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Journal ArticleDOI

Structural, magnetic, transport and magnetocaloric properties of metamagnetic DyMn0.5Co0.5O3

22 Feb 2012-Journal of Applied Physics (American Institute of Physics)-Vol. 111, Iss: 7
TL;DR: Rietveld refinement of the powder diffraction data revealed that DyMn0.5Co 0.5O3 (DMCO) crystallized in an orthorhombic structure containing distorted Mn/Co−O6 octahedra (sp.gr).
Abstract: Rietveld refinement of the powder diffraction data revealed that DyMn0.5Co0.5O3 (DMCO) crystallized in an orthorhombic structure containing distorted Mn/Co−O6 octahedra (sp.gr = Pnma; a = 5.5922(1) A, b = 7.4987(1) A, c = 5.2606(1) A). Below 85 K, the field cooled magnetization data shows a spontaneous magnetic ordering. The metamagnetic behavior of the sample is evident from the nature of variation of magnetization with applied magnetic field. The field dependent magnetization at 5 K, points out the Mn and Co ions are aligned ferromagnetically, whereas Dy and Mn-Co sublattices are coupled antiferromagnetically. The magnitude of isothermal magnetic entropy change, |ΔSM|max is ∼ 9.30 J kg−1 K−1 in the vicinity of magnetic ordering of Dy3+for the field change of 7 T, is appreciable to consider DyMn0.5Co0.5O3 as a magnetic refrigerant at low temperatures. The temperature variation of electrical resistivity shows the highly insulating nature of the sample.
Citations
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Journal ArticleDOI
TL;DR: The anisotropic MCE in the single-crystal double perovskite Gd2CoMnO6 is investigated, demonstrating the importance of magnetic anisotropy for understanding the MCE and revealing essential clues for exploring suitable magnetic refrigerant compounds aiming at magnetic functional applications.
Abstract: The magnetocaloric effect (MCE) is described by the change in temperature of a material by magnetic field variation and is a crucial subject in magnetism; it is motivated by the desire to enhance energy-efficient magnetic refrigeration for clean technology. Despite the recent discovery of the giant cryogenic MCE in double perovskites, the role of magnetic anisotropy has not yet been clearly discussed, because of the averaging effect of polycrystalline samples. Here, we investigated the anisotropic MCE in the single-crystal double perovskite Gd2CoMnO6. In addition to the ferromagnetic order of the Co2+ and Mn4+ moments, the large Gd3+ moments align below T Gd = 21 K, exhibiting an isotropic nature. Because of the intricate temperature development of magnetically hysteretic behaviour and metamagnetism, the change in magnetic entropy along the c-axis appears to be relatively small. On the contrary, the smaller but almost reversible magnetization perpendicular to the c-axis leads to a large MCE with a maximum entropy change of 25.4 J/kg·K. The anisotropic MCE generates a giant rotational MCE, estimated as 16.6 J/kg·K. Our results demonstrate the importance of magnetic anisotropy for understanding the MCE and reveal essential clues for exploring suitable magnetic refrigerant compounds aiming at magnetic functional applications.

58 citations

Journal ArticleDOI
TL;DR: The synthesized series of the double-perovskite R2CoMnO6 single crystals offer comprehensive information for understanding the roles of mixed-valent magnetic ions and rare earth magnetic moments on the magnetic properties.
Abstract: We have successfully synthesized the series of the double-perovskite R2CoMnO6 (R = rare earth: La to Lu) single crystals and have investigated their magnetic properties. The ferromagnetic order of Co(2+)/Mn(4+) spins emerges mainly along the c axis. Upon decreasing the size of rare earth ion, the magnetic transition temperature decreases linearly from 204 K for La2CoMnO6 to 48 K for Lu2CoMnO6, along with the enhancement of monoclinic distortion. The temperature and magnetic-field dependences of magnetization reveal the various magnetic characteristics such as the metamagnetic transition in R = Eu, the isotropic nature of rare earth moment in R = Gd, and the reversal of magnetic anisotropy in R = Tb and Dy. Our results offer comprehensive information for understanding the roles of mixed-valent magnetic ions and rare earth magnetic moments on the magnetic properties.

44 citations

Journal ArticleDOI
TL;DR: In this article, the crystal structure, magnetic properties, and magnetocaloric effects (MCEs) of polycrystalline oxides were studied using the sol-gel process.

39 citations

Journal ArticleDOI
TL;DR: In this paper, the physical properties of SmFe 0.5Mn0.5O3 complex perovskite samples, synthesized by means of combustion reaction method, were investigated.

