O3 Manganites Research Articles

Effect of La3+ Substitution at Bi-Site on Transport Properties of Bi0.3-xLaxPr0.3Ca0.4Mn0.1Cr0.9MnO3

Magnetic and electronic transport properties of Bi0.3-xLaxPr0.3Ca0.4Mn0.1Cr0.9O3 (0≤x≤0.2) manganites have been investigated by measurements of AC-susceptibility, resistivity and magnetoresistance. The samples were prepared using conventional solid-state synthesis method. Magnetic susceptibility versus temperature measurements showed all samples exhibit ferromagnetic to paramagnetic transition with Curie temperature, Tc enhanced from 111 K (x=0) to 174 K (x=0.2). Electrical resistivity measurements of the samples in zero field showed increase of metal-insulator (MI) transition temperature from 58 K(x=0) to 88 K(x=0.2). The increase in both Tc and TMI indicates enhancement of double exchange (DE) interaction involving Mn3+ and Mn4+ ions as a result of weakening of the hybridization effect between Bi3+ 6s2 lone pair with O orbital due to La3+ substitution. La substitution in the Bi-based compound is suggested reduce MnO6 octahedral distortion hence increasing delocalization of charge carriers. The observed variation in MR behavior due to La substitution indicates the substitution influence the MR mechanism of extrinsic and intrinsic behavior in Bi0.3-xLaxPr0.3Ca0.4Mn0.1Cr0.9O3 .Â

Long-range ferromagnetic ordering in La0.7Sr0.3Mn0.9Cu0.1O3 manganite

Nanosized La0.7Sr0.3Mn0.9Cu0.1O3 manganite was synthesized via the sol–gel procedures. The structural, morphological, magnetic and magnetocaloric properties as well as the critical phenomena were investigated. The sample was described by X-ray diffraction (XRD) technique at room temperature which confirms the single phase with a rhombohedral structure belonging to the R$$\overline{3}$$c space group. The magnetic measurements indicated the presence of a second-order ferromagnetic–paramagnetic phase transition at 320 K. According to hysteresis cycles, at 10 K a typical soft FM behavior with a low coercive field was observed. The critical exponents values (β, γ, and δ) as well as the Curie temperature TC were determined using different approaches such as the extrapolation of Arrott plots, Kouvel–Fisher (KF) method and critical isotherm analysis. The critical parameters values (β = 0.489 ± 0.003 with TC = 323.41 K ± 0.23, γ = 1.014 ± 0.020 with TC = 324.32 K ± 0.48 and δ = 3.074) are located near those theoretically predicted by mean-field theory, indicating the long-range ferromagnetic coupling in this system. The reliability of these critical parameters was confirmed by both the universal scaling hypothesis and the Widom scaling relation. Additionally, to estimate the spontaneous magnetization MS (T), we used a process which depends on the analysis of the magnetic entropy change (− ΔSM). A satisfactory agreement was found between the values of the spontaneous magnetization determined from the entropy change ((− ΔSM) vs. M2) and those obtained from the extrapolation of the Arrott curves (μ0H/M vs. M2).

Influence of sintering temperature on the structure and electrical transport properties of La0.7Ba0.1Sr0.2Mn0.85Cu0.15O3 manganites

A systematic study of the La0.7Ba0.1Sr0.2Mn0.85Cu0.15O3 manganites have been conducted, mainly to understand the influence of sintering temperature on structure, microstructure, and electrical transport properties in the materials. Polycrystalline sample of La0.7Ba0.1Sr0.2Mn0.85Cu0.15O3 were prepared using sol-gel method and sintered at 1100 °C and 1200 °C. X-ray diffraction result shows that sintering temperature does not affect the crystal structure of the materials which remain rhombohedral with R-3c space group. a more detailed examination shows that sintering temperature change the unit cell volume, <Mn-O-Mn> bond length, and <Mn-O> bond angle of the samples. The electrical resistivity decreases followed by the decrease in the grain size with the increase in sintering temperature. Analysis using theoretical model shows that both samples can be well explained using percolation model. Fitting result suggests that the transport properties of the materials at low temperature were governed by the scattering and interaction between electron, phonon, and magnon. At high temperature, the electrical transport of the samples was governed by the hopping of polarons.

