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The structural, magnetic, and magnetocaloric properties of La0.7Sr0.3-xLixMnO3 (0 ≤ x ≤ 0.15) samples have been investigated. All our samples were synthesized using the sol–gel technique at low temperature. The Rietveld refinement of the X-ray powder diffraction shows that the La0.7Sr0.3-xLixMnO3 compounds crystallize in a rhombohedral system with R 3 ¯ c space group. Magnetization measurements versus temperature showed that all our investigated samples display a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature, TC, decreases with increasing Li content from 365 K for x = 0 to 194.4 K for x = 0.15. The maximum of the magnetic entropy change, Δ S M Max , under an applied magnetic field change of 2 T is found to be 1.97, 1.05, 1.07, and 1 J kg−1 K−1 for x = 0, 0.05, 0.1, and 0.15 respectively. The relative cooling power reaches 82.1, 80.6, 83.2, and 102.5 Jkg−1 for x = 0, 0.05, 0.1, and 0.15, respectively, under the same magnetic field change of 2 T. [ABSTRACT FROM AUTHOR]

Hard hexagonal barium ferrite BaFe12O19 (BaM), as well as core–shell structure BaFe12O19-TiO2 composite nanoparticles, was successfully prepared by solid state reaction. An interesting photocatalytic activity has been noticed for the first time in pure BaM and doped TiO2 nanopowders. The obtained powders can photodegrade organic pollutants in the dispersion system effectively and can be recycled easily using a magnetic field. The BaFe12O19-TiO2 magnetic photocatalyst is composed of two parts: (1) TiO2 shell used for photocatalysis and (2) BaFe12O19 core for separation by the magnetic field. The photocatalytic activity of the as-prepared magnetic photocatalyst is enhanced with BaFe12O19 doping. Besides, the saturation magnetizations of BaFe12O19-TiO2 nanoparticles decreased in comparison to pure hexaferrite, while the coercivity remains almost constant. [ABSTRACT FROM AUTHOR]

The high-energy ball milling method has been used to synthesize the polycrystalline powders La0.5Ca0.5Mn1−xVxO3 (x = 0.05, x = 0.10). The Rietveld refinement technique shows that the samples crystallized in the orthorhombic structure with the Pbnm space group. The La0.5Ca0.5Mn0.95V0.05O3 exhibits a second-order phase transition from paramagnetic (PM) to ferromagnetic (FM) state at TC = 208 ± 1 K followed by a second one from FM to charge ordering–antiferromagnetic state at TN = 150.0 ± 0.1 K when decreasing temperature. The substituted sample with 10% amount of vanadium dopant corresponds to the disappearance of the charge-order phase; meanwhile, it was suppressed for 5% of the vanadium in the solid-state route. The Curie temperature TC increases with vanadium content from 208 ± 1 K for x = 0.05 to 255 ± 1 K for x = 0.10. The values of the maximum of the magnetic entropy change under a magnetic field change of 5 T are found to be 2.95 ± 0.04 J kg−1 K−1 and 5.42 ± 0.07 J kg−1 K−1 corresponding to a relative cooling power RCP = 128.4 ± 0.3 and 220.8 ± 0.7 for x = 0.05 and x = 0.10 respectively. The order of phase transition has been determined. The critical exponent study has been performed for La0.5Ca0.5Mn0.9V0.10O3 by using the Arrott plot, Kouvel–Fisher method, and critical isotherm analysis. The measured β, γ, and δ values are in agreement with those expected for the tricritical mean-field model. [ABSTRACT FROM AUTHOR]

Structural, magnetic, and magnetocaloric effect (MCE) properties and the critical behavior of the La0.45Pr0.2Sr0.35MnO3 sample prepared by the sol–gel method have been investigated. The X-ray diffraction characterization reveals that our sample crystallizes in the orthorhombic structure with Pnma space group. Magnetization versus temperature measurement shows that our compound exhibits a ferromagnetic–paramagnetic transition. The Curie temperature is found to be 348 K. Close to this temperature, the maximum values of the magnetic entropy change (ΔSM) and the relative cooling power (RCP) are found to be 2.84 J/kg/K and 230 J/K under µ0H = 5 T, respectively. The Arrott plots revealed that this compound exhibits a second-order magnetic phase transition at TC. The critical behavior has been investigated by several techniques which are the modified Arrott plot method, the Kouvel–Fisher method, and the critical isotherm analysis. The obtained critical exponents β, γ, and δ are consistent with those predictions of the mean-field model. Their reliability was confirmed by Widom's scaling relation, as well as the universal scaling hypothesis. [ABSTRACT FROM AUTHOR]

