MnO3 Perovskite Manganite Research Articles

Influence of heat sintering on the physical properties of bulk La0.67Ca0.33MnO3 perovskite manganite: role of oxygen in tuning the magnetocaloric response.

The effect of heat treatments on bulk poly-crystalline La0.67Ca0.33MnO3 perovskite manganite is presented, to explore the possible enhancement in magnetocaloric performance. Samples were prepared via conventional solid-state reaction route with annealing and sintering at various temperatures. Detailed measurements of temperature-dependent and field-dependent magnetization were carried out to estimate the Curie point and order of magnetic transition. The increased sintering temperature results in a steep transition near the TC, and establishes the magnetic sensitivity as well as the active zone for substantial magnetocaloric performance, at about 168.2% for the LCM9 (sintered at 900 °C) sample. The cause for the significant improvement in the magnetic and magnetocaloric response is brought to light using detailed X-ray photoelectron spectroscopy (XPS) analysis, highlighting the role of oxygen in modifying the Mn3+/Mn4+ charge ratio. The maximum value of the isothermal magnetic entropy change for the optimized sample is found to be 6.4 J kg-1 K-1, achieved at 269 K, while temperature-averaged entropy change (TEC) values, TEC(ΔTH-C = 3 K) and TEC(ΔTH-C = 5 K), of 6 J kg-1 K-1 and 5.2 J kg-1 K-1, respectively, were obtained with a low magnetic field change of 20 kOe. The obtained isothermal entropy change at low field for the optimized La0.67Ca0.33MnO3 sample is higher than that of pure Gd and most oxide-based materials. The relative cooling power (RCP) value is around 93 J kg-1 (ΔH = 20 kOe). The order of the phase transition is examined with universal scaling; the scaled entropy change curves confirm the collapse onto a single curve for LCM9, asserting second-order character, whereas the breakdown of the curve with a dispersion relation (d) of 101.1% at Θ = -5 confirms the onset of intrinsic first-order nature in the case of the high-temperature-sintered samples. Calorimetry measurements show thermal hysteresis of 2.4 K and 7.1 K for LCM11 (sintered at 1100 °C) at ramp rates of 5 K min-1 and 10 K min-1, respectively, confirming the first-order nature of the magnetic transition.

Investigation of crystal structural and magnetic properties of titanium doped Pr0.67Ba0.33MnO3 perovskite manganites

Pr0.67Ba0.33Mn1-xTixO3 (x = 0 and 0.02) were synthesized using a conventional solid-state synthesis method to investigate the effect of Ti substitution on their magnetic and electrical transport properties. All the samples were structurally evaluated by XRD diffraction Rietveld refinement method which showed an increase in unit cell volume with increasing Ni content, indicating that Ti is partially substituted at Mn. Scanning electron microscopy (SEM) and energy dispersive X-tray (EDX) are used to examine the surface morphology and identified elements in the samples' compounds. Fourier transform infrared spectroscopy (FTIR) reveals that all the samples exhibit a transmission band in the range of 590 cm-1 - 610 cm-1 . For x = 0, magnetization measurements showed paramagnetic (PM) to ferromagnetic (FM) transition at the transition temperature, TC ∼ 213 K. For Ti-substituted samples, ferromagnetic (FM) to PM transition was reduced with Curie temperature (TC), decreasing from 213 K (x = 0) to 205 K (x = 0.02). On the other hand, the M(H) showed the presence of a linear graph for x = 0 and x = 0.02 which may be related to the presence of paramagnetic at room temperature.

Structural, magnetic, magnetocaloric and critical studies of Sm-substituted La0.67-xSmxPb0.13Ca0.2MnO3 perovskite manganites

