Large magnetic entropy change in nanocrystalline Pr0.7Sr0.3MnO3
04 May 2010-Journal of Applied Physics (American Institute of Physics)-Vol. 107, Iss: 9
TL;DR: In this article, the average crystallite size is calculated using Scherrer formula, and it is found to be ∼25'nm, and the experimentally observed magnetic entropy change of the sample obeys Landau theory of phase transition well.
Abstract: Nanocrystalline Pr0.7Sr0.3MnO3 sample has been prepared by sol-gel method. The room temperature powder x-ray diffraction data show single phase nature of the sample and confirm the cubic crystal structure with Fm3¯m space group. The average crystallite size is calculated using Scherrer formula, and it is found to be ∼25 nm. Transmission electron microscopy image shows that the particles are spherical in shape and the average particle size is ∼35 nm. The sample undergoes ferromagnetic ordering at 235 K (TC) and obeys the Curie–Weiss law in the paramagnetic region. The maximum value of the magnetic entropy change |ΔSM|max is ∼6.3 J kg−1 K−1, and the relative cooling power is ∼385 J kg−1 for a field change of 50 kOe. The Arrott plot confirms that the magnetic ordering is of second order nature. The experimentally observed magnetic entropy change of the sample obeys Landau theory of phase transition well.
TL;DR: In this article, the structural and magnetic properties of the nanoparticles were investigated in detail, and the results suggest that those nanoparticles could be useful for magnetic refrigeration in a broad temperature range.
Abstract: The Ln 0.67 Sr 0.33 MnO 3 (Ln=La, Pr and Nd) nanoparticles were prepared by using the sol–gel method. The structural and magnetic properties of the samples were investigated in detail. The X-ray diffraction (XRD) analyses indicate that the La-doped sample crystalizes in rhombohedral perovskite structure and the Pr-doped and Nd-doped samples are mainly composed of orthorhombic perovskite structure phase. The Curie temperature and saturation magnetization are lowered and the phase transition is broadened by the Pr and Nd substitutions when comparing with the La-doped sample. All the samples exhibit significant magnetocaloric effects in a wide temperature range. Under a field change from 0 to 5 T, the maximum values of isothermal entropy change are found to be 2.49, 1.94 and 0.93 J/kg K for the samples with Ln=La, Pr and Nd, respectively, and the corresponding values of relative cooling power reach 225, 265 and 246 J/kg. The results suggest that those nanoparticles could be useful for magnetic refrigeration in a broad temperature range.
TL;DR: In this paper, the magnetic and magnetocaloric properties of the La0.66Sr0.34MnO3 (LSMO3) compound were investigated using X-ray diffraction results.
Abstract: In this study, the magnetic and the magnetocaloric properties of the La0.66Sr0.34MnO3 (LSMO) compound were investigated. The X-ray diffraction result indicates that the LSMO sample has a single phase of rhombohedral symmetry without any impurity phase. The magnetic study reveals that the specimen La0.66Sr0.34MnO3 exhibits a ferromagnetic-paramagnetic transition at T C ∼ 376 K. Using Arrott plots, the phase transition from ferromagnetic to paramagnetic is found to be of second order. A maximum magnetic entropy change of 1.25 J/kgK has been observed for a low applied magnetic field of 1T. The relative cooling power values exhibit a nearly linear dependence on the applied magnetic field. Moreover, the analysis of the magnetocaloric effect (MCE) using the Landau theory o f phase transitions shows good agreement with the experimental results, confirming the importance of magnetoelastic coupling and electron interactions in the magnetocaloric properties of perovskite manganites. This investigation suggests that La0.66Sr0.34MnO3 can be used as a potential magnetic refrigeration material.
TL;DR: In this article, X-ray diffraction results indicate that the all samples have rhombohedral (R-3c) structure without any impurity phase and the field-cooled magnetization M(T) of all samples show the ferromagnetic behavior below Curie temperature (TC).
Abstract: Polycrystalline La0.65−xPrxSr0.3MnO3 (0.0 ⩽ x ⩽ 0.3) manganite samples were prepared using the conventional solid-state reaction method. The X-ray diffraction result indicates that the all samples have rhombohedral (R-3c) structure without any impurity phase. The field-cooled magnetization M(T) of all samples show the ferromagnetic behavior below Curie temperature (TC). Also, the saturation magnetization and TC of the samples decreases and the transition become broader with increasing the Pr concentration. The Arrott plot analysis reveals the second order of ferromagnetic transition at T = TC for all samples. Magnetic entropy change was evaluated from magnetization isotherms. The magnitude of the isothermal magnetic entropy change is nearly composition independent (1.1 ± 0.15 J kg−1 K−1 for ΔH = 1 T) and relative cooling power lies between 48.85 and 33.10 J/kg for 0.0 ⩽ x ⩽ 0.3. The phenomenon of reversible entropy change and the convenient adjustment of the Curie temperature by Pr doping, make these samples as a possible candidate for magnetic refrigeration at room temperature.
