MnO3 Compound Research Articles

Modeling and Prediction Investigation of the Resistivity of the Perovskite La0.57Y0.10Ba0.23Ca0.10MnO3 Compound

Modeling and Prediction Investigation of the Resistivity of the Perovskite La0.57Y0.10Ba0.23Ca0.10MnO3 Compound

Impact of Gd ion substitution on the magneto-caloric effect of La0.6-xGdxSr0.4MnO3 (x = 0, 0.0125, 0.05, 0.10) manganites

Abstract The effect of slight changes of the chemical composition on Magneto-caloric properties of manganite was investigated on a series of ceramic nano-particles of La0.6-xGdxSr0.4MnO3 (x = 0, 0.0125, 0.05, 0.10) where they synthesized using the Sol-gel method. The X-ray powder diffraction data and the Rietveld refinement analysis indicated that the gradual replacement of La with Gd reduced the cell volume acting in a comparable manner to applying external pressure. Similarly, the magnetization measurements as a function of temperature on all La0.6-xGdxSr0.4MnO3 samples showed a ferromagnetic transition, in which the transition temperature reduced as x increased. The calculated magnetic entropies of all samples of La0.6-xGdxSr0.4MnO3 as a function of temperature suggest a magneto-caloric effect similar to that of pure Gd. These results provide evidence that La0.6-xGdxSr0.4MnO3 compounds have a potential for magnetic refrigeration application.

Study of complex impedance spectroscopic properties of La0.7-x Dy x Sr0.3MnO3 perovskite oxides.

The dysprosium perovskite La0.7−xDyxSr0.3MnO3 (x = 0.00 [LSMO] and 0.03 [LDSMO]) compounds were prepared by the sol–gel reaction and characterized by the X-ray diffraction technique. The electrical conductivity and modulus characteristics of the system have been investigated in the temperature and the frequency range 311–356 K and 209–5 × 107 Hz, respectively, by means of impedance spectroscopy. The ac and dc conductivities were studied to explore the mechanisms of conduction of LSMO and LDSMO. The insertion of a small amount of Dy3+ in the La-site of LSMO perovskite oxide increases the value of the activation energy from 0.2106 to 0.5357 eV and enhances electrical resistivity values for almost two orders of magnitude.

Effect of NiO impurity on the magneto-transport properties of the La0.7Ba0.3MnO3 granular manganite

Magnetoresistive, magnetic and thermoelectric properties of the La0.7Ba0.3MnO3/xNiO system are studied. The x-ray diffraction shows the coexistence of the NiO and the La0.7Ba0.3MnO3 phases in doped composites, revealing their interaction lack. This suggests the precipitation of the NiO at grain boundaries and on the La0.7Ba0.3MnO3 surface, interrupting the conduction between grains. Hindering the direct contact between the La0.7Ba0.3MnO3 grains increases the resistivity and decreases the metal-semiconductor transition temperature, leading to the spin tunneling effect. This enhances the room temperature magnetoresistance of the La0.7Ba0.3MnO3 compound from −11.25% to −42.7% and −17.24% for 5% and 20% of the NiO additive amount, respectively. The pristine La0.7Ba0.3MnO3 compound shows a Curie temperature value of 348 K that fluctuates negligibly with the NiO addition. However, it decreases to 332 K at the x = 0.05 composite due to a tiny diffusion of NiO in the La0.7Ba0.3MnO3 lattice at this composite. The thermoelectric power properties of the La0.7Ba0.3MnO3 compound are changed with the NiO addition. Where the hole conduction interval increases and the peak of the Seebeck coefficient is shifted towards higher temperatures.

