibit a second order magnetic phase transition. From the measured magnetization data of La0.5M0.1Sr0.4MnO3 (M=Bi, Eu, Gd, and Dy) samples as a function of magnetic applied field, the associated magnetic entropy change |ΔSM| has been determined. In the vicinity of TC, |ΔSM| reached, in a magnetic applied field of 1 T, maximum values of 0.98 J/kg K, 1.01 J/kg K, 0.81 J/kg K, and 0.77 J/kg K for M=Bi, Eu, Gd, and Dy, respectively.

Mechanical properties of bulk and nanostructured La0.61Sr0.39MnO3 perovskite manganite materials

Ultrasonic non-destructive measurement is a versatile and sensitive tool for evaluating the mechanical properties of solids. La0.61Sr0.39MnO3 perovskite magnetic material in bulk and at nanoscale was prepared by solid-state reaction and sonochemical reactor methods, respectively. Evaluation of the mechanical properties of the prepared bulk and nano samples was made through on-line ultrasonic velocity measurements over a wide range of temperature from 300 to 400K. The observed anomalous behaviour in elastic moduli was used to explore the phase transition temperature (Curie temperature TC), that is, from paramagnetic (PM) to ferromagnetic (FM) phase, both in bulk and nanostructured perovskite samples. Further, the behaviour of phase transition both in bulk and nano perovskites was explored through the observed anomalous behaviour.

Magnetic and charge ordering properties of Bi0.6−xEuxCa0.4MnO3 (0.0≤x≤0.6)

We have studied structure, magnetic and transport properties of polycrystalline Bi0.6−xEuxCa0.4MnO3 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) perovskite manganites. Magnetic measurements show that the charge-ordering temperature (TCO) decreases with increasing x up to x=0.4 and then slightly increases with further increasing x up to x=0.6. Further, the antiferromagnetic (AFM) ordering temperature (TN) decreases with increasing x. At T<TN a transition to metamagnetic glass like state is also seen. Eu doping also leads to enhancement in the magnetic moment and a concomitant decrease in resistivity up to x=0.2 and then an increase in resistivity up to x=0.5. We propose that the local lattice distortion induced by the size mismatch between the A-site cations and 6s2 character of Bi3+ lone pair electron are responsible for the observed variation in physical properties.

Temperature-dependent sound velocities, attenuation and elastic moduli anomalies in Pr1− x Sr x MnO3 perovskite manganite materials at 0.28 ≤ X ≤ 0.41

Pr1− x Sr x MnO3 perovskite manganite materials with different compositions of x (x = 0.28, 0.33, 0.35, 0.38 and 0.41) have been prepared using solid-state reaction technique. The ultrasonic longitudinal and shear velocities and longitudinal attenuation have been measured employing through transmission method operated at a fundamental frequency of 5 MHz over a wide range of temperatures. In all the compositions, the temperature-dependent sound velocities, attenuation and elastic constants show interesting anomalies at Curie temperature (T C) and Neel temperature (T N). The observed anomalies at T C and T N have been discussed in terms of phase transition, strength of linear magnetostriction effect and competition between paramagnetism and ferromagnetism.

Magnetic and charge ordering properties of Bi0.6-x(RE)xCa0.4MnO3 (0.0 ≤ x ≤ 0.6) perovskite manganites

In this work, we studied structural, magnetic, and charge ordering properties of polycrystalline Bi0.6−x (RE)x Ca0.4MnO3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) samples, synthesized via solid state reaction route and by taking RE = La, Pr, and Nd, separately. The temperature dependence magnetization measurement reveals that the x = 0.0 compound (BCMO) exhibits a charge ordered (CO) and antiferromagnetic (AFM) phase with the charge ordering temperature (TCO) ∼289 K and the antiferromagnetic ordering temperature (TN) ∼136 K. Only a small fraction of La-dopant in BCMO is sufficient to destroy the CO completely, whereas a large concentration of La (viz., x = 0.2 to x = 0.6) promotes ultimately a paramagnetic to ferromagnetic (PM-FM) transition, and the PM-FM transition temperature (TC) decreases progressively from 241 K to 203 K as x increases from 0.2 to 0.5. In contrast, systematic substitution of Pr or Nd at Bi site induces an intriguing interplay between the charge ordering and antiferromagnetism. Our results demonstrate that the value of TCO decreases with increasing value of “x” and the value of TN increases sharply at both the extremes; however, it remains nearly constant from x = 0.2 to 0.4. In our samples, a glassy magnetic states are also observed at far below the TN.