TL;DR: In this paper, the magnetic properties of HoFeO 3 single crystal are investigated along the direction of magnetocaloric properties of a single crystal and magnetic field dependent magnetization isotherms at different temperatures undergo a metamagnetic transition, entropy change as large as 19.2
Abstract: Magnetocaloric properties of HoFeO 3 single crystal are investigated along the direction . Magnetic field dependent magnetization isotherms at different temperatures undergo a metamagnetic transition, entropy change as large as 19.2 J/kg K and 15.8 J/kg K are obtained at 7 T in the vicinity of antiferromagnetic ordering temperature of Ho 3+ and the metamagnetic transition, respectively. The coupling of Ho and Fe spins generates the compensation behavior at 6.5 K, separating the two large magnetic entropy change. Its refrigeration capacity (RC) value, as high as 220 J/kg, is appreciable and can be considered as a promising magnetic refrigerant. New evidence for spin reorientation of Fe 3+ in HoFeO 3 is also provided by the change of magnetic entropy.
TL;DR: In this article, the static magnetic properties and memory and exchange bias effects have been studied in sol-gel prepared La0.67Sr0.33MnO3 (LSMO) nanoparticles.
Abstract: The static magnetic properties and memory and exchange bias effects have been studied in sol-gel prepared La0.67Sr0.33MnO3 (LSMO) nanoparticles. Transmission electron microscopy (TEM) micrographs and static magnetization show log-normal particle and magnetic size distributions with a core-shell structure. Analysis of the magnetization measurements indicates the presence of a magnetic structure with a 7.8 nm core radius and a magnetic dead layer of thickness 1.6 nm in the LSMO nanoparticles, which comprises about 40% of the volume. The disordered spins in the shell freeze at lower temperatures than the core and produce a surface spin glass state exhibiting a weak exchange bias effect. Field cooled and zero-field cooled magnetization measurements have been carried out to study the slow dynamics of the sample and associated magnetic memory effects; the results reveal the superparamagnetic behavior of LSMO nanoparticles described in terms of the magnetic size distribution rather than a superspin glass state.
TL;DR: The discovery of a large magnetic entropy change is reported in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature, attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.
Abstract: Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration1. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.
TL;DR: In this article, a new class of magnetocaloric material, that is, the ferromagnetic perovskite manganites (R1−xMxMnO3, where R=La, Nd, Pr and M=Ca, Sr, Ba, etc.).
Abstract: A thorough understanding of the magnetocaloric properties of existing magnetic refrigerant materials has been an important issue in magnetic refrigeration technology. This paper reviews a new class of magnetocaloric material, that is, the ferromagnetic perovskite manganites (R1−xMxMnO3, where R=La, Nd, Pr and M=Ca, Sr, Ba, etc.). The nature of these materials with respect to their magnetocaloric properties has been analyzed and discussed systematically. A comparison of the magnetocaloric effect of the manganites with other materials is given. The potential manganites are nominated for a variety of large- and small-scale magnetic refrigeration applications in the temperature range of 100–375 K. It is believed that the manganite materials with the superior magnetocaloric properties in addition to cheap materials-processing cost will be the option of future magnetic refrigeration technology.
30 May 2000
TL;DR: In this paper, the fundamental features of CMR Manganites have been discussed, including Spin Dynamics and Electronic Structures, Materials Systematics and Lattice Effects, and Tunnelling Magnetoresistance.
Abstract: 1. Fundamental Features of CMR Manganites 2. Spin Dynamics and Electronic Structures 3. Materials Systematics and Lattice Effects 4. Tunnelling Magnetoresistance.
TL;DR: In this article, an electronic phase transition of the first order, which can be caused by an external magnetic field, was discovered in Nd 1/2 Sr 1 /2 MnO 3, where the hysteretic field region was observed to depend critically on temperature and to drastically expand with a decrease of temperature.
Abstract: An electronic (metal-to-insulator) phase transition of the first order, which can be caused by an external magnetic field, was discovered in Nd 1/2 Sr 1/2 MnO 3 . A clear hysteresis was observed during the increase and decrease of an external magnetic field at a fixed temperature. The hysteretic field region was observed to depend critically on temperature and to drastically expand with a decrease of temperature, perhaps as a result of suppression of the effect of thermal fluctuations on the first-order phase transition. Although it has seldom been observed, this is thought to be a generic feature of the first-order phase transition at low temperatures near 0 kelvin.