Sintering Temperature Effects on Structural, Magnetic, Magnetocaloric and Critical Properties of Nd0.67Pb0.33Mn0.9Al0.1O3 Manganites

We have reported the results of structural, magnetic, and magnetocaloric characterizations as well as the critical behaviors of the polycrystalline Nd0.67Pb0.33Mn0.9Al0.1O3 manganites. These samples, denoted as S900 and S1100, were prepared using the sol–gel method and sintered separately at 900 °C and 1100 °C, respectively. XRD analysis shows good crystallization for the samples in the $$ R\overline{3}c $$ rhombohedral structure. From M(T) curves, second-order ferromagnetic–paramagnetic (FM–PM) phase transitions appear at the Curie temperatures (TC) around 130 K and 155 K for S900 and S1100, respectively. The estimated values of magnetic entropy change (−ΔSm) at μ0H = 5 T were found to be 3.23 and 4.41 J/kg.K for S900 and S1100, respectively. The corresponding values of relative cooling power (RCP) are equal to 242 and 245 J/kg. These values are relatively higher, making our samples promising candidates for magnetic refrigeration technology. We found that the critical exponents (β, γ, and δ) agree well with those of the mean-field and the 3D-Heisenberg models for S900 and S1100, respectively.

Magnetic phase transition in La0.8Sr0.2Mn0.9Sb0.1O3 manganite under pressure

The high-pressure evolution of structural and magnetic properties of the single valence Mn3+ manganite La0.8Sr0.2Mn0.9Sb0.1O3 was studied by means of neutron powder diffraction up to 4.5 GPa in the temperature range of 10–300 K. At ambient pressure, a ferromagnetic ground state with the magnetic ordering temperature TC ≈ 175 K is stabilized. Application of high pressure suppresses the initial FM phase and leads to the appearance of a new A-type antiferromagnetic AFM phase with TN ~ 130 K at P = 2.2 GPa. Under compression, both TC and TN almost linearly increases with the pressure coefficient of 1.9(2) and 0.9(3) K/GPa, respectively. It is assumed that the appearance of the A-type AFM state is mediated by the strong anisotropic distortions of MnO6 octahedra, coupled to the egdx2-z2 orbital polarization at high pressures.

Effect of A-site-substitution on structural, magnetic and magnetocaloric properties in La0.7Sr0.3 Mn0.9Cu0.1O3 manganite

Abstract The effect of bismuth and calcium substitution on the structure, magnetic and magnetocaloric properties in La0.7Sr0.3Mn0.9Cu0.1O3 manganite compounds were investigated. All the samples were synthesized using the conventional sol-gel route. The structural analysis revealed that our compounds crystalize in the rhombohedral structure ( R 3 - c space group), at room temperature. The magnetic measurements showed that all the studied compounds exhibited a second order paramagnetic (PM)-ferromagnetic (FM) transition at Curie temperature TC ranging between 290 and 320 K. The magnetic entropy change ( - Δ S M ) values estimated by the Landau theory are very close to those obtained using the classical Maxwell relation. Under an applied field μ0H = 5 T, the maximum of the magnetic entropy change ( - Δ S M max ) and the relative cooling power (RCP) are found to be 3.06 J/kg.K and 198 J/kg for La0.7Sr0.3Mn0.9Cu0.1O3, 3.39 J/kg.K and 161 J/kg for La0.6Bi0.1Sr0.3Mn0.9Cu0.1O3, and 3.65 J/kg.K and 184 J/kg for La0.6Bi0.1Sr0.25Ca0.05Mn0.9Cu0.1O3. These obtained values were compared with those of some other reported manganite and showed that our compounds could be as promising candidates for magnetic refrigeration.

