Structural and magnetic properties with large reversible magnetocaloric effect in (La1-xPrx)0.85Ag0.15MnO3 (0.0 ? x ? 0.5) compounds

We report on the effect of Pr doping on structural, magnetic and magnetocaloric properties in (La1-xPrx)0.85Ag0.15MnO3 (0.0 ? x ? 0.5) compounds. The main crystal structure has been studied by performing X-ray diffraction method and structural analysis based on Rietveld method where it is found that although samples at low concentration level (x ? 0.2) have rhombohedral phase (R3c), others (x ? 0.3) have orthorhombic (Pbnm) phase. Scanning electron microscope images show that the average particle size decreases by increasing Pr amount in the main structure. It is observed that the second-order transition temperature from ferromagnetic to paramagnetic phase is dramatically decreased from 262 to 138 K by increasing Pr concentration in (La1-xPrx)0.85Ag0.15MnO3. On the other hand, all samples have also antiferromagnetic coupling observed below TN ~ 50 K. The maximum magnetic entropy change (-?SM)max and relative cooling power values were found in the range of 7.90-2.88 J/kg K and 213.32-153.50 J/kg, respectively, under 50 kOe field change in our samples. It can be argued that particularly the compounds LPAM with x = 0.0, 0.1 and 0.2 are expected to be promising candidate for magnetic refrigeration. © 2016 Informa UK Limited, trading as Taylor & Francis Group

Magnetic field dependence of magnetic coupling in CoCr2O4 nanoparticles

CoCr2O4 spinel nanoparticles synthesized by sol-gel method have been worked extensively by performing structural and magnetic characterization techniques, as well as modeling the experimental results. The microstructure analysis shows that the crystallite size of CoCr2O4 nanoparticles, which are purely crystallized in cubic phase with space group Fd3m, is ~ 75 nm. The grain size distribution determined from scanning electron microscope images indicates that the particles are uniformly formed and distributed homogenously in the structure. A comprehensive magnetic study has been performed by measuring magnetic moment as a function of temperature and external magnetic field. The paramagnetic to ferromagnetic phase transition and non-collinear spiral magnetic transition have been observed in CoCr2O4 nanoparticles at 96 and 27 K, respectively. Interestingly, we observed field-condition shift in lock-in transition which is found as 16 and 8 K for FH and FC, respectively. The exchange bias effect is observed when the CoCr2O4 sample is cooled under magnetic field. The magnitude of exchange bias field decreases with increasing temperature from 5 to 50 K, and it is vanished above 50 K. In addition, we also worked on the magnetic entropy change around the paramagnetic to ferromagnetic phase transition. The magnetic entropy change is found as -0.87 J/kg K under 6 T magnetic field. © 2017 Elsevier B.V.Çukurova ÜniversitesiThis work was partially supported by Çukurova University (Adana/Turkey) under the Project No. of FBA-2017-8082

Effect of Monovalent Cation Doping on Structural, Magnetic, and Magnetocaloric Properties of Pr0.85 A 0.15MnO3 (A = Ag and K) Manganites

A systematic study on the effect of monovalent cation doping on structural, magnetic, and magnetocaloric properties of Pr0.85A0.15MnO3 (A = Ag and K) samples synthesized by a sol-gel method has been carried out. The crystal structure and morphology have been worked by X-ray diffraction (XRD) and scanning electron microscopy (SEM) imaging measurements. The XRD results indicate that both samples have orthorhombic structure. Magnetization versus temperature measurements show that our samples display a ferromagnetic-to-paramagnetic phase transition with increasing temperature. The ferromagnetic-to-paramagnetic phase transition temperature (TC) values were found as 74 and 116 K for Pr0.85Ag0.15MnO3 and Pr0.85K0.15MnO3, respectively. The magnetic entropy changes were evaluated from isothermal magnetization curves measured at various temperatures near TC by steps of 4 K. The values of the magnetic entropy change were determined as 0.99 and 1.39 J kg -1 K -1 for Pr0.85Ag0.15MnO3 and Pr0.85K0.15MnO3 under external field changes of 10 kOe, respectively. © 2016, Springer Science+Business Media New York.FBA-2015-5028, FEF2012D12, FEFBAP/2014-0008This work is supported by the Research Fund of Ad?yaman University, Ad?yaman, Turkey, under grant contract no. FEFBAP/2014-0008 and the Research Fund of ??ukurova University, Adana, Turkey, under grant contract nos. FBA-2015-5028 and FEF2012D12

The structural, superconducting and transport properties of the compounds Y3Ba5Cu8O18 and Y3Ba 5Ca2Cu8O18

