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Structural, magnetic and magnetocaloric properties of the nanocrystalline La 0.7 Te 0.3 Mn 0.7 Co 0.3 O 3 perovskite manganite were investigated. X-ray diffraction pattern indicated that the nanocrystalline sample crystallized in orthorhombic crystal structure with Pbnm space group. The average particle size was calculated using scanning electron microscope and it was found to be ∼150 nm. Temperature dependence magnetization measurements revealed ferromagnetic–paramagnetic phase transition and the Curie temperature (T C ) was found to be ∼201 K. Field dependence magnetization showed the hysteresis at low temperature with a coercive field of ∼0.34 T and linear dependence at high temperature corresponds to paramagnetic region. Based on the magnetic field dependence magnetization data, the maximum entropy change and relative cooling power (RCP) were estimated and the values were 1.002 J kg −1 K −1 and 90 J kg −1 for a field change of 5 T respectively. Temperature dependent resistivity ρ(T) data exhibited semiconducting-like behavior at high temperature and the electrical transport was well explained by Mott’s variable-range hopping (VRH) conduction mechanism in the temperature range of 250 K–300 K. Using the VRH fit, the calculated hoping distance (R h ) at 300 K was 54.4 Å and density of states N(E F ) at room temperature was 7.04 × 10 18 eV −1 cm −3 . These values were comparable to other semiconducting oxides. [ABSTRACT FROM AUTHOR]

The ferroelectric, leakage, dielectric, and energy storage properties of lead‐free Na0.5K0.5NbO3/BiMnO3 (KNN/BMO) solid‐solution films are investigated. The strong ferroelectric relaxation behaviors of slim ferroelectricity with small remanent polarization and coercive field induce a high energy‐storage density and efficiency at room temperature. The energy density reaches 14.8 J cm−3, even the efficiency is up to 79.79% under the applied electric field of 985.66 kV cm−1. Moreover, the energy storage performances of KNN/BMO solid‐solution films exhibit good thermal stability over a wide temperature range and high ferroelectric fatigue endurance after switching 106 bipole electrical cycles. KNN/BMO solid‐solution films can replace lead‐based films and other outstanding lead‐free systems in the energy storage performance. [ABSTRACT FROM AUTHOR]

LaCaMnNiO (0 ≤ x ≤ 0.3) is synthesized by solid-state reaction at low temperatures, followed by calcination in air. The precursor and its calcined products are characterized by thermogravimetry and differential scanning calorimetry, x-ray powder diffraction, scanning electron microscopy, and vibrating sample magnetometer. A high-crystallized LaCaMnNiO with an orthorhombic structure is obtained when the precursor is calcined at 900C in air for 3 h. Crystallite size of LaCaMnNiO increases with the increase of Ni content, attributed to the decrease of lattice strains of the LaCaMnNiO with the increase in Ni content. Nickel substitution can markedly improve coercivity and specific magnetization of LaCaMnNiO. The coercive field (9 Oe) of LaCaMnNiO is higher, even at 293 K, indicating that LaCaMnNiO continues being ferromagnetic above 260 K (Curie temperature for LCMO). [ABSTRACT FROM AUTHOR]

Hybrid magnetic heterostructures made of epitaxial manganite LaSr MnO thin film and an intermetallic superlattice (TeCo/FeCo) were prepared on orthorhombic NdGaO substrates and characterized by means of magneto-optical Kerr effect, magnetoresistance and ferromagnetic resonance. Experimental data show that magnetic interaction between LaSrMnO and (TeCo/FeCo) is of an antiferromagnetic nature. The features observed in magnetotransport characteristics are caused by the magnetization reversal at the interface between manganite thin film and intermetallic superlattice. [ABSTRACT FROM AUTHOR]

In this study, we have investigated magnetic behavior, magnetocaloric effect and critical exponent analysis of La 0.7-x Eu x Sr 0.3 MnO 3 (x = 0.0, 0.1, 0.2, 0.3) manganites synthesized through solid state reaction route. The crystallographic data obtained from refinement of X-ray diffraction patterns reveal that crystal structure changes from rhombohedral (for x = 0.0) to orthorhombic (for x ≥ 0.1). The average ionic radius of A-site is decreased from 1.384 Å (for x = 0.0) to 1.360 Å (for x = 0.3) with Eu 3+ substitution which in turn decreases the Mn-O-Mn bond angles. Magnetization measurements are performed in the vicinity of T C to determine magnetocaloric effect (MCE) and critical field behavior. The maximum magnetic entropy change ( Δ S M max ) (for μ 0 ΔH = 6 T ) increases with the Eu 3+ substitution from 3.88 J/kg K (for x = 0.0) to 5.03 J/kg K (for x = 0.3) at the transition temperature. The critical field behaviour of compounds was analysed using various methods such as modified Arrott plots, Kouvel-Fisher method and critical isotherm to determine critical temperature and critical exponents ( β , γ and δ ). The obtained critical exponents are in good accordance with scaling relation. The temperature dependence of the order parameter n , for different magnetic fields, is studied using the relation ΔS M αH n . The values of n are found to obey the Curie-Weiss law for temperatures above the transition temperature. The rescaled change in entropy data for all compounds collapses into the same universal curve, revealing a second order phase transition. [ABSTRACT FROM AUTHOR]