The structural, magnetic, magnetocaloric, and critical behaviors for Sm substituted La0.67-xSmxPb0.13Ca0.2MnO3 manganites with x = 0, 0.1, and 0.2 were investigated in this work. Based on Rietveld refinement of XRD patterns, all samples have an orthorhombic structure with the Pnma space group. With Sm substitution, the average ionic radii of A-site cation (<rA>), the unit cell volume (V), the Goldschmidt tolerance factor (tG), and the average <θMn-O-Mn> bond angle decrease. Whereas the average bond distance, <dMn-O>, and the variance disorder parameter (σ2) increase. Ferromagnetic (FM) to paramagnetic (PM) phase transitions with second-order type were revealed for all samples from magnetization measurements and Arrott plots. Curie temperature (TC) decreases with Sm substitution from 298 K for x = 0–256 K for x = 0.2. Large maximum entropy change and relative cooling power (6.20 J Kg−1 K−1 and 236 J Kg−1, respectively) have been observed for the undoped sample (x = 0), but the values of these parameters are suppressed due to the disorder caused by Sm doping. The estimated critical exponents (β, γ, and δ) for the x = 0 sample are consistent with tricritical mean-field theory. However, for x = 0.1 and 0.2, they are close to the 3D- Ising model. The change in this universality class can be associated with the increase of disorder by substituting the Sm3+ cations in La0.67-xSmxPb0.13Ca0.2MnO3 manganites.

Structural and Morphology Changes in PrMnO3 Manganite Induced by Ba (x=0.33) Doping

In this paper, we discuss the structural and morphology properties of the solid-state prepared Pr0.67Ba0.33MnO3 perovskite manganite X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analyses were utilised to examine the structure, morphology, and chemical composition. The compound exhibits a single phase with an orthorhombic perovskite structure with a Pnma space group without any impurities. The refined cell parameters are a = 5.504 Å, b = 7.778 Å, and c = 5.528 Å (α = β = γ = 90° and a ≠ b ≠ c), therefore the cell volume is 236.723 Å^3. The tolerance factor is used to predict the stability of the Pr0.67Ba0.33MnO3, which is τ = 0.9241. Fourier transform infrared spectroscopy (FTIR) reveals that the Mn-O bonds appear at 600 cm^(-1). In addition, morphology SEM revealed that the grain sizes are heterogeneous, and the grain shapes are irregular. Using EDX technique, the percentage elemental composition of Pr, Ba, Mn, and O was determined. The values of the atomic percentages for each element are almost identical to the ratios of the elements during sample preparation.

Quenching of spin-orbit coupling and signature of Griffiths Phase in nanocrystalline La0.6Ba0.4MnO3 perovskite manganite

The size-dependent structural and magnetic properties of nano and bulk samples of 40 ​mol% Ba2+-doped LaMnO3 (i.e., La0.6Ba0.4MnO3) manganite have been investigated in detail. The Rietveld refinement of X-ray diffraction data confirms that nano and bulk La0.6Ba0.4MnO3 manganites crystallize into ideal cubic perovskite structure with Pm3¯m space group. The refined unit cell parameters decrease with increasing calcinations temperature or particle size. The temperature dependent magnetization measurements reveal that both the bulk and nano samples exhibit paramagnetic (PM) to ferromagnetic (FM) phase transition at Curie temperature (TC). A distinct bifurcation between magnetization curves under zero-field cooled (MZFC) and field-cooled (MFC) measurements reveals the possible existence of frustrated magnetic ordering or spin glass clusters. For nano sample, a sharp downward deviation in inverse susceptibility from Curie-Weiss law is observed, which indicates the existence of Griffiths Phase. The analysis of the field dependent magnetization M(H) curves measured at 10 ​K, in terms of saturation moments, reveals that there is a coupling between spin and orbital magnetic moments, in bulk sample of La0.6Ba0.4MnO3 manganite, which can be quenched by reducing particle size of the manganite. According to the Banerjee's criterion, nano sample exhibits first-order magnetic transition and bulk sample shows second-order magnetic transition in the low magnetic field region.

Examination of the usability of La0.67Ba0.33MnO3 perovskite manganite compound with magnetocaloric effect in magnetic cooling technology