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 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 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 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. [ABSTRACT FROM AUTHOR]

(1− x) Cr2O3/x MoS2 (x = 0.25, 0.5, 0.75) were synthesized using the powder solid-state route. The structural, morphological, vibrational, and magnetic properties of the as-prepared MoS2/Cr2O3 samples with different Cr2O3 contents have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy, Raman spectroscopy, and vibrating sample magnetometry (VSM), respectively. The X-ray diffraction results show the presence of the parent compounds (molybdenum disulfide (MoS2) and chromium oxide (Cr2O3)) in addition to a secondary phase corresponding to chromium molybdenite Cr2Mo3O12. Raman and IR spectra were recorded, and the observed modes were analyzed and assigned to different normal modes of vibration. Magnetic characterizations revealed that all the series MoS2/Cr2O3 composites possess paramagnetic characteristics both at room temperature and at 30 K. Further, the maximum of magnetization increased with the increase of Cr2O3 content. [ABSTRACT FROM AUTHOR]

In this work, we present the study of structural, magnetic and critical behavior of LaSrCoO ( x = 0.3 and 0.5) cobaltites. X-ray diffraction analysis using the Rietveld refinement shows that the sample LaSrCoO crystallizes in a rhombohedral distorted perovskite structure with $R\overline {3} c$ space group, while LaSrCoO exhibits both phases rhombohedric and cubic, with $R\overline {3} c$ and $Pm\overline {3} m$ space groups. Our samples exhibit thermo-magnetic irreversibility behavior in the magnetization data under a magnetic applied field of 0.05 T. The temperature dependence of magnetic susceptibility at higher temperatures for LaSrCoO sample reveals the presence of the Griffiths' phase above the Curie temperature, while it follows the Curie-Weiss law perfectly for LaSrCoO. Different techniques including the modified Arrott plot, the Kouvel-Fisher method and the critical isotherm analysis have been used to analyze the paramagnetic-ferromagnetic phase transition. The values of the critical exponents associated to this transition were close to those expected in the mean-field model. The validity of the calculated critical exponents has been confirmed by the scaling equation of state. The determined critical exponents using various methods are found to follow the scaling equation with the magnetization data scaled into two different curves below and above the critical temperature. [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]

The LaDyCaMnO (LDCMO) compound prepared via high-energy ball-milling (BM) presents a ferromagnetic-to-paramagnetic transition (FM-PM) and undergoes a second-order phase transition (SOFT). Based on a phenomenological model, magnetocaloric properties of the LDCMO compound have been studied. Thanks to this model, we can predict the values of the magnetic entropy change Δ S, the full width at half-maximum δ T , the relative cooling power (RCP), and the magnetic specific heat change Δ C for our compound. The significant results under 2 T indicate that our compound could be considered as a candidate for use in magnetic refrigeration at low temperatures. In order to further understand the FM-PM transition, the associated critical behavior has been investigated by magnetization isotherms. The critical exponents estimated by the modified Arrott plot, the Kouvel-Fisher plot, and the critical isotherm technique are very close to those corresponding to the 3D-Ising standard model ( β = 0.312 ± 0.07, γ = 1.28 ± 0.02, and δ = 4.80).Those results revealed a long-range ferromagnetic interaction between spins. [ABSTRACT FROM AUTHOR]

In this work, we studied in detail the magnetic and magnetocaloric properties of the LaCaBaMnO compound according to the phenomenological model. Based on this model, the magnetocaloric parameters such as the maximum of the magnetic entropy change Δ S and the relative cooling power (RCP) have been determined from the magnetization data as a function of temperature at several magnetic fields. The theoretical predictions are found to closely agree with the experimental measurements, which make our sample a suitable candidate for refrigeration near room temperature. In addition, field dependences of ${{\Delta } S}_{\mathrm {M}}^{\max }$ and RCP can be expressed by the power laws ${\Delta S}_{\mathrm {M}}^{\max }\approx a$ ( μ H) and RCP ≈ b( μ H), where a and b are coefficients and n and m are the field exponents, respectively. Moreover, phenomenological universal curves of entropy change confirm the second-order phase transition. [ABSTRACT FROM AUTHOR]