A series of polycrystalline La0.5Ca0.5Mn1−xNixO3(x = 0.00, 0.025, 0.050, 0.075, 0.100 and 0.125) was synthesised using solid state reaction. Measurements in a cooling and warming cycle between 300 and 80 K were carried out to study the Ni-doping effects on the electrical resistivity, thermopower and magnetisation of single-phase La0.5Ca0.5Mn1−xNixO3. Partial substitution of Ni for Mn leads to the suppression of charge ordering state, the evidence of which is shown by the dramatic decrease in electrical resistivity and thermal hysteresis width in electrical resistivity, thermopower and magnetisation. However, the magnitude of both electrical resistivity and thermopower increases with increasing Ni content. This can be attributed to an increase in the Mn4+concentration, which favours the antiferromagnetic state and leads to a gradual disappearance of ferromagnetic double exchange interaction. Besides, the metal–nonmetal transition temperature decreases with increasing Ni content untilx = 0.075, which might arise from increased electron–phonon coupling due to less ordered spins at temperatures above ferromagnetic transition. For samples withxgreater than 0.075, no metal–nonmetal transition is observed due to the suppression of double exchange mechanism. [ABSTRACT FROM PUBLISHER]

The orthorhombic Pr 0.8 Na 0.2−x K x MnO 3 (x = 0.10 and 0.15) manganites are prepared by using the solid state reaction at high temperatures. The critical exponents (β, γ, δ) are investigated through various techniques such as modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis based on the data of the magnetic measurements recorded around the Curie temperature. The critical exponents are derived from the magnetization data using the Kouvel-Fisher method, are found to be β = 0.32(4) and γ = 1.29(2) at T C ~ 123 K for x = 0.10 and β = 0.31(1) and γ = 1.25(2) at T C ~ 133 K for x = 0.15. The critical exponent values obtained for both samples are comparable to the values predicted by the 3D-Ising model, and have also been verified by the scaling equation of state. Such results demonstrate the existence of ferromagnetic short-range order in our materials. The magnetic entropy changes of polycrystalline samples with a second-order phase transition are investigated. A large magnetic entropy change deduced from isothermal magnetization curves, is observed in our samples with a peak centered on their respective Curie temperatures (T C ). The field dependence of the magnetic entropy changes are analyzed, which show power law dependence Δ S max ≈ a ( µ 0 H ) n at transition temperature. The values of n obey to the Curie Weiss law above the transition temperature. It is shown that for the investigated materials, the magnetic entropy change follow a master curve behaviour. The rescaled magnetic entropy change curves for different applied fields collapse onto a single curve for both samples. [ABSTRACT FROM AUTHOR]

Based on the modified Arrott plots and the critical isotherm analysis, the critical exponents of both LaCaMnO and LaCaAgMnO systems have been comprehensively studied and investigated near the paramagnetic-ferromagnetic (PM-FM) phase transition. Critical exponents, β, γ, and δ, which are corresponding to the thermal variation of the spontaneous magnetization, initial susceptibility, and the isothermal magnetization, respectively, obeyed the Widom scaling law δ = 1 + γ/β. It indicates thus the validity the obtained results. We performed then another analysis of the critical behavior via the magnetocaloric effect presenting an accord with the analysis of magnetization measurements. Relative cooling power (RCP) follows the evolution of the magnetic field as RCP ∼ H . The acquired critical exponents were in conformity with those gotten from the modified Arrott plots and Widom scaling law. [ABSTRACT FROM AUTHOR]

We have investigated the effects of barium deficiency on structural, magnetic and magnetocaloric properties of La0.6Nd0.1Ba0.3−xMn0.9Cr0.1O3(x= 0, 0.05 and 0.1) manganites prepared using the solid-state reaction. All the studied samples crystallize in the orthorhombic structure phase withPnmaspace group. Magnetization versus temperature showed that the samples exhibit a second-order paramagnetic to ferromagnetic transition with a decrease of the Curie temperature (TC) from 275 K forx= 0–235 K forx= 0.1. The increase of barium deficiency leads to the decrease of the maximum magnetic entropy changeand relative cooling power values from (4.40 J.kg−1K−1and 262.94 J.kg−1, forx= 0) to (2.78 J.kg−1K−1and 159.41 J.kg−1, forx= 0.1) for an applied magnetic fieldμ0H= 5 T. These values are compared favorably with those of some other reported manganites, making our samples promising candidates for the magnetic refrigeration technology. [ABSTRACT FROM AUTHOR]