Perovskit manganit yapılı bileşikler yüksek manyetokalorik etki (MKE) ve devesa manyetodirenç (DMD) etkileri göstermeleri nedeniyle son yıllarda oldukça yaygın olarak çalışılan malzemelerdir. ABO3 formundaki perovskit manganit bileşikleri, ideal durumda iken antiferromanyetik ve yalıtkan özellik sergilerken, A-bölgesine yapılan +1 ve/veya +2 değerlikli element katkısı ile ferromanyetik ve iletken özellik göstermektedir. Perovskit manganit bileşikler elektriksel ve manyetik özelliklerini katkılamalar ile değiştirilebilir ve yığın olarak kolayca üretilerek şekillendirilebilir olmasının yanında, gösterdikleri yüksek MKE nedeniyle yeni tip soğutucu elemanı olarak manyetik soğutma (MS) sistemlerinde etkin olarak kullanılacak yeni tip malzeme olma özelliği taşımaktadır. Bu çalışmada, alaşımlar yerine daha ucuza mal edilen ve şekillendirilmesi kolay olan perovskit manganit bileşiği ele alınmıştır. İdeal durumdaki LaMnO3 perovskit manganit bileşiğinde La eksiltilerek yerine %33 (1/3) oranında Ba katkılanmıştır. Ba katkılanan La0.67Ba0.33MnO3 bileşiği sol-jel metodu kullanılarak üretilmiş ve yığın olarak elde edilmiştir. Daha sonra örnek 1000oC’de 24 saat ısıl işleme tabi tutulmuş, yapısal ve manyetik özellikleri incelenmiştir. Perovskit manganit bileşiğin X-ışınları kırınım deseni üzerinden yapılan arıtım sonucunda bileşiğin kübik yapıda olduğu tespit edilmiş ve Pm3m uzay grubuna ait olduğu bulunmuştur. SEM analizlerinden tane boyutunun 100-200 nm aralığında değiştiği gözlenmiştir. Sıcaklığa bağlı yapılan mıknatıslanma ölçümlerinden La0.67Ba0.33MnO3 perovskit manganit bileşiğinin Curie geçiş sıcaklık (TC) değeri 341 K, 1 T manyetik alan altında hesaplanan manyetik entropi (-ΔSM) değeri 0.87 Jkg/K ve manyetik soğutucu malzeme olarak kullanılabilirliğini gösteren göreli soğutma gücü (RCP) değeri 38 J/kg olarak hesaplamıştır.

Elemental analysis and the impact of Sr substitution on magnetic properties of Nd(1-x)Sr(x)MnO3 (x = 0; 0.5 and 1) perovskite manganite

The series sample of Nd(1-x)Sr(x)MnO3 (x = 0; 0.5 and 0.1) has been prepared with sol-gel method. The elemental compound or chemical characterization of Nd(1-x)Sr(x)MnO3 (x = 0; 0.5 and 0.1) were obtain using Energy Dispersive X-Ray Spectroscopy (EDS). The EDS results show that the elements were all presents in the sample, which also verified that the sample has successfully synthesized. The Vibrating Sample Magnetometer (VSM) was used to measure the magnetic properties of the sample under room temperature. The results show that the material is all soft magnetic with the magnetization decrease as the temperature decrease.

Thermal stability of the crystallographic structure of nanocrystalline Nd0.7Sr0.3MnO3 manganite with enhanced magnetic properties

We report the effect of temperature on the crystallographic structure and magnetic properties of ultrasonically prepared nanostructured Nd0.7Sr0.3MnO3 perovskite manganite. The crystal structure of as-synthesized nanoparticles remains unaltered over a wide scanning temperature range. Temperature dependent magnetization measurements demonstrate that the Curie temperature (Tc) of Nd0.7Sr0.3MnO3 nanoparticles is in the range of 211 K–220 K under largely varying applied magnetic fields. Below Tc, the soft ferromagnetic nature of these nanoparticles is confirmed by the field-dependent magnetization measurements. The absence of the charge-ordered state is also revealed in this nanomanganite down to 20 K, which is strikingly different from analogous Nd–Sr based nanocrystals. The experimentally observed effective paramagnetic moment and saturation magnetic moment have matched quite well with the values calculated theoretically. The Tc values up to a temperature of 220 K, nearly perfect ferromagnetically ordered Mn ions below Tc, high saturation magnetization, and magnetic softness of synthesized nanostructured Nd0.7Sr0.3MnO3 manganite can be associated with their good crystallinity as well as the nominal internal and surface disorder effect owing to intermediate particle size (∼75 nm to 150 nm). Our investigation elucidates the promising potential of nanocrystalline Nd0.7Sr0.3MnO3 particles for numerous technological applications.