Comparative study of La0.6R0.1Ca0.3Mn0.9Cr0.1O3 (R = La, Eu and Ho) nanoparticles: effect of A-cation size and sintering temperature

A systematic study of nanocrystalline La0.6R0.1Ca0.3Mn0.9Cr0.1O3 (R = La, Eu and Ho) manganites has been undertaken to analyse the effect of sintering temperature and A-site cation radius on the structural and magnetic properties. In order to acquire a series of samples with different particle sizes, the samples were prepared by a solution combustion method and were subjected to annealing at four different temperatures. Rietveld analysis of X-ray diffraction (XRD) data confirmed the presence of orthorhombic symmetry with Pbnm space group for all the samples. The grain size retrieved from the TEM analysis is greater than the noted crystallite size calculated from XRD by the Scherrer’s equation. A paramagnetic-ferromagnetic transition is shown by all our investigated compounds at low temperature. With increasing sintering temperature or particle size, the Curie temperature (Tc) was found to increase, which is attributed to the magnetically disordered surface layer. All the phases obey Curie–Weiss law in the high temperature region and the effective magnetic moment calculated from the high temperature paramagnetic region shows an increase with sintering temperature.

Study of mean-field theory on the magnetocaloric effect of La0.7Bi0.05Sr0.15Ca0.1Mn0.85In0.15O3 manganite

In this paper, we study the molecular field model to analyze the magnetocaloric effect (MCE) and the magnetic properties of La0.7Bi0.05Sr0.15Ca0.1Mn0.85In0.15O3 perovskite. This typical numerical theory was used to modulate the experimental data. The mean-field exchange parameter λ, the order of phase transition and the Brillouin function were immediately studied. The MCE has been obtained with the thermodynamics of the model. A good agreement between the theoretical and experimental data has been observed. From the Landau theory, it has been successfully verified that the nature of transition is of second order.

Glow discharge effect on temperature and time of treatment for the synthesis of Mo-doped manganite

We report the synthesis of CaMn0.9Mo0.1O3 manganite by glow discharge (GD) plasma treatment under Argon-Air atmosphere. The morphological, structural and magnetic properties were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and magnetization measures. The results from these measures reveal that the properties of GD synthesized manganite are similar to that exhibited by CaMn0.9Mo0.1O3 produced by conventional resistive furnace. The Rietveld analysis of XRD patterns performed at room temperature show that the samples crystallize in orthorhombic structure of Pnma (62) space group. The magnetization curves as a functionof temperature show two inflection points related to paramagnetic-antiferromagnetic and structural transition. The GD treatment produces a compound with similar properties, reducing the time and energy consumption in comparison with conventional synthesis route by using resistive furnace.

Compact Manganite-Graphene Magnetoresistive Sensor

A magnetic field sensor based on a manganite/Al 2 O 3 -substrate/three-layer graphene structure operating in the range of 0.1-20 T was designed and fabricated. The La 0.9 Sr 0.1 Mn 1.2 O 3 (LSMO) manganite film and graphene layers were prepared on the opposite sides of polycrystalline Al 2 O 3 substrate, which enabled scaling of the effective volume of the device to about 0.16 mm 3 . The combination of two materials-graphene with positive magnetoresistance (MR) and manganite with negative MR-led to a significant increase of the response signal and sensitivity compared with individual graphene or manganite sensors. This was achieved by increasing the MR of the individual manganite and graphene elements. The MR of LSMO was increased by using pulsed-injection metal-organic chemical vapor deposition based on two precursor sources with tunable vapor supersaturation and growth rate. The MR of three-layer graphene was optimized by changing the width/length ratio of the rectangular planar configuration and scaling the dimensions from millimeters to few hundred micrometers. The result was a maximal sensitivity of 72 mV/VT in the field range of 1-3 T.