Non-volatile resistance change under electric stimulation in many metal-oxides is a promising path to next generation memory devices. However, the underlying mechanisms are still not fully understood. In situ transmission electron microscopy experiments provide a powerful tool to elucidate these mechanisms. In this contribution, we demonstrate a TEM lamella geometry for in situ biasing with two fixed electrode contacts ensuring low and stable contact resistances. We use Pr 1-x Ca x MnO 3-δ sandwiched by Pt electrodes as model system. The evolution of manganese valence state during electric stimulation in different environments is mapped by means of electron energy loss spectroscopy with high spatial resolution in STEM. Correlation of Mn valence with local oxygen content is found. In addition to electrically driven switching, beam-induced redox reactions in oxygen environment are observed. This effect might be restricted to thin lamellae. In general, our results support that bulk oxygen electromigration is the relevant mechanism for non-volatile resistive switching in PCMO. [ABSTRACT FROM AUTHOR]

We investigated the influence of silicone (Si) doping on the structural, magnetic and electrical properties of polycrystalline sample La 0.6 Gd 0.1 Sr 0.3 Mn 0.8 Si 0.2 O 3 (LGSMSiO), prepared by sol–gel method. The crystallographic study showed that the sample crystallizes in orthorhombic system with Pnma space group. The relationship between the electrical and magnetic properties of manganites was traced through analyzing the dependence of LGSMSiO resistivity on temperature. The measurement of resistivity versus the temperature ρ(T) showed a transition change from ferromagnetic (FM) to paramagnetic (PM) at Curie temperature (T C ), this usually accompanied by a simultaneous metal-semiconductor (M-semiconductor) transition. Resistivity decreased with increasing the applied magnetic field. The values of T M-semiconductor were found to move towards a high temperature side with increasing the magnetic field. The critical properties of electron doped manganite LGSMSiO were investigated on the data of static magnetization measurements around the second order ferromagnetic-paramagnetic transition region T C . The magnetic data analyzed in the critical region using Kouvel-Fisher method yield the critical exponents of γ = 1.013 ± 0.02 with T C = 270.69 ± 0.22 K (from the temperature dependence of inverse initial susceptibility above T C ) and β = 0.2535 ± 0.0032 with T C = 269.89 ± 0.12 K (from the temperature dependence of spontaneous magnetization below T C ). The critical magnetization isotherm M(T C , μ 0 H) gives δ = 5.01 ± 0.03. The critical exponents found in this study obeyed the Widom scaling relation: δ = 1+γ/β, implying that the obtained values of γ and β are reliable. The exponents values obtained from resistivity were quite close to those predicted by the tricritical mean-field model. These results were in good agreement with the analysis of the critical exponents from magnetization measurements. The electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of the ferromagnetic metallic regions and the paramagnetic semiconductor regions. So, we found that the estimated results were in accordance with the experimental data. The magnetocaloric value is 5.35 J/kgK, extracted from the M(μ 0 H) curves. [ABSTRACT FROM AUTHOR]

The effects of the substitution of La 3+ by smaller rare-earth ion Pr 3+ on the structural, magnetic and magnetocaloric properties of (La 1- x Pr x ) 0.67 Pb 0.33 MnO 3 (0.0 ≤ x ≤ 0.3) compounds prepared by sol-gel method have been investigated. X-ray diffraction (XRD) showed that samples crystallize in the orthorhombic perovskite structure with Pnma space group. Thermomagnetic measurements indicate that all the samples exhibit a magnetic transition from ferromagnetic to paramagnetic phase with increasing temperature. Curie temperature, T C , systematically decreases from 358 K for x = 0.0 to 330 K for x = 0.3 as the average ionic radius of the A-site elements. The magnetic entropy change, Δ S M , was calculated from the isothermal magnetization measurements as a function of applied magnetic field at several temperatures around T C . The maximum of magnetic entropy change was found to be 4.43, 3.08, 3.33 and 2.97 Jkg −1 K −1 for x = 0.0, 0.1, 0.2 and 0.3, respectively, for a magnetic field change of 4.8 T. The field dependence of the magnetic entropy change is also analyzed and can be expressed by a power law Δ S m m a x = a ( μ 0 H ) n , where the magnetic-ordering parameter is n = 0.59, 0.62, 0.62 and 0.65 at 4.8T applied magnetic field for x = 0.0, 0.1, 0.2 and 0.3 samples, respectively. Arrott plots and universal behavior of the scaled entropy change curves show that all samples display a second order magnetic phase transition. [ABSTRACT FROM AUTHOR]

We report the magnetic properties and critical behavior of La 0.7 Sr 0.3 Mn 1- x Cu x O 3 ( x = 0.02 and 0.04) perovskite manganites. Results of temperature-dependent magnetization show that the Curie temperature decreases from 360 K ( x = 0.02) to 356 K ( x = 0.03) with increasing Cu content. Field dependence of isothermal entropy change data is used to estimate the critical exponents, and the results satisfied the requirements of the scaling law. Calculated critical exponents are β = 0.4641, γ = 1.1623, and δ = 3.546 for x = 0.02, and β = 0.4486, γ = 1.2024, and δ = 3.6805 for x = 0.04. These results indicate that La 0.7 Sr 0.3 Mn 1- x Cu x O 3 can be characterized by long-range mean-field behavior. Thus, the field dependence of magnetic entropy change can be effectively used in studying the critical behavior of magnetic materials. [ABSTRACT FROM AUTHOR]