In this paper, a profound theoretical work has been conducted on magnetic and magnetocaloric properties of La CaMnO (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 (Δ S ), the relative cooling power (RCP), and the magnetic specific heat change (Δ C ). The theoretical predictions nearly match with the experimental measurements. These materials present large magnetocaloric effect, suggesting their possible application in moderate magnetic fields. [ABSTRACT FROM AUTHOR]

Our study was to determine the critical exponents of LaCaKNaMn0 compound near the Curie temperature ( T ). The experimental results reveal that our sample undergoes a second-order magnetic phase transition. The estimated critical exponents have been determined using different techniques, such as the modified Arrott plot (MAP), the Kouvel-Fisher (KF) method, and critical isotherm (CI) analysis. The obtained values using the MAP method ( β = 0.303 ± 0.013 with T = 292.24 K, γ = 1.236 ± 0.101 with T = 293.02 K) and KF method ( β = 0.341 ± 0.007 with T = 292.48 K, γ = 1.216 ± 0.024 with T = 293.13 K) are close to 3D Ising values and their T is near room temperature. These critical exponents fulfill the Widom scaling relation δ = 1 + γ/ β. Finally, based on the critical exponents, the magnetization-field-temperature data around T collapses into two curves obeying the single-scaling relation, implying the reliability of our values. [ABSTRACT FROM AUTHOR]

In this paper, the prediction of the magnetocaloric properties has been investigated in the LaCaBa $_{\mathrm {0.15}}\square _{\mathrm {0.05}}$MnO system near the ferromagnetic-paramagnetic phase transition as a function of temperature. The data indicate that the LaCaBa $_{\mathrm {0.15}}\square _{\mathrm {0.05}}$MnO system has potential application for magnetic refrigerants in an extended high-temperature range. In addition, the magnetic entropy change distribution is quite uniform, which is desirable for an Ericsson cycle magnetic refrigerator. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of structural, magnetic, and magnetocaloric properties of LaCaNaMnO (LCNMO) prepared using both the conventional solid-state method with a consolidation stage at 1000 C and the well-known sol-gel method combined to a sintering treatment at 950 C. Rietveld refinement of the X-ray diffraction patterns indicates a rhombohedral structure with R-3C space group in both cases. It was also found that the magnetocaloric properties of LCNMO are strongly depended on the synthesis technique. In fact, a global magnetization reduction and a decrease in paramagnetic-ferromagnetic (PM-FM) transition temperature ( T) associated to an enhancement of the relative cooling power were noticed in sol-gel synthesized sample making it more suitable for magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

In this paper, the magnetic and magnetocaloric properties of LaCaMnO (LCMO), La $_{0.69}\square {~}_{0.01}$CaMnO (L) and LaCa $_{0.29}\square {~}_{0.01}$MnO (L) systems near a second-order phase transition from a ferromagnetic to a paramagnetic state, have been studied, using a phenomenological model. Based on this model, we are getting the better fits to magnetic transition and we can predict the values of the magnetocaloric effect such as magnetic entropy change, full-width at half-maximum, relative cooling power, and magnetic specific heat change from the calculation of magnetization as a function of temperature under different external magnetic fields. The maximum magnetic entropy change ${(-{\Delta } S}_{M}^{\max }) $shifts to higher values with one percent of both calcium and lanthanum deficiencies, while the relative cooling power (RCP) and the full-width at half-maximum are reduced. According to the master curve behavior for the temperature dependence of Δ S predicted for different maximum fields, this work has confirmed that the paramagnetic-ferromagnetic phase transition observed for our sample is of second order. [ABSTRACT FROM AUTHOR]