Tuning the magnetic and magnetotransport properties of Pr0.8Sr0.2MnO3 manganites through Bi-doping

Magnetic and magneto-transport properties of Pr0.8−xBixSr0.2MnO3 (x = 0, 0.05 and 0.1) compounds were investigated. All samples exhibited a second-order paramagnetic-ferromagnetic transition with the decrease in temperature. The Curie temperature decreased from 210 to 140 K with the Bi-doping content. The electrical resistivity of the parent sample was described by the phenomenological percolation model, which is based on the phase segregation. The metallic character observed in the pristine sample was reduced, and then entirely suppressed by 10% of Bi. The resistivity data for doped samples were described using Mott’s variable range hopping model at high temperatures and by electron-electron interaction and inelastic scattering mechanisms at low temperatures. A Colossal magnetoresistance (MR) was observed in the studied samples. The parent sample illustrated the predominance of intrinsic MR but in doped compounds, MR curves revealed the coexistence of intrinsic and extrinsic contributions. Bi-doping was found to enhance the extrinsic MR in Pr0.8−xBixSr0.2MnO3 (0 ≤ x ≤ 0.1) samples.

A comparative study of polaronic transport in paramagnetic state of bulk and nanocrystalline La0.46Ca0.54MnO3 compound

In this present study, electronic transport and magneto-transport properties of bulk and nanocrystalline La0.46Ca0.54MnO3 compound are reported. The activation energies required for polaron transport in the paramagnetic state for different average grain size particles were estimated from the resistivity as a function of temperature data. It is found that there is a strong dependency of the activation energy in paramagnetic state with the reduction of the grain sizes and charge ordering. With decreasing particle sizes, activation energy enhances and it modifies with the application of external magnetic field. However, a different nature was found for the 15 and 21 nm particle size samples. The activation energy for the 21 nm particle size sample is smaller compared to 15 nm. Such behavior may be associated with the more disorder and spin-pinning effect in the lowest particle size sample. The variation of activation energy and the crystallographic unit cell volume with the reduction of particle size is addressed.

Instability of insulator state towards nanocrystallinity in [formula omitted] compound: Enhancement of low field magnetoresistance

The present study shows the modification of the insulator state to metallic state with reduction of particle size in (La0.5Y0.5)0.7Ca0.3MnO3 compound by magnetotransport measurements. The decrease in the activation energy as well as increase in the effective density of states near Fermi level is observed with particle size reduction. This modification leads to the decrease in the resistivity in the nanoparticle in the low-temperature regime (T<150K). On the other hand, the temperature dependent dc susceptibility data shows the evolution of the non-Griffiths phase to Griffiths phase with reduction of particle size in the temperature range 100K<T⩽200K. This evolution from non-Griffiths phase to Griffiths phase leads to the formation of large ferromagnetic clusters at the expense of antiferromagnetic interactions which is responsible for the non-Griffiths phase. The presence of the large ferromagnetic clusters helps to create percolation path for electronic transport and is the probable reason for the enhancement of magnetoresistance in this temperature range. On the other hand, enhancement of low field magnetoresistance (LFMR) observed below 100 K has been attributed to the increased spin polarized tunneling (SPT) component due to the increase in the size of the ferromagnetic clusters in the nanoparticle compares with that of bulk.

Evolution from Griffiths like phase to non-Griffiths like phase with Y doping in [formula omitted

Detailed analysis of the temperature dependent dc susceptibility data shows the modification from the Griffiths like phase (GP) to non-Griffiths like phase (non-GP) in (La1-xYx)0.7Ca0.3MnO3(x=0,0.3,0.4,0.5,0.6) compounds with x. The existence of non-Griffiths phase is revealed from the upward deviation of the inverse susceptibility (1/χ) versus temperature plot from the Curie-Weiss behavior for the compounds with x⩾0.5. Whereas Griffiths phase is identified from the downturn of 1/χ versus T plot from the Curie-Weiss line in the compounds with x=0.3,0.4. The increased lattice distortion (with x) decreases the M-O-Mn bond angle and at the same time increase the electron-phonon (e-ph) coupling which in turn decreases the ferromagnetic double exchange (DE) interactions and enhances the effective short-range antiferromagnetic superexchange interactions between Mn3+/Mn3+ and Mn4+/Mn4+ ions above the Curie temperature (TC). The enhancement of this short-range antiferromagnetic (SR-AFM) interactions have been attributed to the conversions from GP to non-GP phase. The increased SR-AFM interactions with Y doping has also been substantiated from the magnetocaloric study.