Artificially constructed oxide heterointerfaces have attracted much attention. Herein, the novel all-perovskite p-n heterojunction composed of a colossal magnetoresistive manganite La0.7Sr0.3 MnO3 (LSMO) and an n-type transparent semiconducting BaSnO3 (BSO) is designed via optimizing the growth condition. This LSMO/BSO p-n junction exhibits good rectification with a forward-to-reverse ratio of 275 at 1 V, high photo detection capability with a photo-to-dark current of 581.9 at -0.5 V, high ultraviolet light sensitivity with a UV (360 nm)-to-visible (532 nm) ratio of ∼2.4 × 103, and a significantly magneto-tunable photocurrent with a variation ratio of ∼1.25 % under 532 nm illumination and 0.5 T magnetic field. As a result, combining synergistically the functionality of diode and magnetically tunable photo detector, the LSMO/BSO p-n junction is a promising candidate for advanced magneto-optoelectronic devices. [ABSTRACT FROM AUTHOR]

Influence of alkaline earth element doping in the A-site on the structure, magnetic and magnetocaloric properties of La 0.7 Ca 0.3-x A x MnO 3 (A = Sr and Ba; x = 0, 0.15 and 0.3) perovskite manganites have been investigated. X-ray diffraction data indicates that samples x = 0 and 0.15 crystallize in the orthorhombic structure (space group Pnma ), whereas samples x = 0.3 belong to the rhombohedral structure (space group R -3 c ). Substitution of Sr or Ba for Ca plays an important role in the increase of Curie temperature ( T C ) and modification the nature of the magnetic phase transition in materials. Sample x = 0 exhibits the first-order phase transition (FOPT) with a large magnetic entropy change (Δ S m ), whereas samples x = 0.15 and 0.3 exhibit the second-order phase transition (SOPT) characterizations and the moderate values of Δ S m . Using the modified Arrott plots method, the critical behaviors around T C for SOPT samples have been investigated through the values of critical parameters ( T C , β , γ , and δ ). We pointed out that Ba-doping favors establishing long-range ferromagnetic order, contrary to the case of Sr-doping. [ABSTRACT FROM AUTHOR]

This paper deals with tunneling magnetoresistance in a composite system of the so-called 0–3 connectivity, in which ferromagnetic (FM) metallic nanoparticles La1–xSrxMnO3 (0-D objects) are embedded in the (3-D) insulating matrix of TiO2. The sample fabrication included the sol–gel preparation of manganite particles of the x = 0.35 composition and 25 nm mean crystallite size, their coating by TiO2, and compacting the products by spark plasma sintering (SPS). A comparative nanogranular sample was prepared by SPS of bare manganite particles. The resistivities of the composite and comparative samples are 100 000 and 100 times higher compared to those of bulk metallic La1–xSrxMnO3. Otherwise, the temperature dependence observed in the nanogranular La1–xSrxMnO3 sample is similar to single crystal data, and marked localization is absent also in the La1–xSrxMnO3@TiO2 nanocomposite. The data taken in applied fields up to 4 T reveal effects typical for grain-boundary tunneling in manganites, namely, the coexistence of the low-field magnetoconductance (LFMC), reflecting the field-induced alignment of FM cores, and high-field linear magnetoconductance (HFMC) that is generally ascribed to the effect of spin canting at localized Mn4+ sites in the interface. This is considered as a signature for resonant tunneling of spin-polarized carriers, theoretically treated by Lee et al [1]. The present results show that the total extent of LFMC makes 45% in the La1–xSrxMnO3@TiO2 nanocomposite and 21% in the La1–xSrxMnO3 nanogranular sample. The slope of HFMC has been determined to 5.4% and 4.9% per Tesla, respectively. The large LFMC effect observed in the nanocomposite exceeds the theoretical prediction of 33% for the second-order tunneling, which might suggest for higher order tunneling via resonant states. [ABSTRACT FROM AUTHOR]

The results of Co substitution for Mn in nanostructured La1-xSrxMn1-yCoyO3 films ( $x = 0.2$ ) grown on polycrystalline Al2O3 substrates by pulsed-injection metal-organic chemical vapor deposition technique, are presented. The Co content y in the films was changed as follows: 0; 0.023; 0.053; 0.078. The resistivity ( $\rho )$ dependences on temperature in zero magnetic field was investigated in the temperature range 5–300 K. It was found that the increase in Co content up to 0.078 results in the decrease of metal-insulator transition temperature and increase of the resistivity. The results of nanostructured films are compared with the epitaxial films grown on LaAlO3 substrate keeping the same technological conditions. The magnetoresistance (MR) and MR anisotropy (MRA) were investigated at room temperature (290 K) in permanent magnetic fields up to 2.35 T, and pulsed magnetic fields up to 20 T. It was found that the highest MR values are obtained for the intermediate Co content: $y = 0.053$ , while the MRA decreased with the increase of Co content. The results are discussed within the double-exchange interaction model for the perovskite oxides. The possibility to apply the manganite-cobaltite films for the development of room temperature B-scalar magnetic field sensors is considered. [ABSTRACT FROM AUTHOR]