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

LaCaMnO/LaCaBaMnO (COMPI) and LaCaMnO/PrSrMnO (COMPII) composite manganites were prepared using a conventional ceramic double-sintering process. The microstructural, magnetic and magnetocaloric properties of the composites were investigated using scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). X-ray diffraction analysis using Rietveld refinement shows that the starting LaCaMnO, LaCaBaMnO and PrSrMnO manganites are single phases and crystallize in the orthorhombic system with a Pbnm space group. Magnetization measurements versus temperature for each composite reveal two magnetic transition temperatures associated to both manganites, which induces an enlargement of the magnetic entropy change peak. A better relative cooling power (RCP) value of 308 J kg around 280 K is obtained for COMPI and is about 75 % of that observed in pure Gd, which makes our composite a potential candidate for magnetic refrigeration around room temperature [ABSTRACT FROM AUTHOR]

We present in this paper the effect of calcium deficiency on the structural, magnetic and magnetocaloric in LaCa $_{0.35-\mathrm {x}}\square _{\mathrm {x}}$MnO (x =−0.15) powder samples. Our compounds were prepared using the solid-state reaction at high temperatures. Rietveld analysis show that all our synthesized samples are single phase without any detectable impurity and crystallize in the orthorhombic system with Pbnm space group. The Mn atom is coordinated by six oxygen atoms forming an irregular octahedron. The scanning electron microscopy (SEM) micrographs reveal that all the structure is characterized by various shapes and a uniform grain size which clearly increase from 1.528 μm for x = 0 to 3.36 μm for x = 0.1. Magnetic measurements as a function of temperature show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature exhibits a minimum of 228 K for x = 0.10. The maximum value of the relative cooling power RCP is obtained for x = 0.15 and is found to be 270 J/kg under a magnetic field change of 5 T and which is around 65 % of that observed for pure gadolinium known as the best material for magnetic refrigeration near room temperature. [ABSTRACT FROM AUTHOR]

The 0.8LaCaSrMnO(LCSMO)/0.2YBaCuO(YBCO) composite was fabricated through a solid-state reaction method. Structural properties, magnetic properties and electrical properties of LCSMO/YBCO composite were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer, and the standard four probe method. The XRD and SEM results indicate that LCSMO and YBCO coexist in the composite without evident reaction between them. The YBCO mostly segregates at the grain boundaries of LCSMO and on the surfaces of the large LCSMO particles. Magnetic measurement reveals that the ferromagnetic order of LCSMO is weakened by addition of YBCO, while the ferromagnetic-paramagnetic transition temperature remains constant. The temperature dependence of resistivity for LCSMO/YBCO composite shows a semiconducting behavior with a gigantic resistivity and disappearance of metal-insulator transition. The resistivity data for the composite has been best fitted by variable range hopping model (VRH) just above T and by small polaron hopping model (SPH) at temperature beyond θ/2. [ABSTRACT FROM AUTHOR]

Structural, magnetic and magnetocaloric properties of LaCaKMnO powder sample elaborated by sol-gel method and annealed at several temperatures (600-1000 °C) were studied. The X-ray diffraction patterns at room temperature show that all our synthesized samples are single phase and crystallize in the distorted orthorhombic system with Pbnm space group. The scanning electron microscopy images evidence a progressive grain growth and consolidation when the annealing temperature increases. The magnetic entropy change Δ S( T), deduced from M( H) isotherms, exhibits a maximum of 4.6 J/kg/K at 310 K under a magnetic applied field change of 5 T for the sample annealed at 1000 °C. The corresponding relative cooling power (RCP) is found to be 260 J/kg which is about 63 % of that obtained in pure gadolinium known as prototype refrigerant at room temperature. [ABSTRACT FROM AUTHOR]