Structural, electrical, dielectric properties and conduction mechanism of sol-gel prepared Pr0.75Bi0.05Sr0.1Ba0.1Mn0.98Ti0.02O3 compound

A detailed investigation of structural, electrical and dielectric properties of Pr0.75Bi0.05Sr0.1Ba0.1Mn0.98Ti0.02O3 manganite prepared by the sol-gel method was undertaken. The Rietveld refinement of X-ray diffraction pattern reveals that this compound is indexed in the orthorhombic structure with Pbnm space group. Structural properties are also analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy at room temperature. DC conductivity (σDC) data show the presence of a semiconductor-metal transition at TSM = 360 K. σDC is described by small polaron hopping model at high temperatures and variable range hopping model at low temperatures. AC conductivity results follow the universal Jonsher's power law at relatively low temperatures and Drude's model at high temperatures. The impedance plots display the contribution of both intra- and inter-granular contributions. Dielectric measurements exhibit highly remarkable dielectric permittivities useful in electronic devices. Dielectric losses are shown to be governed by the DC conduction mechanism and described by the Giuntini theory.

A large magnetocaloric effect of La0.8Na0.2Mn0.97Bi0.03O3 manganite synthesized by pechini Sol-Gel method and compared to the sample synthesized by solid-state route

Abstract In this work, the physical properties of the compounds La0.8Na0.2Mn0.97Bi0.03O3 prepared by solid-state (S1) and Sol-Gel (S2) methods are compared. Both compounds were found to crystallize in the rhombohedra structure with R-3c space group. They also exhibited a Ferromagnetic (FM)-Paramagnetic (PM) phase transition around the Curie temperature (TC). Curie temperature TC and magnetization decreased with the decrease of the crystallite size. The maximum of the magnetic entropy change ΔSM at 5 T, were about 4.73 J·K−1·kg−1 and 5.88 J·K−1·kg−1 for S1 and S2, respectively. We proved the second order character via the normalization curves and through the Banerjee criteria. Moreover, we determined the critical exponents values of β, γ and δ with the extrapolation of Arrott plots, the Kouvel fisher technique and the critical isotherm, respectively. The validity of the exponents values was confirmed with the scaling hypothesis; the M (T, e) curves collapsed onto two independent universal branches below and above Tc.

Impedance studies of La0.6Gd0.1Sr0.3Mn0.9In0.1O3 manganite prepared by the sol-gel method

A systematic study of complex impedance analysis and dielectric properties of La0.6Gd0.1Sr0.3Mn0.9In0.1O3manganite are carried out. Our sample is prepared using the sol-gel method. The impedance spectrum analysis was fitted by adequate equivalent circuits involving the contributions of grain and grain boundaries in the conduction mechanism. The imaginary part of the complex impedance (Z″) frequency dependence revealed one relaxation peak. The dielectric constant shows a normal behavior. The real part (ε′) and loss tangent have been explained on the basis of space charge polarization according to Maxwell-Wagner's two layer model and Koops phenomenological theory. The conductivity curves have been investigated by the Jonscher universal power law: σ=σAC+σDC. The conduction process is found to be dominated by a thermally activated small polaron hopping (SPH) model.

Magnetotransport properties and phase separation in iron substituted lanthanum-calcium manganite

Crystal and magnetic structure of iron substituted La0.7Ca0.3Mn0.5Fe0.5O3 manganite was investigated by powder neutron diffraction in the 10–300 К temperature range. It is established that the unit cell parameters at 300 K are a = 5.447(2) Å, b = 7.709(3) Å, c = 5.467(3) Å and they change vs. temperature with rates da/dT ∼ 1.3*10–4 Å*K−1, db/dT ∼ 1.7*10–4 Å*K−1 and dc/dT ∼ 1.6*10–4 Å*K−1, respectively. It was also realized the measurements of magnetization and electrical resistivity in the 5–300 K temperature range including in magnetic fields up to 1 T. Magnetic phase separation was observed. Upon the field increase the glass, Tg, and irreversibility, Tirr, temperatures decrease, while the magnetic ordering temperature, Tmo, increases. Upon the temperature increase both the residual magnetization, Mr, and coercive field, Hc, decrease. A complex frustrated magnetic state in which the long-range G-type antiferromagnetic phase coexists with the short-range ferromagnetic clusters was established. An average size of ferromagnetic clusters is Dav ∼ 20 nm. An anomalous temperature behavior of electrical conductivity for La0.7Ca0.3Mn0.5Fe0.5O3 was found which confirms a transformation of various magnetic states. Different models of conduction mechanism were considered. The origin of the unusual magnetic state, the electrical conduction mechanisms, and the relationship between magnetic and electrotransport properties in this sample were discussed.