LaDyCaMnVO, prepared by solid-state route, was characterized using x-ray diffraction at room temperature. The Rietveld refinement shows that the sample crystallizes in orthorhombic structure with Pbnm space group. A secondary phase LaVO has been also detected. The temperature dependence of the magnetization was investigated to determine the characteristics of the magnetic transition. The sample exhibits a paramagnetic-ferromagnetic transition (PM-FM) at T = 81 ± 0.7 K when temperature decreases. The study of the inverse of susceptibility reveals the presence of ferromagnetic clusters in the paramagnetic region. A metamagnetic transition was observed from the M( H) curves and the magnetic entropy change was calculated from magnetization curves at different temperatures in order to evaluate the magnetocaloric effect. [ABSTRACT FROM AUTHOR]

In the present paper we have studied the effect of Sm doping on the magnetic and magnetocaloric properties of La 0.7-x Sm x Ba 0.3 MnO 3 (0 ≤ x ≤ 0.2) compounds. These sample have been synthesized by conventional solid state reaction method. The analysis of synthesized samples by X-ray diffraction showed that the formation of single phase compositions and doping of La 3+ by Sm 3+ ion converted the chemical structure form rhombohedral ( R-3C ) to orthorhombic ( Imma ). The magnetic study measurement specified that the ferromagnetic double exchange interaction is weakened with increasing Sm content as a consequence of the curie temperature (T c ) shift in lower temperature from 340 K for x = 0, 290 K for x = 0.1 and 225 K for x = 0.2 compounds. Using the Banerjee’s criterion plots, it is found that the phase transition for all samples in the second-order. All reported compounds exhibit a maximum and large magneto-caloric effect near the Curie temperature (T c ). The magnitude of the maximum magnetic entropy change is found to be decrease with increasing of Sm doping content i.e. 4.39 J/kg K for x = 0, 4.22 J/kg K for x = 0.1 and 2.48 J/kg K for x = 0.2 in applied field change of 5T. The trend of large entropy change and the convenient adjustment of the Curie temperature make these oxides useful for magnetic refrigeration in an extended high and low temperature even at near room temperature. [ABSTRACT FROM AUTHOR]

The critical behavior associated with the magnetic phase transition has been investigated by in La 0.8 Na 0.2− x □ x MnO 3 (0.00 ≤ x ≤ 0.15) (□ is the sodium deficiency). The critical exponents are estimated by various techniques such as the modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. Compared to standard models, the critical exponent values determined in our work are close to those expected by the tricritical model (β = 0.25, γ = 1, and δ = 5) for x = 0.00 and 0.05 samples and by mean field theory (β = 0.5, γ = 1, and δ = 3) for x = 0.10 and 0.15 samples. We conclude that the Na deficiency rate affect the critical exponents. [ABSTRACT FROM AUTHOR]

Dy 0.5 (Sr 1-x Ca x ) 0.5 MnO 3 (x = 0 and x = 0.3) manganites were synthesized using sol-gel method. Both samples exhibited an insulating behavior in the whole temperature range. Even the application of 5 T magnetic fields does not change this state. Conduction mechanisms were also investigated. The I–V characteristics of both samples present Ohmic behavior at minor voltages. Magnetoresistance and electroresistance were also studied. The thermal variation of Hall resistivity of Dy 0.5 Sr 0.5 MnO 3 was determined in cooling down and warming up processes revealing electron-like type of charge carriers. Temperature coefficient of resistance shows significant values for both systems making them good candidates for bolometer applications. [ABSTRACT FROM AUTHOR]

We present a systematic study on structural, electrical and magnetic properties of low bandwidth compounds of the family Sm 1−x Sr x MnO 3 . The samples were prepared by conventional solid-state reaction. Rietveld analysis of XRD results show that the samples crystallized in orthorhombic crystal structure with Pbnm space group. The unit volume is decreasing with increasing Sr concentration. The electrical resistivity is suppressed with application of magnetic field. Huge magnetoresistance has been observed for samples with x =0.4 and x =0.5. The validity of the percolation model has been verified in the entire temperature range. The magnetic studies show that the field-induced critical temperature and Neel temperature transitions are seen in all compounds. The samples with x =0.2 and 0.3 show positive S values in the entire temperature range. The Seebeck coefficient (S) of the x =0.5 sample is negative in the entire temperature range, and for the sample with x =0.4 exhibits a crossover in S value from positive to negative values. The analysis of S data indicates that the small polaron hopping model is valid in the high temperature region. [ABSTRACT FROM AUTHOR]