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

A comparative study of the structural, magnetic, and magnetocaloric properties of LaCaKMn0 powder samples elaborated by solid-solid and sol-gel methods is given. The X-ray diffraction patterns at room temperature show that all our synthesized samples elaborated by both methods are single phase. Samples elaborated by solid-solid method crystallize in the orthorhombic structure (Pbnm space group) for x ≤ 0.1 and in the rhombohedral one (R-3C space group) for x= 0.2, while for x = 0.15, the system begins to exhibit both phases with different proportions. The structural transition from Pbnm space group to R-3C one occurs for x > 0.15 for samples elaborated by sol-gel method. Magnetization measurements versus temperature in a magnetic applied field of 50 mT indicate that all our studied samples display a paramagnetic ferromagnetic transition with decreasing temperature. Curie temperature T increases with increasing K content. It increases from 248 K for x = 0 to 310 K for x = 0.2 for samples elaborated by solid-solid method and from 275 K for x = 0 to 320 K for x = 0.2 for samples elaborated by sol-gel route. The maximum of the magnetic entropy change ${\mathrm {\Delta } S}_{M}^{\text {Max}}$ under ΔμH= 5 T is obtained for x = 0.2 sample elaborated by both methods. ${\mathrm {\Delta } \mathrm {S}}_{\mathrm {M}}^{\text {Max}}$ is found to be 5.78 J/kg/K at 305 K and 7.5 J/kg/K at 325 K for sample elaborated by solid-solid and sol gel, respectively. The relative cooling power RCP exhibits a maximum value of 313 J/kg at ΔμH= 5 T for x = 0.05 elaborated by solid-solid method and 300 J/kg at ΔμH= 5 T for x = 0.2 elaborated by sol-gel method. [ABSTRACT FROM AUTHOR]

Magnetic and magnetocaloric properties of polycrystalline (1− x)LaCaMnO/ xCrO(0≤ x ≤ 0.3) composites were investigated. Our composites were elaborated using the solid-state reaction at high temperature. Polycrystalline LaCaMnO (LCMO) was synthesized using the solid-state reaction at high temperature while for CrO we used a commercial product. X-ray diffraction patterns show that the parent compound LaCaMnO is single phase without any detectable impurity and crystallizes in the orthorhombic structure with Pbnm space group. Magnetocaloric effect of our composite materials in the vicinity of the magnetic transition temperatures was investigated. The maximum of the magnetic entropy change $|{\Delta } S_{M}^{\max }|$ is found to be 5.5, 5.12, 4.5, and 3.12 J kg K for x = 0,0.1,0.2, and 0.3 under a magnetic field change of 5 T, respectively. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of the mixed valent cobaltites LaSrAgCoO (0≤ x≤0.15) with perovskite structure have been investigated. X-ray diffraction (XRD) analysis using Rietveld refinement shows that all our samples crystallize in the orthorhombic structure with $R\overline{3}c$ space group. Although the unit cell volume remains almost constant, the Co-O bond length and the Co-O-Co bond angle are sensitive to the Ag addition. All our studied samples undergo a paramagnetic-ferromagnetic transition with decreasing temperature. The zero field cooled (ZFC) and field cooled (FC) magnetization curves at 50 mT of LaSrCoO ( x=0) sample exhibits thermomagnetic irreversibility indicating frustration and competition of both antiferromagnetic and ferromagnetic interactions. It is suggested that Co ions are in the intermediate spin state but Co ions stay in a mixture of intermediate and high spin states. Ag addition leads to dramatic changes in magnetic properties. An interesting result has been obtained for LaSrAgCoO, where the ZFC and FC curves coincide. For LaSrAgCoO ( x=0.15) sample, the observed thermomagnetic irreversibility is much higher than that observed in x=0 sample. Hysteresis loops were recorded for x=0, 0.05, 0.1, and 0.15. The coercitive field is found to increase with Ag content reaching 0.26 T for x=0.15 whereas the remanent magnetization decreases. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the structural, magnetic, and dielectric properties of the compounds La BiSrMnGaO ( x = 0 and 0.06) synthesized with the ceramic method. The structural studies of the compounds showed their indexation in the rhombohedral structure with the R-3C space group. The M( T) investigations under an applied magnetic field of 0.05 T presented a single ferromagnetic-paramagnetic phase transition around the Curie temperature T . Gallium doping with non-magnetic coupling between Ga −O −Gareduces the Curie temperature to lower values: T = 360 K for x = 0 and T = 350 K for x = 0.06. The impedance plot at room temperature ( T = 330 K) appeared as uncompleted semicircular arcs off-centered on the real axis, indicating that the electrical conduction arises from the grain boundaries. The electrical equivalent circuit has been proposed as a parallel combination of grain boundary resistance R and constant phase element impedance (Z) to explain the impedance results. The study of the conductivity with respect to frequency at T = 303 K displayed the reduction of the electron hopping (coulombic interactions) with gallium doping. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of cobaltites with the nominal composition La 0.6−xBi xSr 0.4CoO 3 (0≤ x≤0.15) have been investigated. X-ray diffraction analysis using Rietveld refinement show that all our samples crystallize in the rhombohedral structure. The zero field cooled (ZFC) and field cooled (FC) magnetization curves at 50 mT exhibits thermomagnetic irreversibility signature of short range ferromagnetic interactions in our samples. The ferromagnetic–paramagnetic transition temperature decreases with increasing Bi amount. In the paramagnetic phase, all our synthesized samples obey to the Curie–Weiss law. The Curie–Weiss analysis suggests that the spin state of Co 3+ is IS while Co 4+ ions are in IS for x=0 and LS for x≥0.05. The Bi doping also leads to a weakening in the magnetic moment. The magnetic entropy change exhibits a maximum value which decreases from 2.28 J/kg K for x=0 to 1.24 J/kg K for x=0.15 upon a magnetic field change of 5 T. [ABSTRACT FROM AUTHOR]