Investigation of structural, electrical and dielectric properties of sol-gel prepared La0.67-xEuxBa0.33Mn0.85Fe0.15O3 (x=0.0, 0.1) manganites

Polycrystalline samples of La0.67-xEuxBa0.33Mn0.85Fe0.15O3 (x = 0.0, 0.1) manganites have been prepared using sol-gel route. Structural characterizations of our materials were performed by powder X-ray diffraction, Scanning Electron Microscopy and by Energy Dispersive X-ray spectroscopy at room temperature. Our samples are single phase and crystallize in the orthorhombic structure with the Pbnm space group. Electrical and dielectric properties of La0.67-xEuxBa0.33Mn0.85Fe0.15O3 (x = 0.0, 0.1) compounds have been studied using impedance spectroscopy technique in the temperature range from 80 to 400 K and the frequency range from 40 to 107 Hz. DC measurements show that the studied structures exhibit semiconductor (SC) behaviour in all temperature range of study. AC data analysis show a transition from SC to metallic behaviour at 160<TSM<170 K and 220<TSM<240 K for x = 0 and 0.1 respectively. In the SC region, the conductivity σAC obeys to Jonsher power law at low temperatures while at high temperatures, the classical Drude model describes well the frequency dependence of the conductivity data. Nyquist plots allow us to propose an equivalent circuit involving the contribution of grains and grain boundary elements. Dielectric measurements show that the dielectric relaxation is governed by the DC conduction process. Dielectric results confirm the high values of the permittivity which approve the use of manganites in electronic applications. Besides, the relaxation process in the dielectric spectra is shown to be totally obscured by the DC-conductivity.

Magnetocaloric Effect in La0.67Ba0.33Mn0.95Ni0.05O3 Manganite Near Room Temperature

We report the structural, magnetic, and magnetocaloric properties of La0.67Ba0.33Mn0.95Ni0.05O3 (LBMNO) manganite, synthesized by sol-gel method. X-ray diffraction (XRD) analysis using Rietveld refinement showed that this sample crystallizes in the rhombohedral structure with R $\bar {3}$ c space group. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analysis were used to confirm the structure formation of the LBMNO material. The temperature dependent magnetization data revealed a transition from ferromagnetic (FM) to paramagnetic (PM) phase at $T_{\mathrm {C}}=$ 308 K. Using Arrott plots, it was found that the transition is of a second order. From the measured magnetization data as a function of magnetic applied field, the magnetic entropy change (−ΔSM) and the relative cooling power RCP have been determined. In the vicinity of $T_{\mathrm {C}}$ (−ΔSM) reached a maximum value of 2.15 J kg− 1 K− 1 and a large RCP value of about 299 J kg− 1 under 5 T− 1. This magnetocaloric effect has been analyzed by considering the Landau theory of magnetic phase transition. Consequently, our sample can be considered a promising material in room-temperature magnetic refrigeration.

High dielectric constant and relaxor behavior in La0.7Sr0.25Na0.05Mn0.8Ti0.2O3 manganite

The dielectric properties of La0.7Sr0.25Na0.05Mn0.8Ti0.2O3 (LSNMTi0.2) were investigated as a function of temperature and frequency. Compared with the dielectric constants of most ferroelectric and relaxor materials, in this compound we have found a colossal dielectric constant phenomenon consisting in a low frequency dielectric constant ε″ over 106 around room temperature. However, Frequency and temperature dependent ac conductivity and complex impedance studies were linked to semiconducting grains and insulating grain boundaries, which support the non-Debye type of relaxation in the polycrystalline sample. Furthermore, decrease in the resistive properties with an increase in temperature, explained in terms of the mobility of the charge carriers, signaled the semi-conductor behavior with negative temperature coefficient of resistance (NTCR). The scaling behavior of the Modulus spectra M″ versus frequency allowed us to understand whether the short-range or the long-range movement of charge carriers is the dominant in relaxation process, confirming the non-Debye type of multiple relaxations in the system. The variation in the dielectric permittivity, explained in terms of the space charge polarization according to the Maxwell–Wagner model and the Koop's phenomenological theory and the large dielectric response, was induced by the barrier layers in the grain boundaries and the mixed-valent structures of Mn3+/Mn4+ and Ti4+/Ti3+.