Magnetic phase transition, magnetocaloric and magnetotransport properties in Pr0.55Sr0.45MnO3 perovskite manganite

Herein, we report a systematic study on magnetic phase transitions, magnetocaloric and magneto-transport properties in praseodymium strontium manganite (PSMO), Pr0.55Sr0.45MnO3 synthesized using nitrate route method. The structure and phase formation were checked by Rietveld refinement of powder X-ray diffraction (XRD) at room temperature and it was found that Pr0.55Sr0.45MnO3 crystallizes in an orthorhombic structure with Pnma space group with lattice parameters a = 5.423(6) Å, b = 7.660(7) Å & c = 5.478(7) Å with cell volume V = 227.63 Å3. By analyzing the temperature and field dependence of magnetization, we find that the sample exhibits a sharp rise in magnetization below 281 K (TC) and a dip in magnetization around 182 K (TN), suggesting paramagnetic (PM) to ferromagnetic (FM) and ferromagnetic (FM) to antiferromagnetic (AFM) transition respectively at the said temperatures. The critical exponents β = 0.449(8), γ = 1.113(9) and δ = 3.476(4) for TC = 282 ± 0.5 K estimated from magnetic isotherms using modified Arrott plot follows the scaling theory. The maximum entropy change (-ΔSmaxM) and the relative cooling (RC) near PM-FM transition are found to be respectively 2.49 Jkg−1 K−1 and 112 J/kg for magnetic field 3 T proposing as potential magnetic refrigerant. The entropy behavior also suggested typical second order transition in the sample. The temperature dependence electrical resistivity shows a metal to insulator transition around 156 K at 0 T and shifts to 188 K with the application 8 T magnetic field. At 5 K, the observed magneto-resistance (MR) is 55%, a value maximum at 8 T.

Effect of sintering temperature on structure and morphology of Ca0.95La0.02Bi0.03MnO3 perovskite manganite prepared by sol-gel method

The effect of sintering temperature on the structure and morphology of Ca0.95La0.02Bi0.03MnO3 was investigated by X-ray diffraction and Scanning Electron Microscope. The sample was prepared by sol gel method. Their homogeneity was confirmed using X-ray diffraction. Rietveld refinement of X-Ray diffraction results showed that the sample sintered at 1100 °C for 12 h are single phase and have an orthorhombic structure with Pnma space group. While, the samples were sintered at 900 °C and 1000 °C did not show a single phase due to another peak is found. For the lattice parameter, crystal volume increases with increasing sintering temperature. The largest crystal volume was reached at sintering temperature 1100 °C which is equal to 208.7319 Å. For the angle of the Mn-O-Mn bond, the sample was sintered at 1100 °C has the largest value obtained 157.6695° while at 1000 °C is 157.1440° and 900 °C is 157.3655°. For the average Mn-O bond length shows relatively the same value for all sintering temperature. The sample was sintered at 1100 °C had the largest grain size. Sintering temperature does not change the crystal structure of Ca0.95La0.02Bi0.03MnO3 samples

Study of phase transition in Cu-doped La0.7Sr0.3MnO3 perovskite manganite materials by ultrasonic technique

La0.7Sr0.3Mn1−xCuxO3 perovskite manganite materials with a composition of x = 0.05, 0.10 and 0.15 were obtained using solid state reaction technique. The measurement of ultrasonic velocity over a wide range of temperature reveals the short range ferromagnetic to the antiferromagnetic transition temperature (TC) at 358, 341 and 328 K for the perovskites with the composition x = 0.05, 0.10 and 0.15 respectively. Turning of TC was achieved from 370 (x = 0) to 328 (x = 0.15) K which helps to obtain the new cathode materials for solid-oxide fuel cell.

Phase Transition of La0.62Sr0.38MnO3 Perovskite Manganites

Bulk and nano La0.62Sr0.38MnO3 perovskite manganite samples were prepared using solid state and sonochemical reaction respectively. The ultrasonic velocities measurement was made on prepared samples using ultrasonic through transmission method, at a fundamental frequency of 5 MHz over wide range of temperatures. The temperature dependence of the ultrasonic parameters shows an interesting anomaly in bulk and nano perovskite samples. The observed dramatic softening and hardening in sound velocities are related to phase transitions. Further, a decrease in grain size in the nanostructured sample leads to a shift in the ferromagnetic transition temperature (TC) from 375 to 370 K.