Spontaneous Magnetization Estimation and Magnetocaloric Effect Study by Means of Theoretical Models in La0.67Pb0.33MnO3

In this work, the dependence of the spontaneous magnetization on temperature of La0.67Pb0.33MnO3 manganite has been experimentally estimated from the Arrot plots and from the magnetic entropy change. The magnetocaloric effect (MCE) in this sample has been simulated by the Landau theory and the phenomenological model. Theoretical simulations correlated well with the experimental results. A secondorder ferromagnetic-paramagnetic (FM-PM) phase transition has been proved for La0.67Pb0.33MnO3 compound.

Magnetic properties and magnetocaloric effect of Sr-doped Pr0.7Ca0.3MnO3 compounds

In this work, we pointed out that Sr substitution for Ca leads to modify the magnetic and magnetocaloric properties of Pr0.7Ca0.3-xSrxMnO3 compounds. Analyzing temperature dependence of magnetization, M(T), proves that the Curie temperature (TC) increased with increasing Sr content (x); TC value is found to be 130–260 K for x = 0.0–0.3, respectively. Using the phenomenological model and M(T,H) data measured at several applied magnetic field, the magnetocaloric effect of Pr0.7Ca0.3-xSrxMnO3 compounds has been investigated through their temperature and magnetic field dependences of magnetic entropy change ΔSm(T,H) and the change of the specific heat change ΔCP(T,H). Under an applied magnetic field change of 10 kOe, the maximum value of -ΔSm is found to be about 3 J/kg·K, and the maximum and minimum values of ΔCP(T) calculated to be about ±60 J/kg·K for x = 0.3 sample. Additionally, the critical behaviors of Pr0.7Ca0.3-xSrxMnO3 compounds around their TC have been also analyzed. Results suggested a coexistence of the ferromagnetic short- and long-range interactions in samples. Moreover, Sr-doping favors establishing the short-range interactions.

Significantly large magnetocaloric effect in polycrystalline La0.83Sr0.17MnO3 near room temperature

We have observed a significantly large magnetocaloric effect near room temperature for polycrystalline ferromagnetic La0.83Sr0.17MnO3 compound. The maximum value of the magnetic entropy change at the vicinity of the paramagnetic to ferromagnetic ordering temperature is about 8.0 J/kg-K in the presence of a 70 kOe external magnetic field. The present study indicates that the magnetic entropy change near room temperature is comparable to (or larger than) that for the suggested refrigerant materials reported earlier.

A theoretical approach to study the magnetic and magnetocaloric properties in lanthanum manganites

We studied the magnetic and magnetocaloric properties of (La, A)MnO3 (A = divalent metal) compounds on basis of the double-exchange Kubo-Ohata model considering magnetoelastic interactions. The adequacy of the calculations is demonstrated by comparison with experimental magnetization curves for the La0.69Pb0.31MnO3 and La0.75Ca0.25MnO3 compounds. For the case of divalent admixture La2/3(Ca1-xSrx)1/3MnO3 we calculated successfully the isothermal magnetocaloric potential for this series of compounds. Additionally, we showed a correlation between the compressibility and the η-parameter which defines the order of the transition.

Self-assembled impurity and its effect on magnetic and magnetocaloric properties of manganites

This work investigates the effect of self-assembled impurities on magnetic and magnetocaloric properties of the La0.3Ba0.7MnO3 and the La0.3Sr0.7MnO3 compounds. The x-ray diffraction patterns show multiple secondary phases in the as prepared conditions due to the incomplete interaction among reactants. However, the homogeneity is enhanced gradually by increasing the sintering temperature until a high purity phase is obtained at the 1200 °C sintering temperature. Results show that the magnetic and the magnetocaloric properties are promoted with the homogeneity and sintering temperature, where there is a monotonic increase in the saturation magnetization and the Curie temperature with the increase of sintering temperature. In addition, the magnetic entropy change of the La0.3Sr0.7MnO3 compound increases from 0.1 J/kgK for the as prepared condition to 0.2 J/kg K and 0.8 J/kg K for the 800 °C and the 1200 °C sintering temperatures, respectively. And for the La0.3Ba0.7MnO3 compound, the magnetic entropy change shows the values of 0.35 J/kg K and 0.78 J/kg K for the 800 °C and 1200 °C sintering temperatures respectively.