In the present communication the results on thermal conductivity, Seebeck coefficient and specific heat of Pr 2/3 Sr 1/3 MnO 3 :PdO composites are reported. All the samples exhibit a pronounced anomaly in thermal conductivity ( κ ) at their respective Curie temperatures, T C of the samples. It is also observed that the overall magnitude of κ decreases with increasing Pd content. The observed reduction of the total k ( T ) is discussed with various thermal scattering mechanisms. The temperature-dependent Seebeck coefficient data S ( T ) in the high temperature region is analyzed within the framework of Mott's polaron hopping model. The analysis of low-temperature S ( T ) data reveals that the electron-magnon scattering contribution dominates the thermoelectric transport at low temperatures. The magnetic contribution for the C P and change in entropy (Δ S ) during the magnetic phase transition is also evaluated. [ABSTRACT FROM AUTHOR]

Pr 0.8 Na 0.05 K 0.15 MnO 3 sample was prepared by solid-state reaction method. Refinement of the X-ray diffraction patterns shows that the sample is single phase and crystallizes in the orthorhombic structure with Pbnm space group. This result was confirmed by using the electron diffraction pattern for the sample using the [0 0 1] orientation. Analyzing temperature and field dependences of magnetization around the ferromagnetic-paramagnetic transition reveals the sample undergoing the second-order magnetic phase transition. The isothermal entropy changes Δ S as a function of temperature in different magnetic fields were determined. A phenomenological model is used to calculate magnetic and magnetocaloric properties of Pr 0.8 Na 0.05 K 0.15 MnO 3 compound. The maximum values of Δ S max and the relative cooling power (RCP) increase with increasing applied magnetic field. Landau theory and phenomenological universal curves of entropy change confirm the second order phase transition. [ABSTRACT FROM AUTHOR]

The results of investigation of colossal magnetoresistance relaxation in nanostructured La-Sr(Ca)-Mn-O films upon removal of magnetic field pulse are presented. Thin films having thicknesses of 75–350 nm grown by pulsed injection metal–organic chemical vapor deposition technique were studied in pulsed magnetic fields having duration of 0.9 ms and amplitudes of 2–12 T. It was obtained that “fast” relaxation process occurring in hundred microseconds time scale exhibits anisotropy: the magnitude of remnant resistivity is approximately three times smaller and the process is faster when magnetic field is applied perpendicular to the film plane in comparison with in-plane direction. The dynamics of this relaxation process was analyzed using Kolmogorov–Avrami–Fatuzzo model, taking into account nucleation and reorientation of magnetic domains into equilibrium state. The “fast” remnant relaxation was not observed after the application of longer pulses (20 ms) having amplitude of 60 T. Influence of remnant relaxation on operation of B-scalar magnetic field sensors based on nanostructured manganite films is discussed. [ABSTRACT FROM PUBLISHER]

The results of structure and magnetoresistance (MR) of nanostructured La1–xCaxMnyO3 (LCMO) films, grown at different gas pressure (from 3 to 7 Torr) by pulse injection metal–organic chemical vapor deposition (MOCVD) technique, are presented. The MR was investigated in pulsed magnetic fields up to 60 T in the temperature range 1.5–294 K. The results were analyzed from the perspective of using these films for magnetic field sensors operating at low temperatures. It was demonstrated that with the increase of Ar + O2 gas pressure, the surface morphology of the films becomes rougher and grain size increases. Also, the ratio of Mn/(La + Ca) increases with the increase of the pressure. Large MR of the films was observed in a wide temperature range below the ferromagnetic–paramagnetic phase transition. It was shown that at cryogenic temperatures, the films grown at gas pressure of 3 Torr have higher sensitivity in lower magnetic field range (<10 T), while in high magnetic fields (20–60 T), the properties of films grown at higher gas pressure 5–7 Torr are favored. The obtained results allow evaluating the influence of MOCVD growth pressure on MR and sensitivity to the magnetic field of LCMO manganites used for pulsed magnetic field sensors. [ABSTRACT FROM PUBLISHER]

We have investigated resistivity rise and relaxation of thin epitaxial (EP) and nanostructured polycrystalline (NP) La-Sr-MnO films after thermal shock. Samples of 400-nm thickness La0.83Sr0.17MnO3 were grown on LaAlO3 substrate for EP films, and on “lucalox” for NP films. The thermal shocks were induced by 1064-nm 30-ps Nd:YAG laser pulses with pulse energy at the sample between 1.5 and 2 mJ. Samples were treated by single laser pulse at different ambient temperatures when the film was in ferromagnetic or paramagnetic state. In the films at temperatures ( T0) lower than phase transition temperature ( Tm) immediately after the laser pulse, the resistance of the sample has increased. It was found that the rise time of resistance response increases with increase of T0 in the range from few hundred ps to several ns. Meanwhile, the time of total relaxation of resistance back to initial level was in the range from 10 to 35 \mu \texts . For both types of films, the experimental results of cooling process showed longer relaxation time than that of obtained in theoretical modeling. Possible reasons were discussed taking into account magnetic ordering processes. The obtained results help to evaluate the influence of fast temperature changes during high pulsed magnetic field measurements with B-scalar sensors based on La-Sr-MnO films. [ABSTRACT FROM PUBLISHER]