38 citations

Journal ArticleDOI
Minki Kim1, Jae Young Moon1, Seung-Hun Oh1, Dong Gun Oh1, Young Jai Choi1, Nara Lee1 
TL;DR: The results based on intricate magnetic correlations and phases in Er2CoMnO6 enrich fundamental and applied research on magnetic materials through the scope of distinct magnetic characteristics in double perovskites.
Abstract: Exploring new magnetic materials is essential for finding advantageous functional properties such as magnetoresistance, magnetocaloric effect, spintronic functionality, and multiferroicity. Versatile classes of double perovskite compounds have been recently investigated because of intriguing physical properties arising from the proper combination of several magnetic ions. In this study, it is observed that the dominant ferrimagnetic phase is coexisted with a minor multiferroic phase in single-crystalline double-perovskite Er2CoMnO6. The majority portion of the ferrimagnetic order is activated by the long-range order of Er3+ moments below TEr = 10 K in addition to the ferromagnetic order of Co2+ and Mn4+ moments arising at TC = 67 K, characterized by compensated magnetization at TComp = 3.15 K. The inverted magnetic hysteresis loop observed below TComp can be described by an extended Stoner-Wohlfarth model. The additional multiferroic phase is identified by the ferroelectric polarization of 0.9 uC/m2 at 2 K. The coexisting ferrimagnetic and multiferroic phases appear to be strongly correlated in that metamagnetic and ferroelectric transitions occur simultaneously. The results based on intricate magnetic correlations and phases in Er2CoMnO6 enrich fundamental and applied research on magnetic materials through the scope of distinct magnetic characteristics in double perovskites.

23 citations

References
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Journal ArticleDOI
TL;DR: An extremely large magnetic entropy change has been discovered in magnetic materials when subjected to a change in the magnetic field as mentioned in this paper, which exceeds the reversible magnetocaloric effect in any known magnetic material by at least a factor of 2.
Abstract: An extremely large magnetic entropy change has been discovered in $\mathrm{Gd}{}_{5}(\mathrm{Si}{}_{2}\mathrm{Ge}{}_{2})$ when subjected to a change in the magnetic field. It exceeds the reversible (with respect to an alternating magnetic field) magnetocaloric effect in any known magnetic material by at least a factor of 2, and it is due to a first order $[\mathrm{ferromagnetic}(\mathrm{I})\ensuremath{\leftrightarrow}\mathrm{ferromagnetic}(\mathrm{II})]$ phase transition at 276 K and its unique magnetic field dependence.

3,561 citations

Journal ArticleDOI
10 Jan 2002-Nature
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.

2,272 citations

Journal ArticleDOI
TL;DR: In this article, a discussion of conduction in glasses containing transition metal ions is presented, and the Miller-Abrahams term and polaron hopping term tend to zero, giving a decreasing slope of the ln p versus 1/T curve.
Abstract: In a discussion of conduction in glasses containing transition metal ions, the following points are stressed: 1. (a) The process is similar to “impurity conduction” in doped and compensated semi-conductors. 2. (b) There should be two terms in the activation energy, the Miller-Abrahams term and a polaron hopping term. 3. (c) Both terms should tend to zero, giving a decreasing slope of the ln p versus 1/T curve, as T → 0. 4. (d) The Heikes-Ure formula for the thermopower is discussed and a tentative explanation given of the difference between vanadium- and iron-containing glasses.

2,211 citations

Journal ArticleDOI
24 Sep 1998-Nature
TL;DR: In this article, it was shown that the atmosphere of solid planets is capable of exerting dynamic pressure on their surfaces, thereby exciting free oscillations with amplitudes large enough to be detected by modern broad-band seismographs.
Abstract: Seismology provides a powerful tool for probing planetary interiors1,2, but it has been considered inapplicable to tectonically inactive planets where earthquakes are absent. Here, however, we show that the atmospheres of solid planets are capable of exerting dynamic pressure on their surfaces, thereby exciting free oscillations with amplitudes large enough to be detected by modern broad-band seismographs. Order-of-magnitude estimates of these forces give similar amplitudes of a few nanogals for the Earth, Venus and Mars despite widely varying atmospheric and ambient conditions. The amplitudes are also predicted to have a weak frequency dependence. Our analysis of seismograms, recorded continuously from 1992 to 1993 at 13 globally distributed stations, shows strong evidence for continuously excited fundamental-mode free oscillations on the Earth. This result, together with other recent studies3,4,5, is consistent with our estimate of atmospheric forcing and we therefore propose that it may be possible to detect atmospheric excitation of free oscillations on Venus and Mars as well.

1,048 citations

Journal ArticleDOI
TL;DR: In this article, a survey of microscopic factors determining the coexistence of magnetite and ferroelectricity is given, and different possible routes to combine them in one material are discussed, in particular, the role of the occupation of d-states in transition metal perovskites, possible role of spiral magnetic structures, and the mechanism of ferro electricity in magnetic systems due to combination of site-centered and bond-centred charge ordering.

812 citations