Transport and complex modulus study of La0.7Ca0.3MnO3 perovskite manganite nano-compound with polypyrrole as host

The paper focuses on the facile synthesis of polypyrrole/La0.7Ca0.3MnO3 perovskite magnetic nano-composites synthesized by in situ chemical oxidation method using ammonium persulfate as oxidant. The morphology and crystal phase of the prepared samples were analyzed using SEM, TEM and XRD, respectively. Electrical conductivity, dielectric constant, dielectric loss, complex electric and impedance modulus studies were invested in the frequency range of 100 Hz–5 MHz at room temperature using AC impedance analyzer. The composites show frequency dependence with relaxation mechanism. The electric and impedance modulus analysis reveals the presence of non-Debye-type relaxation process and the effect of both grain and grain boundary on the transport properties of the composites.

Transverse Relaxivity of Nanoparticle Contrast Agents for MRI: Different Magnetic Cores and Coatings

Four types of magnetic nanoparticles were synthesized, namely, the La0.65Sr0.35MnO3and La0.80Na0.20MnO3 perovskite manganites and the Mn0.61Zn0.42Fe1.97O3 and Co0.44Zn0.70Fe1.86O4 spinel ferrites. Subsequent coating with silica provided typical core–shell particles with the mean shell thickness of 14–19 nm and the mean size of cores of 49–52 nm in the case of manganites and 26–33 nm in the case of ferrites. Moreover, two other surface modifications were employed for Mn–Zn ferrite nanoparticles, specifically coating with titania, leading to larger clusters with more complex morphology, and the stabilization by citrate anions. The products were characterized by powder X-ray diffraction and transmission electron microscopy, and their magnetic properties were probed by SQUID magnetometry. The main attention was devoted to the relaxometry on aqueous suspensions of particles in a magnetic field of 0.5 T. For distinct types of the prepared core–shell nanoparticles, the temperature dependence of transverse relaxivity was measured and the role of different relaxation regimes was analyzed.

Synthesis, structure and magnetic properties of Pr0.65Ca0.3M0.05MnO3 (M = Na, K and Ag): A perovskite manganites with metamagnetic phase transitions

The synthesis, structural characterization, and magnetic properties of Pr0.65Ca0.3M0.05MnO3 (M = Na, K and Ag) perovskite manganites are reported. Our samples were synthesized using the solid state reaction method at high temperature. Rietveld refinements of the X-ray diffraction patterns show that all our samples are single phase and crystallize in the distorted orthorhombic system with Pbnm space group. The surface morphology and infrared absorption of the samples were systematically investigated. Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that the antiferromagnetic ordering temperature TAFM occurring below the charge-ordering transition temperature TCO in these narrow band manganites are slightly dependent with monovalent element. The critical magnetic field (Hc) required for metamagnetism is found to reduce drastically from 7 T for Pr0.65Ca0.35MnO3 to 2.9 T for Pr0.65Ca0.3Na0.05MnO3.

Transport Properties and Magnetoresistance of La0.8Ca0.13Ag0.07MnO3 Perovskite Manganite Synthesized by Sol-Gel Method

In this paper, we investigate the transport properties and magnetoresistance effect of La0.8Ca0.13Ag0.07MnO3 perovskite manganite synthesized by sol-gel method. The XRD pattern of the sample shows a rhombohedral perovskite structure with space group R3̄c. The EDX analysis confirms that the sample contains all expected chemical elements without any additional impurity. The temperature dependence of electrical resistivity was measured using a cryogenic magnetometer. The results show a metal-insulator transition temperature (TM-I) at 280 K. The resistivity of the sample increases with an increase of temperature below TM-I. Theoretical analyses of the temperature dependence of resistivity suggest that the resistivity due to electron-electron scattering is predominant below TI-M. The resistivity of the sample decreases when applied magnetic field 1 T at a temperature range of 10 K to 300 K. The magnetoresistance of La0.8Ca0.13Ag0.07MnO3 emanates from spin-polarized tunneling process at the grain boundary.