Investigation of charge transport mechanism in semiconducting La0.5Ca0.5Mn0.5Fe0.5O3 manganite prepared by sol–gel method

Here in, we report the charge transport mechanism in semiconducting La0.5Ca0.5Mn0.5Fe0.5O3 (LCMFO) polycrystalline material synthesized via sol–gel auto combustion route. X-ray diffraction (XRD) analysis confirmed the orthorhombic phase of the prepared material. Temperature dependent resistivity and impedance spectroscopy measurements have been carried out to probe the dielectric and electrical conduction mechanism which revealed a change of Mott variable range to the small polaronic hopping conduction mechanism around 303 K. The complex impedance and modulus spectra undoubtedly showed the contribution of both grain and grain boundary effect on the conduction properties of LCMFO. An equivalent circuit [(RgbQgb) (RgQg)] model has been used to address the electrical parameters associated with the different phases (grains and grain boundaries) having different relaxation times. The values of resistances of two phases obtained after fitting the equivalent circuit in the nyquist plot have been analyzed which confirmed the change of conduction mechanism around 303 K. The resultant change in conduction mechanism is also supported by the conductivity plots.

Ferromagnetic ordering, magnetic and magnetotransport properties of R1−xSrx(Mn1−x/2Sbx/2)O3 (R = La, Pr, Nd, Sm, Eu) manganites

Neutron diffraction, magnetic and magnetotransport studies of perovskites ( )O3 (R = La, Pr) were carried out. It is shown that for x ∼ 0.2 systems undergo a transition from an antiferromagnetic state (x = 0) to a ferromagnetic state. In the case of the R = La series a structural transformation from the O′-orthorhombic phase (x = 0) to the O-orthorhombic one occurs, which is due to orbital disordering. At x ≥ 0.6 cluster spin glass like phases arise due to the competition between antiferromagnetic and ferromagnetic interactions, as well as due to the strong diamagnetic dilution. In case of the R = Pr series the structural transition into the O-orthorhombic phase was not observed under (Sr, Sb) codoping. As the ionic radius of the rare-earth ion decreases in the series R0.7Sr0.3Mn0.85Sb0.15O3 the crystal structure distortion increases and the ferromagnetic state (R = La, Pr, Nd) is gradually transformed into a spin glass like state (R = Sm, Eu). The ferromagnetic compounds are insulators and exhibit a large magnitude of the magnetoresistance apparently associated with very small amount of Mn4+ ions. The covalent component of the chemical bond and e.g.-orbitals disordering/mixing are assumed to be responsible for ferromagnetism in the compounds under study.

Effect of Fe doping on structure, magnetic and electrical properties La0.7Ca0.3Mn0.5Fe0.5O3 manganite

The crystal and magnetic structures of La0.7Ca0.3Mn0.5Fe0.5O3 compound have been studied by neutron powder diffraction in the temperature range of 10–300 К. The magnetization and electrical resistivity measurements have been also performed in the temperature range of 5–300 K in magnetic fields up to 1 T. These experimental results indicate a formation of a complex magnetic state in which the long-range antiferromagnetic G-type phase coexists with the short-range ferromagnetic clusters. The electrical conductivity of La0.7Ca0.3Mn0.5Fe0.5O3 demonstrates an anomalous temperature behavior suggesting a switching between different states. The origin of the unconventional magnetic state, the mechanisms of the electrical conductivity, and correlation between magnetic and transport properties in this manganite have been discussed.