Reversible Magnetocaloric Effect of (La0.8Pr0.2)0.67Ba0.33MnO3 from Direct Measurements

In this study, magnetic and magnetocaloric properties of (La0.8Pr0.2)0.67Ba0.33MnO3 manganite synthesized by sol-gel method were investigated. Under low magnetic field, temperature-dependent zero-field-cooled, field-cooled, and field-heated measurements were performed and the magnetic phase transition temperature corresponding to the sudden drop in magnetization was determined as 200 K. The magnetic entropy change value of the sample is determined as 2.2 J/kgK in 4.8 T magnetic field from isothermal magnetization curves. The adiabatic temperature change (?Tad) of the sample was measured directly using an adiabatic calorimeter and measured as 0.72 K with a field change of 3 T. As a result of cyclic measurement of ?Tad, it is observed that the material has a reversible magnetocaloric effect (MCE) during the application and removal of the field 5 times. This reversible MCE property of the material is important in that it is the most desirable property of potential materials to be used in magnetic cooling systems. © 2019, Springer Science+Business Media, LLC, part of Springer Nature

Impact of small Er rare earth element substitution on magnetocaloric properties of (La0.9Er0.1)0.67Pb0.33MnO3 perovskite

In this work, the effect of Er substitution on the magnetic and magnetocaloric properties has been studied for (La0.9Er0.1)0.67Pb0.33MnO3 perovskite synthesized by the sol-gel procedure. Magnetization measurements performed as a function of both temperature and magnetic field in order to determine magnetic and magnetocaloric properties. The temperature dependence of magnetization measured under 5 mT magnetic field indicate that sample exhibits ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature. The Curie temperature (TC) decreases with Er-doping from 358 K for La0.67Pb0.33MnO3 to 349 K. From the isothermal magnetization measurements taken up to 5T around the TC in 3 K intervals, the magnetic entropy change (?SM) values of the sample have been determined for different magnetic fields. The ?SM max value has been calculated as 0.98, 1.73, 2.33, 2.85 and 3.23 Jkg-1K-1 for 1, 2, 3, 4 and 4.8 T, respectively. The type of magnetic phase transition has been determined as the second order from the slope of Arrott plots. © 2019 Elsevier B.V.This work is supported by the Research Fund of Çukurova University, Adana, Turkey , under grant contracts no. FEF2010D4

Magnetocaloric properties of (La1-xPrx)0.85K0.15MnO3 (x=0.0, 0.1, 0.3 and 0.5) perovskite manganites

In this study, we have investigated the effect of Pr on the structural, magnetic and magnetocaloric properties of (La1-xPrx)0.85K0.15MnO3 (x=0.0, 0.1, 0.3 and 0.5) samples synthesized by sol-gel technique. The XRD patterns of samples for x=0.0 and 0.1 are indexed to rhombohedral structure with hexagonal setting (space group R3¯c) while the samples for x=0.3 and 0.5 crystallized in the orthorhombic structure with space group Pbnm. Magnetization measurements versus temperature in a magnetic field of 250 Oe indicate that all samples show a ferromagnetic to paramagnetic transition with increasing temperature. The Curie temperature, TC, decreases with increasing Pr3+ concentration from 238 K for x=0.0–158 K for x=0.5. We determined the magnetic entropy changes of the samples from M(H) isotherms that were measured around TC. The values of maximum magnetic entropy change were found to be 4.63, 5.22, 2.80 and 2.30 J kg-1 K-1 for x=0.0, 0.1, 0.3 and 0.5 for a field change of 2 T, respectively. For LPKM1 sample, we have also calculated the value of adiabatic temperature change as 3.11 K from the heat capacity and isothermal magnetization measurements under magnetic field of 2 T. © 2016 Elsevier Ltd and Techna Group S.r.l.This work is supported by the Research Fund of Çukurova University , Adana, Turkey, under grant contracts no. FEF2010D12, FBA-2015–4464 and FBA-2015–5028 . The authors thank also Dr. Deniz Takcı for his technical assistance in XRD measurements and Dr. Mark Laver for language assistance

Magnetocaloric effect in (La1-xSmx)0.67Pb0.33MnO3 (0 ? x ? 0.3) manganites near room temperature