Structural, magnetic and magnetocaloric properties of (La1−xSmx)0.85K0.15MnO3 (x = 0.0, 0.1, 0.2 and 0.3) perovskite manganites

We have investigated effect of Sm ion substitution on structural, magnetic and magnetocaloric properties of sol-gel synthesized (La1−xSmx)0.85K0.15MnO3 (x = 0.0, 0.1, 0.2 and 0.3) perovskite manganites. X-ray diffraction analyses confirm that samples crystallize with rhombohedral symmetry in the R3̅c space group. The temperature dependence of magnetization measurements shows a clear ferromagnetic (FM)-paramagnetic (PM) phase transition with increasing temperature, and magnetic phase transition temperature (TC) decreases with increasing Sm concentration. For Sm concentrations (x = 0.0, 0.1, 0.2 and 0.3), magnetic field dependence of the maximum magnetic entropy change (−∆SMmax) are determined up to 5 T to be 7.32, 3.37, 3.28 and 2.70 J kg−1 K−1, respectively. These experimental values are also in good agreement with the calculation of the magnetic entropy change using Landau theory.

Large relative cooling power of Bi-doped La0.8−xBixSr0.08(Ca0.55Ba0.45)0.12MnO3 (x=0.0, 0.1 and 0.3) perovskites: Magnetic and magnetocaloric properties

We report magnetic and magnetocaloric properties of La0.8−xBixSr0.08(Ca0.55Ba0.45)0.12MnO3 (x=0.0, 0.1 and 0.3) perovskite manganites. Polycrystalline samples have been synthesized in air by the sol gel method at a sintering temperature of 1150°C. Powder X-ray diffraction data show that samples are phase pure and their cell parameters slightly decrease with increase in Bi content. Scanning electron micrographs show that the average particle size increases with increase in Bi content. The temperature dependent magnetization measurements show that the Curie temperatures decrease from 315K (x=0.0) to 140K (x=0.3) with increase in Bi content. The isothermal magnetization data is used to estimate the magnetic entropy changes (−ΔSM) and their calculated values are 1.12Jkg−1K−1, 1.96Jkg−1K−1 and 1.62Jkg−1K−1 for x=0.0, 0.1 and 0.3 samples respectively under an applied magnetic field of 2.0T. The corresponding values of relative cooling power (RCP) are 90Jkg−1, 180Jkg−1, 136Jkg−1 for x=0.0, 0.1 and 0.3 samples respectively. These results of magnetocaloric effect in our samples suggest that they are promising materials for the magnetic refrigeration applications.

Magnetic, magnetocaloric and critical behavior study of La0.78Pb0.22MnO3 manganite near room-temperature

We report the magnetic, magnetocaloric properties and critical behavior near transition temperature in La0.78Pb0.22MnO3 perovskite manganite, prepared by solid state reaction method. Temperature dependence of magnetization exhibits a ferromagnetic to paramagnetic transition (TC) at 292K. Close to this transition, a maximum magnetic entropy change (−ΔSMmax) of 4.31J/kg K and a relative cooling power (RCP) of 238J/K are determined at a field of 5T. Experimental results revealed that this sample underwent a second-order phase transition. Using the modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis, the critical parameters (TC, β, γ, and δ) have been determined. The estimated critical exponents (β=0.246, γ=0.929 and δ=4.49 at TC=290.01K) are found to be close to the tricritical mean-field model. These critical exponents fulfill the Widom scaling relation δ=1+γ/β, implying the reliability of our values. On the basis of the obtained critical exponents, the magnetization-field -temperature (M-μ0H-T) data around TC are found to collapse into two curves by obeying the single scaling equation M(μ0H,ε)=(ε)βf±(μ0H/εβ+γ) where ε=T−TC/TC, f+ above and f− below TC, and confirm that the obtained values of β, γ and δ are reasonably accurate and unambiguous.

Prediction of Magnetocaloric Effect in Lanthanum Deficiency with Phenomenological Model

In this paper, a profound theoretical work has been conducted on magnetic and magnetocaloric properties of La0.65−x x Ca0.35MnO3 (0 ≤ x ≤ 0.15) perovskite manganites. Our work is based on a phenomenological model. The magnetization data as a function of temperature at several magnetic fields allows to determine the magnetocaloric parameters such as the maximum of the magnetic entropy change (ΔS M), the relative cooling power (RCP), and the magnetic specific heat change (ΔC P). The theoretical predictions nearly match with the experimental measurements. These materials present large magnetocaloric effect, suggesting their possible application in moderate magnetic fields.