The effects of partial substitution of praseodymium by erbium on the structural, magnetic, and magnetocaloric properties of PrErSrMnO (0.0≤ x≤0.2) powder samples have been studied. Our polycrystalline compounds were synthesized by the conventional solid state reaction at high temperature. Rietveld refinement of the X-ray diffraction patterns using Fullprof program shows that all our samples are single phase and crystallize in the orthorhombic structure with the Pnma space group. The unit cell volume decreased with increasing the Er amount. Magnetic measurements show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature T shifts to lower values with increasing Er content. From the magnetization isotherms at different temperatures, magnetic entropy changes Δ S and relative cooling power RCP have been evaluated. The maximum of the magnetic entropy changes for the PrErSrMnO sample is found to be $| \Delta S_{M}^{\max } | = 2.66~\mathrm{J}\,\mathrm{kg}^{-1}\,\mathrm{K}^{-1}$ under a magnetic applied field change of 2 T. [ABSTRACT FROM AUTHOR]

In this paper, we report the structural, magnetic, and magnetocaloric properties of Ni-doped PrCaMnNiO (0≤ y≤0.1) powder samples. Our compounds were synthesized using the solid state reaction method at high temperature. X-ray diffraction analysis using Rietveld refinement show that all our samples are single phase and crystallize in the orthorhombic structure with the Pnma space group. Magnetization measurements versus temperature in a magnetic applied field of 50 mT reveal that Ni doping leads to a paramagnetic-ferromagnetic transition with a Curie temperature increasing from 106 K for y=0.02 to 118.5 K for y=0.1. A large magnetic entropy change |Δ S| has been observed in our doped samples with maximum values around their respective Curie temperatures T. $|\Delta S_{\mathrm{M}}^{\mathrm{max}}|$ is found to be 2 J kg K, 2.96 J kg K and 2.94 J kg K for y=0.02, 0.05, and 0.1, respectively, in a magnetic field change of 5 T. Large relative cooling power (RCP) value of 352.24 J kg is obtained for PrCaMnNiO sample under 5 T. [ABSTRACT FROM AUTHOR]

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

Magnetic and magnetocaloric properties of polycrystalline (1 − x)LaCaMnO/ xFeO(0 ≤ x ≤ 0.09) composites were investigated. Our composites were elaborated using the solidstate reaction at high temperature. Polycrystalline LaCaMnO (LCMO) was synthesized using the solidstate reaction at high temperature while for FeO we used a commercial product. Xray diffraction patterns show that the parent compound LaCaMnO is a single phase without any detectable impurity and crystallizes in the orthorhombic structure with Pbnm space group. Magnetocaloric effect of our composite materials in the vicinity of the magnetic transition temperatures was investigated. The maximum of the magnetic entropy change $\left | {\Delta S}_{M}^{\max }\right |$ is found to be 6.25, 6.37, 6.18 and 5.87 J kg K for x = 0, 0.03, 0.06, and 0.09 under a magnetic field change of 5 T respectively. [ABSTRACT FROM AUTHOR]