This work is related to the structural, superconducting, and transport properties of the compounds Y3Ba5Cu8O 18 and Y3Ba5Ca2Cu8O 18 prepared by the sol-gel method. The influence of the doping of Ca atoms into the compound Y3Ba5Cu8O18 was studied by employing XRD, SEM, AFM, EDX, DTA, TGA, and the electrical resistivity (?), Hall coefficient (R H), Hall mobility (µ H), and magnetoresistance measurements. The XRD spectra showed that Y3Ba5Ca2Cu8O18 almost has the same crystal structure as that of Y3Ba5Cu 8O18, except with some impurity peaks. The resistivity measurements have pointed out that the compounds Y3Ba 5Cu8O18 and Y3Ba5Ca 2Cu8O18 have their T c-onset temperatures at approximately 92.7 and 86.6 K, respectively. The Hall coefficients R H and Hall mobilities µ H have been measured at the 10-300 K temperature interval in a magnetic field of 0.55 T. The signs of R H and µ H are found to be positive for both samples, which indicate that the conduction is p-type in our samples. As expected, the magnetoresistance results clearly demonstrate a considerable decrease of the offset temperatures with increasing magnetic field. © 2011 Springer Science+Business Media, LLC.Acknowledgements This work is supported by the Research Fund of Çukurova University, Adana, Turkey, under grant contracts no. FEF2009BAP10, no. AMYO2009BAP1, no. FEF2009YL30. Dr. Osman Serindag^, Cukurova University, is gratefully acknowledged for the thermal measurements of the present samples. We wish to thank Aydin Eraydin for his help

Effect of boron content on structure and magnetic properties in CoFe2O4 spinel nanocrystals

We study the effect of boron content on the structural and magnetic properties of CoFe2O4 spinel nanocrystallines synthesized by sol-gel method. The crystal structure and phase identification of samples are studied by using X-ray diffraction experiment and Rietveld analysis. Rietveld refinement results reveal that all samples have cubic symmetry with space group Fd3m. The cationic distributions are obtained from Rietveld refinement that boron ions are settled into both tetrahedral and octahedral sites in spinel lattice. The crystallite sizes of samples are found in a range of 47–67 nm that is in the limit of single domain in such structure. All samples show ferromagnetic nature and magnetic transition was not seen in the temperature range of 5–400 K. The magnetic domains are pinned with adding boron ions into the CoFe2O4 spinel structure at low temperatures. Thus, an increment in the propagation field (Hp) and temperature (Tp) by boron content in CoFe2O4 structure is observed. In addition, the saturation magnetization (Ms) normalized by crystal size increases with increasing boron concentration. The temperature dependence of magnetic properties of the samples taken by experimental data are confirmed with the Neel-Arhenius model by adding thermal dependence of magnetocrystalline anisotropy term. The results indicate that boron-doping into the spinel structure enhances ferromagnetic coupling and suppresses super-exchange interaction between tetrahedral (X) and octahedral (Y) sites. © 2018 Elsevier B.V.Çukurova ÜniversitesiThis work was partially supported by Çukurova University (Adana/Turkey) under the Project No. of FBA-2016-6222

Effect of B site partial Ru substitution on structural magnetic and magnetocaloric properties in La0.7Pb0.3Mn1-xRuxO3 (x = 0.0, 0.1 and 0.2) perovskite system

The La0.7Pb0.3Mn1-xRuxO3 (x = 0.0, 0.1 and 0.2) perovskite manganite compounds have been fabricated by solid-state reaction method to investigate structural, magnetic and magnetocaloric properties. All samples are indexed in the Rhombohedral structure with R3?c space group by using the Rietveld refinement method. The Curie temperature decreases from 336 K to 313 K when Ru (x = 0.1) is added to the structure and it becomes 335 K for x = 0.2. Maximum magnetic entropy change and relative cooling power values were calculated as 3.17, 3.15, 3.06 J kg-1 K-1 for 5 T magnetic field change and 214.40, 160.20, 128.38 J kg-1 under 4 T magnetic field change for x = 0.0, 0.1 and 0.2 in La0.7Pb0.3Mn1-xRuxO3, respectively. From the H/M vs M2 plots obtained from isothermal magnetization curves, it is found that all samples exhibit a second-order magnetic phase transition, which shows reversible magnetocaloric effect. Under the light of all observed results, La0.7Pb0.3Mn1-xRuxO3 (x = 0.0, 0.1 and 0.2) perovskite manganite compounds can be considered as candidate materials above room temperature range magnetic cooling systems. © 2019 Elsevier B.V.This work is supported by the Research Fund of Adıyaman University , Adıyaman, Turkey (Under grant contracts no. TFYL/2017-0001 )

Magnetocaloric Properties of La0.85Ag0.15MnO3 and (La0.80Pr0.20)0.85Ag0.15MnO3 Compounds