Unconventional critical behavior near the phase transition temperature and magnetocaloric effect in La0.5Ca0.4Ag0.1MnO3 compound

The critical behavior associated with the magnetic phase transition has been investigated by magnetization isotherms in La0.5Ca0.4 Ag0.1MnO3 (LCAMO) powder. The X-ray diffraction characterization has revealed that this sample crystallized in the orthorhombic symmetry with Pnma space group. While the experimental results revealed that this sample underwent a paramagnetic-ferromagnetic transition, the magnetic measurements data indicated that the compound exhibited a second-order phase transition. Furthermore, the critical exponents values were found as β = 0.79, γ = 0.71 and δ = 1.828 with TC = 189.87 K. The relative cooling power of the sample was determined as 14.70 J/kg under a magnetic field of 1 T making it a potential working material in magnetic refrigeration.

Importance of the synthesis and sintering methods on the properties of manganite ceramics: The example of La0.7Ca0.3MnO3

The influence of the synthesis and sintering methods on the structural, microstructural, stoichiometry and thus the magnetocaloric properties of the La0.7Ca0.3MnO3 compound has been thoroughly studied. Soft-chemistry (sol-gel and polyol) synthesis and spark plasma sintering (SPS) procedures, used to obtain nanostructured materials, were compared to the traditional ceramic ones. This work evidences that SPS treatment not only reduces the grain size but also leads to oxygen sub-stoichiometry. This entails a lower Mn4+ content in the manganite, and probably heterogeneity in the Mn4+ grain distribution, which have consequences on the magnetic and magnetocaloric properties: a lower maximum entropy variation which is compensated by a larger transition temperature range. The sample prepared by combining polyol soft-chemistry synthesis and SPS sintering displays a higher maximum relative cooling power value, equal to 70% of that of gadolinium, the most effective material for domestic magnetic refrigeration.

Effect of nanostructure on thermoelectric properties of La0.7Sr0.3MnO3 in 300–600 K temperature range

In oxide materials, nanostructuring effect has been found a very promising approach for the enhancement of figure-of-merit, ZT. In the present work, we have synthesized La0.7Sr0.3MnO3 (LSMO) compound using sol-gel method and samples of crystallite size of ∼20, ∼41, and ∼49 nm were obtained by giving different heat treatment. Seebeck coefficient (α), electrical resistivity (ρ), and thermal conductivity (κ) measurements were carried out in 300–600 K temperature range. The systematic change in the values of α from ∼−19 μV/K to ∼−24 μV/K and drastic reduction in the values of κ from ∼0.88 W/mK to ∼0.23 W/mK are observed as crystallite size is reduced from 49 nm to 20 nm at ∼600 K. Also, fall in the values of ρ in the paramagnetic (PM) insulator phase (400–600 K) are effectively responsible for the increasing trend in the values of ZT at high temperature. For the crystallite size of 41 nm, the value of ZT at 600 K was found to be ∼0.017.

Effect of synthesis route on structural, magnetic and magnetocaloric aspects and critical behavior of La0.6Ca0.3Ag0.1MnO3