Abstract We present an investigation on structure, magnetic and magnetocaloric properties of the perovskite manganites (La1-xSmx)0.67Pb0.33MnO3 (x = 0, 0.1, 0.2, 0.3) synthesized by sol-gel technique. The XRD patterns show that all synthesized samples have reflections typical of the perovskite structure with orthorhombic symmetry. Thermomagnetic measurements showed that all the samples display a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature decreases with increasing Sm content from 358 K for x = 0-286 K for x = 0.3. We determined the isothermal magnetic entropy changes of all the samples from the magnetization measurements and furthermore measured the adiabatic temperature change of the sample for x = 0.3 directly. The results showed that the adiabatic temperature change, determined using together the entropy change and the specific heat and the value obtained by direct temperature change measurements both give 1.3 K for a magnetic field change of 3 T at about 280 K. We also measured the cyclic adiabatic temperature-change of the sample and the results indicate that the sample undergoes a reversible temperature-change on field-cycling which is essential for magnetic refrigeration. © 2015 Elsevier B.V.This work was supported by the Research Fund of Çukurova University, Adana, Turkey , under grant contracts no. FEF2010D4, no. FEF2013BAP29 and Deutsche Forschungsgemeinschaft SPP1599 . We also acknowledge Adana Science and Technology University Research Project Unit (Project Number: MÜHDBF.MLZM.2014-9). The authors acknowledge the Turkish Council of Higher Education for supporting Selda Kılıç Çetin's visit to Duisburg-Essen University. We thank C. Gökhan Ünlü for the support for X-ray refinement

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

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)

Morphological analyses of Hg1-xHoxBa2Ca2Cu3O8+y (0.0 ? x ? 0.20) superconductors fabricated by sol-gel technique

This work reports a systematic study on the morphological properties of the superconducting compounds, Hg1-xHoxBa2Ca2Cu3O8+y with 0.0 ? x ? 0.20, prepared by using the so-called sol-gel method fallowed by a sealed quartz tube synthesis. The analyses of the synthesized products were performed by XRD, AFM, SEM and EDX methods. The results, obtained from the analyses of the XRD and EDX spectra or patterns, and the SEM and AFM images, indicate that the high-Tc Hg-(1223) and Hg-(1234) phases gradually disappear with increasing amounts of Ho. In addition it is observed that, Hg is excluded from the structure with the addition of Ho for Hg. As a result, it has been concluded that the high-Tc phases, Hg-(1223) and Hg-(1234), gradually disappear with increasing amount of Ho content, due to the exclusion of excess amount of Hg from the structures of the samples. This exclusion and observation may be attributed either to the quite different sizes of Ho and Hg ions or to the large HgO powders compared to the sol-gel powders and/or even to the sample preparation method used in this work

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

Magnetic properties of Zn 1-xNi xO (0.25? x ? 0.50) prepared by solid-state reactions

In this study the origin of ferromagnetism in ZnO-based bulk systems has been investigated using Nidoped ZnO samples, Zn 1-xNi xO with 0.25 ? x ? 0.50, prepared by solid-state reactions. The structural characterizations indicated that the Ni 2+ ions almost uniformly distributed in all the samples, and the samples have hexagonal wurtzite structure; however, when x is increased toward 0.50, a new NiO phase is formed. A ferromagnetism (FM) has been observed for all the samples at and below the room temperature. In other words, the room temperature results of (M-H) curves show that the FM observed is intrinsic for all the Ni-doped ZnO samples. However, the saturated magnetizations decrease gradually with increasing Ni concentration. This indicates that, in addition to FM, the excessive doping of Ni in ZnO also causes an antiferromagnetic (AFM) contribution which increases with increasing Ni amount. This result is also supported by the magnetization against temperature measurements. Furthermore, the trend of the acsusceptibility (?) versus temperature curves, measured under an ac-magnetic field of 100 Oe, also support our conclusion about the antiferromagnetic contribution to ferromagnetism in our samples. © Springer Science+Business Media, LLC 2011.Acknowledgements The research work was supported by the Research Fund of Çukurova University, Adana, Turkey, research project no. FEF2009BAP10, no. AMYO2009BAP1, no. FEF2005D16. We wish to thank Aydin Eraydin for his help

Erratum: The structural, superconducting and transport properties of the compounds Y 3Ba 5Cu 8O 18 and Y 3Ba 5Ca 2Cu 8O 18 (Journal of Superconductivity and Novel Magnetism DOI: 10.1007/s10948-011-1192-7)

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