In this work, the structural and magnetic properties of the polycrystalline La0.85Ag0.15MnO3 (LAM) and (La0.80Pr0.20)0.85Ag0.15MnO3(LPAM) compounds prepared by the sol–gel method were investigated. The structural properties of both polycrystalline compounds were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectrum (EDX) methods. The XRD results showed that both samples crystallized in the hexagonal symmetry with R3¯c$R\overline 3 c$ space group. The SEM images showed that the particles are closely packed with each other, and their size range from 0.5 to 2.0 µm with the average sizes of 1.23 and 1.03 µm, for LAM and LPAM, respectively. From the EDX spectrum, in both compounds, we did not see loss of any integrated elements during the sintering process and no other impurity elements. The magnetic properties were studied by employing temperature M(T) and external magnetic field M(H) dependence of magnetization measurements. Both compounds showed magnetic phase transition from paramagnetic to ferromagnetic phase. With the substitution of Pr for La, the Curie temperature, TC, decreased from 262 to 216 K. At a field change of 5 T, LAM and LPAM showed large magnetic entropy changes of 7.90 and 4.96 J kg-1 K-1, respectively. Furthermore, their relative cooling power (RCP) values were found as 213.32 and 263.02 J kg-1, respectively. These findings make both LAM and LPAM compounds as good candidates for the practical magnetic refrigeration. © 2015, The Author(s)

Structural, Magnetic, and Magnetocaloric Properties of Pb-Substituted La0.7(Te1-xPbx)0.3MnO3 (0.0 ? x ? 0.3) Manganites

The influence of lead substitution on the magnetocaloric properties of La0.7(Te1-xPbx)0.3MnO3 (0.0 ? x ? 0.3) manganites synthesized by solid-state reaction process was studied both by experimental and theoretical modeling. The X-ray diffraction patterns reveal that samples crystallize in the rhombohedral perovskite structure. Thermomagnetic measurements indicate that the magnetic transition temperature increases gradually from 238 to 262 K with increasing Pb amount in the structure. Maximum magnetic entropy changes (?SM) are determined to be 7.16 for x = 0.0 and 4.76 J kg-1 K-1 for x = 0.3. Relative cooling power (RCP) values of samples are ranging between 266.94 and 195.21 J kg-1 at ?H = 5 T. Due to relatively high ?SM and RCP values of the samples, they can be potential materials in magnetic refrigeration applications which work around room temperature. © 2019, Springer Science+Business Media, LLC, part of Springer Nature

Effects of Mn and Gd Co-substituted into ZnO on Structural and Magnetic Properties

We have worked on the structural and magnetic properties of Zn0.99-xMn0.01GdxO?(for x = 0.02, 0.03, and 0.04) compounds prepared by using a sol–gel method. The x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy were used to understand the structural properties of the samples. We observed that co-substitution of Mn (1 %) and Gd (2–4 %) into the ZnO does not change the hexagonal structure. Scanning electron microscope (SEM) images show us that the grain size decreases with the increasing amount of the Gd into the ZnO matrix. The magnetic properties of the samples have been investigated by using magnetic hysteresis and DC susceptibility measurements. The ZMG1 sample shows a weak ferromagnetic behavior at room temperature, whereas the ZMG2 and ZMG3 samples exhibit a paramagnetic nature. Furthermore, it is also found that the magnetizations of the samples decrease with increasing Gd content in the ZnMnO system due to the enhancing interaction between Gd 3+ ions. We summarize that the co-substitution of Mn and Gd into the ZnO generates a room-temperature ferromagnetism, but it still needs more work to obtain strong and high coercivity magnetic loops for applications. © 2014, Springer Science+Business Media New York

Exploration of the superconducting properties of Y3Ba 5Cu8O18 with and without Ca doping by magnetic measurements

The superconducting Y3Ba5Cu8O18 (Y-358) and Y3Ba5Ca2Cu8O 18 (YCa-358) compounds have been synthesized by using the sol-gel method. Hence, the influence of doping of Ca into the compound Y-358 has been studied by comparing the resistivities, DC magnetizations both M(H) and M(T),flux pinning properties, AC susceptibilities and critical current densities of the undoped and doped compounds, at low temperatures. The AC susceptibility and resistivity measurements showed that the superconducting transition temperature, Tc, is suppressed (about 6 K) with the addition of Ca into the main compound. The hysteresis loops of YCa-358 show peak like projecting parts at temperatures below 45 K and around zero applied field that may be due to the local modulation of the composition in YCa-358. Such a behavior has been observed for the first time. The critical current densities, Jc, determined from the hysteresis measurements decrease with the addition of Ca into Y-358. At 15 K, the maximum values of Jc, for the compounds Y-358 and YCa-358 are found to be 8 × 104 A/cm 2 and 4.5 × 104 A/cm2, respectively. The flux pinning force, Fp, calculated from the field dependence of the Jc values shows that the irreversibility line shifts to lower magnetic fields with the doping of Ca into Y-358. Furthermore, the measurements of the inphase and out off components of the ACsusceptibilities clearly demonstrate that the superconducting volume fraction of Y-358 decreases with the addition of Ca. © 2011 Elsevier Masson SAS. All rights reserved.AMYO2009BAP1, FEF2009BAP10, FEF2009YL30This work was supported by Cukurova University under FEF2009BAP10, AMYO2009BAP1, and FEF2009YL30 project numbers. We wish to thank to Mr. Aydin Eraydin for graphical design