The La0.6Ca0.3Ag0.1MnO3 compound was elaborated using two different methods: solid state (S1) reaction and sol-gel (S2) route. Single-phase compound formation was confirmed by preliminary X-ray structural analysis and all samples crystallized in the orthorhombic system with a Pnma space group. The average crystallite size of conventionally processed sample is significantly large as compared to the Pechini sol-gel sample. The obtained results showed a paramagnetic-ferromagnetic transition in all samples. The Banerjee criterion revealed a second order magnetic transition of all samples. The compound elaborated by sol-gel reaction underwent a larger magnetocaloric effect (MCE). The exhibited large relative cooling power (RCP) of 230.35 J/Kg under 5 T indicated that the La0.6Ca0.3Ag0.1MnO3 compound is a good candidate for magnetic refrigeration application. Moreover, β and γ critical exponents were investigated through modified Arrott plots and Kouvel- Fisher (KF) according to the static magnetic measurements around the temperature transition. Also there are found to follow scaling equation with the magnetization data scaled into two different curves below and above TC, which implies the reliability and accuracy of the exponents. The critical exponents find are comparable to the values theoretical predicted for the tricritical mean-field for both samples.

Large magnetoresistance and relative cooling power in polycrystalline [formula omitted] compound

The effect of the phase boundary of ferromagnetic metallic and ferromagnetic insulator state (FMM-FMI) on magnetotransport and magnetocaloric properties in the Pr0.775Sr0.225MnO3 compound has been described in this study. An enhancement of magnetoresistance (MR) has been observed in the Pr0.775Sr0.225MnO3 compound compared to the compounds, reside on both sides of the phase boundary (i.e. FMI and FMM phases for Sr doping 0.2 and 0.3 respectively in Pr1-xSrxMnO3). Moreover, a large relative cooling power (RCP), an important parameter for utilization of magnetocaloric materials, has also been achieved in this compound. The large value of RCP has been attributed to the formation of ferromagnetic clusters, formed above the ferromagnetic ordering temperature (T>TC). On the other hand, enhancement of MR is achieved because of the suppression of enhanced phase fluctuations, arises due to the closeness of FMM-FMI phases.

Magnetic and magnetocaloric properties in polycrystalline La0.2Gd0.5Ba0.3MnO3 compound

The detail magnetic measurements of the polycrystalline La0.2Gd0.5Ba0.3MnO3 (LGBMO) compound have been presented in this manuscript. The compound shows high value of magnetocaloric effect (MCE) (-ΔS=9.1J/kg-K at 12 K) at low temperature. The experimental results of magnetization and magnetic memory effect confirm the existence of glassy magnetic phase in the compound at the low temperature (T<35K). The rejuvenation study further substantiates the presence of glassy phase. This high value of MCE in the LGBMO compound has been addressed by the presence of the glassy phase.

Evaluation of La0.7Sr0.3Mn1-xBxO3 (B=Mo, Ti) nanoparticles synthesized via GNP method for self-controlled hyperthermia

This current work deals with the study of the magnetic and biomedical characterization of La0.7Sr0.3Mn1-xBxO3 (B=Mo, Ti) nanoparticles for hyperthermia applications. Our nanoparticles were prepared through an aqueous combustion process (Glycine Nitrate Process, GNP), and are characterized with a mean crystallite size about 18 nm.The incorporation of Ti4+ and Mo6+ in Mn-site induced a structural transition from rhombohedral structure with R-3 C space group for La0.7Sr0.3MnO3 compound to orthorhombic one with Pnma space group for La0.7Sr0.3Mn0.95Mo0.05O3 and La0.7Sr0.3Mn0.95Ti0.05O3 compounds. The morphological properties indicated a variation in grain size ranging from 82 to 90 nm with doping extra element in manganese site. All samples exhibit a classical behavior from ferromagnetic (FM) to paramagnetic (PM) state as the temperature increases. A decrease in Curie temperature (TC) has been remarked from 84 °C to 70 °C and 82 °C for La0.7Sr0.3MnO3, La0.7Sr0.3Mn0.95Ti0.05O3, La0.7Sr0.3Mn0.95Mo0.05O3 respectively. According to the Arrott plots, the slopes of the curves of all the samples are positive, which is a signature of second order transition.The magnetic heating characteristics in AC field were measured in alternating magnetic fields of 23.89 mT at a fixed frequency of 518.7 kHz. The intrinsic loss power (ILP) has been calculated from SAR values. The different nanoparticles with a high ILP may be useful for the in situ hyperthermia treatment of cancer cells.