Effects of oxygen deficiency on the thermomagnetic properties of LaBaMnO polycrystalline perovskites have been predicted. By the help of the phenomenological model, the temperature dependences of the magnetization for LaBaMnO with δ=0.0, 0.02, 0.05, 0.08, and 0.1 upon 1 T magnetic field were simulated. The behavior of the temperature dependent magnetocaloric effect, in the vicinity of magnetic phase transitions, was investigated. The magnetic entropy change, specific heat, and adiabatic temperature change for several δ were obtained. The values of maximum magnetic entropy change, full-width at half-maximum, and relative cooling power, in 1 T magnetic field variation, were calculated. As the oxygen content increases, the magnetocaloric effect of LaBaMnO, decreases and shifts to room temperature. The results obtained show a strong dependence on the oxygen deficiency of the materials. The magnetocaloric effect of these materials is large and tunable, suggesting a possible technical application of the materials at moderate magnetic fields near room temperature. It is shown that for LaBaMnO, the magnetic entropy change and adiabatic temperature change follows a master curve behavior. [ABSTRACT FROM AUTHOR]

Magnetocaloric properties of LaFeCoSi with the cubic NaZn-type structure were investigated around their Curie temperature T. By the help of the phenomenological model, the magnetization curves for LaFeCoSi at several magnetic fields were simulated. The magnetic entropy change and specific heat are obtained. The values of maximum magnetic entropy change, full-width at half-maximum, and relative cooling power, at several magnetic field variation, were calculated. It is shown that for LaFeCoSi the magnetic entropy change follows an asymmetrical broadening of Δ S peak with increasing field. The maximum magnetic entropy change of this compound is 7.10 JK kg and relative cooling power is 201.37 J/K under a magnetic field of 2 T. The magnetocaloric effect of this material is large and tunable, suggesting a possible technical application of the material at moderate magnetic fields near room temperature. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effect of nonmagnetic YSZ and magnetic FeO addition on the magnetocaloric properties of the LaCaMnO composite. The temperature dependences of the magnetization for pure LCMO and the impurity doped LCMO composite upon 0.1, 0.3, and 1 T magnetic field were simulated. By the help of the phenomenological model, magnetic entropy change and specific heat for magnetic field variation are predicted. The values of maximum magnetic entropy change, full-width at half-maximum, and relative cooling power were calculated at several magnetic fields. The Δ S value is 2.45, 2.39, and 5.58 J kg K at 1 T for pristine LCMO, LCMO/YSZ, and LCMO/FeO, respectively. [ABSTRACT FROM AUTHOR]

Structural and electrical properties of the mixed-valence monovalent doped manganites PrSrKMnO ( x=0, 0.05 and 0.1), prepared using the conventional solid-state synthesis method, have been investigated. Rietveld refinement of the X-ray diffraction patterns at room temperature shows a slight increase in unit cell volume with K content and confirms that all powder samples are single phase and crystallize in the orthorhombic structure with Pnma space group. Electrical resistivity measurements under and without magnetic field show a transition from the metallic to insulating behavior. The electrical conductivity is improved with increasing K content. The resistivity data in metallic region were fitted according to the electron-electron scattering process while in insulating region they were fitted using the small polaron hopping SPH model and Mott's variable range hopping VRH model. [ABSTRACT FROM AUTHOR]

Perovskite-type lanthanum manganite (LaMnO) was synthesized from MnO and LaO precursor powders using the Spark Plasma Sintering technique (SPS). The in situ reaction proceeds in a few minutes at 1000 °C under 50 MPa with a very high heating rate of 100 °C/min. The Rietveld refinement of the X-ray powder diffraction shows that LaMnO sample crystallizes in a perovskite structure of O′-type orthorhombic symmetry with Pbnm space group. After annealing at 1000 °C in air for 10 hrs, the symmetry changes to rhombohedral with R-3c space group. For the as prepared sample, two critical temperature points in the temperature dependence of the ZFC and FC magnetization occurring at 125 K and 145 K are observed. They are suggested to be related to A-type antiferromagnetic Néel temperature and ferromagnetic short range order, respectively. The ferromagnetic component in the annealed sample increases indicating the expected variation in the concentration of Mn and Mn ions, which was attributed to the oxygen stoichiometry effects. [ABSTRACT FROM AUTHOR]