Polycrystalline Pr 0.75 Na 0.25- x K x MnO 3 ( x = 0, 0.05, 0.10, 0.15 and 0.20) ceramics were prepared using conventional solid-state method and their structural, magnetic and electrical transport properties were investigated. Magnetization versus temperature measurements showed un-substituted sample exhibited paramagnetic behavior with charge-ordered temperature, T CO around 218 K followed by antiferromagnetic behavior at transition temperature, T N ∼ 170 K. K + -substitution initially weakened CO state for x = 0.05–0.10 then successfully suppressed the CO state for x = 0.15–0.20 and inducing ferromagnetic-paramagnetic transition with Curie temperature, T C increased with x . In addition, deviation of the temperature dependence of inverse magnetic susceptibility curves from the Curie-Weiss law suggests the existence of Griffiths phase-like increased with x . Magnetization versus magnetic field curves show existence of hysteresis loops at T < 260 K ( x = 0) and T < 180 K ( x = 0.05–0.10), which related to metamagnetic transition occurring at critical field. Electrical resistivity measurements showed an insulating behavior for x = 0 sample while for x = 0.05–0.20 samples showed metal-insulator transition and transition temperature, T MI increased with x . The increased in T C and T MI are attributed to the increase in tolerance factor which indicates reduction in MnO 6 octahedral distortion consequently enhanced double exchange interaction. [ABSTRACT FROM AUTHOR]

The influence of strontium substitution on lanthanum site in La 1-x Sr x MnO 3 manganites has been investigated with x ranging from 0.55 to 0.62 in the 130–400 K temperature range. Powder X-ray diffraction reveals structural changes from rhomboedral to tetragonal and to orthorhombic structures upon increasing Sr substitution. Magnetic properties also show a rich variety of phases and behaviors, including coexistence of phases above Curie temperature. The electron spin resonance measurements allow quantifying paramagnetic phases and properties with randomly distributed spins and ferromagnetic phases or inclusions with oriented spins giving rise to a local magnetic field. When x = 0.55, 0.57, the ferromagnetic state is the minor phase embedded in a paramagnetic matrix. Conversely, when x increases, the ferromagnetic phase grows and becomes the only phase observed for x = 0.62. [ABSTRACT FROM AUTHOR]

Presently, the effect of divalent Ca ions on the structural and transport properties of YMnO3is studied. A series of (Y1-xCaxMnO3x = 0.00, 0.03, 0.05, 0.1, 0.25) samples were synthesized by solid state reaction method. X-ray diffraction shows that pure YMnO3have hexagonal while Ca doped compounds possess mixed (hexagonal and orthorhombic) phase for all concentrations of Ca. Ferroelectric behavior of all samples was also investigated by PE loop. Furthermore, dielectric constant is found to improve after Ca doping which is understood in terms of electronic phase separation that generally occurs in charge ordered manganites. [ABSTRACT FROM AUTHOR]

In this work, we are interested in the study of the critical behavior and the Landau theory of Pr 0.63 A 0.07 Sr 0.3 MnO 3 (A=Pr, Sm and Bi) compounds. The critical exponents of all our samples were studied using the magnetic field dependent isothermal magnetization around Curie temperature T C , based on various techniques. The validity of our critical exponents is confirmed by the scaling analysis. The study revealed that tricritical mean field model is the best for calculating the critical exponents for all our samples. The substitution of praseodymium by samarium and bismuth does not change the universality class. Using Landau theory, we have confirmed that the magnetic transition around T C is of second-order. An agreement was found between the (-ΔS) values estimated by Landau theory and those obtained using Maxwell relation for a magnetic field equal to 2 T, which shows the validity of this theory for all our compounds. The deviation obtained for bismuth and samarium based samples below T C can be attributed to the existence of some antiferromagnetic domains in the ferromagnetic phase. [ABSTRACT FROM AUTHOR]

Ac susceptibility and thermoelectric power properties of bulk La 0.90 Li 0.10-x Na x MnO 3 (0 ≤ x ≤ 0.10 at. %, step 0.02 at. %) compounds have been studied. The temperature dependence of the ac susceptibility measurements showed a cusp and shoulder below Curie temperature (T C ) related to a frequency-independent and dependent peak in χ ″ (T) curves respectively. Slower spin dynamics and the cluster sizes augment with increases the Na content. In terms of magneto-transport a properties, a peak is observed in vicinity of T ms transition, which it has industrial applications. The thermoelectric power data analyzed at low temperature by the magnon and phonon drag concept, while at high temperature by small polaron conduction mechanism. We found an unexpected correlation of structures in MR (T) and S(T) curves. [ABSTRACT FROM AUTHOR]

La 0.6 Ca 0.2 Ba 0.2 MnO 3 ceramics are prepared by an original route, combining soft chemistry and Spark Plasma Sintering, within a few minutes at 700 °C and by the solid-state reaction at high temperatures with an annealing temperature of 1200 °C. We have studied the leverage of the powder synthesis method on the structural, morphological, magnetic and magnetocaloric properties of the samples. X-ray diffraction analysis using Rietveld refinement revealed that our materials crystallize in the rhombohedral system with R 3 ¯ c space group for the sample prepared by the Polyol-Spark Plasma Sintering method and in the orthorhombic structure with Pbnm space group for the sample synthesized by the solid-state reaction. Magnetization measurements versus temperature under magnetic applied field of 0.05 T show a paramagnetic-ferromagnetic phase transition for both samples. The Arrott plots reveal that ours materials undergo a second-order phase transition. The maximum values of the magnetic entropy change ( − Δ S M max ) under the magnetic field change of 5 T are 2.4 and 4.7 J/kg K for La 0.6 Ca 0.2 Ba 0.2 MnO 3 synthesized by using solid-state reaction and Polyol-Spark Plasma Sintering methods respectively. The highest value of the relative cooling power RCP is found to be 244 J/kg for the Polyol-Spark Plasma Sintering sample under 5 T. These results are interesting enough and suggest that the Polyol-Spark Plasma Sintering synthesis method is a feasible route to prepare high quality perovskite material for magnetic cooling application. [ABSTRACT FROM AUTHOR]

The magnetoresistance (MR) effect is widely used in technologies that pervade the world, from magnetic reading heads to sensors. Diverse contributions to MR, such as anisotropic, giant, tunnel, colossal, and spin-Hall, are revealed in materials depending on the specific system and measuring configuration. Half-metallic manganites hold promise for spintronic applications but the complexity of competing interactions has not permitted the understanding and control of their magnetotransport properties to enable the realization of their technological potential. This study reports on the ability to induce a dominant switchable magnetoresistance in La0.7Sr0.3MnO3 epitaxial films at room temperature (RT). By engineering an extrinsic magnetic anisotropy, a large enhancement of anisotropic magnetoresistance (AMR) is achieved which at RT leads to signal changes much larger than the other contributions such as the colossal magnetoresistance. The dominant extrinsic AMR exhibits large variation in the resistance in low field region, showing high sensitivity to applied low magnetic fields. These findings have a strong impact on the real applications of manganite-based devices for the high-resolution low field magnetic sensors or spintronics. [ABSTRACT FROM AUTHOR]

The temperature dependence of magnetic susceptibility χ (Τ), 78<Τ(Κ)<295, and electrical resistivity ρ (T), 1059.634) decreases to a minimum for sample x=0.6. Highest resistivity (ρ) and ac susceptibility (χ) are observed for x=0.6. Metal- semiconductor transition temperature T ρ decreases gradually with Mg doping, in contrast to ferromagnetic-paramagnetic Curie temperature Tc which shows weak dependence on Mg doping level. Low temperature resistivity showed upturn in the temperature range 28–37 K. At high temperatures, variable range hopping conduction predominates with density of states N(E f ) ~3×10 19 −6×10 19 (eV −1 cm −3 ). Low temperature resistivity follows ferrometallic nano-particle relation: ρ=ρ o +ρ 1 T 2 +ρ 2 T 4.5 . AC susceptibility of x=0.0 and 0.6 fit well to Curie law, samples x=0.2, 0.4, 0.8 and 1.0 are better described in the framework of Neel ferrimagnetism. Transport and magnetic susceptibility results are interpreted in terms of core-shell model where ferromagnetic core interacts anti-ferro-magnetically with ferromagnetic shell. [ABSTRACT FROM AUTHOR]

We have studied the effect of replacing Mn 3+ by Cr 3+ on the structure, transport and magnetism in the bilayered manganite LaSr 2 Mn 2 O 7 . Although no structural transition was observed in LaSr 2 Mn 2−y Cr y O 7 (0.1 ≤ y ≤ 0.6), the electrical transport and the magnetic properties were found to be affected significantly by this substitution. Substitution of Cr 3+ reduces the conductivity by restricting the hopping of small polarons. Magnetization increases with increasing Cr 3+ concentration suggesting that Cr 3+ -ions induce ferromagnetic moments . The ferromagnetic and an antiferromagnetic phase observed above ∼60 K merge into an inhomogeneous phase below this temperature. Thermopower yields an essentially concentration independent charge density nearly equal to its value for chromium free composition inspite of its expected decrease with this substitution suggesting that the small charge density of the insulating AFM phase is supplemented by the free carriers in the FM phase. The inhomogeneous phase shows a relaxor type behavior which contrasts with the spin glass behavior seen in La 0.46 Sr 0.54 Mn 0.98 Cr 0.02 O 3 having an identical AFM magnetic state. The difference is attributed to the non-JT character of Cr-ions which reduce the distortion of the Mn O octahedra located within the FM domains. With a higher lattice strain in the surrounding AFM matrix the carriers remain confined within the FM domains leading to the relaxor type behavior. [ABSTRACT FROM AUTHOR]