Magnetization and neutron diffraction studies on Dy5Si2Ge2
TL;DR: The compound Dy5Si2Ge2 crystallizes in an orthorhombic structure (Sm5Ge4 type, space group Pnma) with a moment value of ∼8μB∕Dy3+ as mentioned in this paper.
Abstract: The compound Dy5Si2Ge2 crystallizes in an orthorhombic structure (Sm5Ge4 type, space group Pnma). Magnetization measurements performed in the temperature range of 2–300 K in applied fields up to 7 T reveal that this compound orders antiferromagnetically at 56 K (TN) but with a positive paramagnetic Curie temperature θP. Magnetization-field isotherms, obtained at 5 K and 20 K, display a field-induced antiferromagnetic to ferromagnetic transition. The magnetization approaches saturation in a field of 6 T with a moment value of ∼8μB∕Dy3+. Neutron diffraction measurements, carried out at 9.2 K, suggest that Dy moments arrange spirally along the a axis giving rise to a canted antiferromagnetic structure. The analysis of neutron diffraction data yields an ordered state magnetic moment of 7.63μBperDy3+ ion.
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TL;DR: In this paper, the magnetic and thermal properties of a compound with a low magnetic field of 0.3m/mT were studied and shown to exhibit a metamagnetic transition (MMT) and a strong magnetocrystalline anisotropy.
Abstract: Magnetic and thermal properties of the compound ${\mathrm{Dy}}_{5}{\mathrm{Si}}_{2}{\mathrm{Ge}}_{2}$ (orthorhombic, ${\mathrm{Sm}}_{5}{\mathrm{Ge}}_{4}$--type) have been studied. This compound orders antiferromagnetically at $56\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ $({T}_{N})$, with a positive paramagnetic Curie temperature $({\ensuremath{\theta}}_{P})$ indicating the presence of competing magnetic interactions. Zero-field-cooled and field-cooled magnetization data obtained in a low field of $5\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$ show irreversibility that starts above ${T}_{N}$, giving rise to a deviation from the paramagnetic Curie-Weiss behavior, in the temperature range of $56--100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Magnetization vs field ($M$ vs $H$) isotherms below $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ display a metamagnetic transition (MMT) and at $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a sharp, martensiticlike, step in magnetization at a critical field of $\ensuremath{\sim}2.9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Heat capacity measurements on this compound in zero applied field exhibit a peak at ${T}_{N}$ which gets subsequently suppressed on application of magnetic fields of $5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ and $9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. The MMT is found to have a dominant role in the associated magnetocaloric effect. The isothermal entropy change $(\ensuremath{\Delta}{S}_{m})$ and the adiabatic temperature change $(\ensuremath{\Delta}{T}_{\mathrm{ad}})$ are found to be $\ensuremath{\sim}8\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕\mathrm{mol}\phantom{\rule{0.2em}{0ex}}\mathrm{K}$ and $\ensuremath{\sim}6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively, for $9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ field change, in the vicinity of ${T}_{N}$. The reversible metamagnetic behavior is envisaged to arise from strong magnetocrystalline anisotropy and/or due to a possible field-induced structural transition as observed in the isostructural ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ compound.
18 citations
TL;DR: In this article, a family of intermetallic materials formed by the rare earth metals (R) and Group 14 elements (T) at the R5T4 stoichiometry is reviewed.
Abstract: Rare earth metals form intermetallic compounds with most of the metallic and semimetallic elements in the periodic table. Due to chemical similarities among 16 of the 17 rare earth elements (Sc frequently stands apart), they often form families of either isostructural or closely related compounds. Despite a long history of research in a broad field of intermetallics, a general theory that enables one to clearly relate composition and structure with physical properties of a multicomponent alloy is still lacking. In this chapter, we review a family of intermetallic materials formed by the rare earth metals (R) and Group 14 elements (T, which can also include certain quantities of Group 13 and 15 elements substituted for Group 14 elements) at the R5T4 stoichiometry. The uniqueness of these compounds lies in their distinctly layered crystallography that can be judiciously controlled by chemistry, processing, and a variety of external triggers including temperature, pressure, and magnetic field. The materials exhibit a host of physical effects related to magnetic and structural transformations that can occur separately or simultaneously. Unlike many other extended families of intermetallic materials, present day understanding of the composition–structure–physical property relationships of R5T4 compounds approaches predictive power, and in this chapter, we show examples of how one can predict some of the interesting physics based on the knowledge of chemical composition and crystal structure of these materials. We hope that this review will further stimulate research in this area and that the science of these materials will be refined and extended in the coming years making the subject much more complete.
12 citations
TL;DR: In this article, the effect of Dy substitution at the Gd-site on the magnetic and electrical transport properties of the giant magnetocaloric effect material, Gd 5 Si 2 Ge 2, has been explored.
Abstract: Effect of Dy substitution at the Gd-site on the magnetic and electrical transport properties of the giant magnetocaloric effect material, Gd 5 Si 2 Ge 2 , has been explored. At room temperature, Dy x Gd 5− x Si 2 Ge 2 ( x ⩽3.5) compounds have the monoclinic Gd 5 Si 2 Ge 2 -type crystal structure (Space group P2 1 /a), while those with x >3.5, have orthorhombic Sm 5 Ge 4 -type structure (Space group Pnma). The Dy substitution contracts the unit cell and also reduces the monoclinic distortion. The compound Gd 5 Si 2 Ge 2 orders ferromagnetically at 276 K; with increasing Dy substitution, the magnetic transition temperature decreases ( T N =56 K for Dy 5 Si 2 Ge 2 ) and the nature of magnetic coupling becomes antiferromagnetic in Dy-rich end. The electrical resistivity shows a marked drop near T C / T N . The thermoelectric power undergoes a slope change in the vicinity of magnetic transition and the signature of phonon and magnon drag effects is observed at low temperatures. Thus progressive Dy substitution in Gd 5 Si 2 Ge 2 leads to a class of materials with interesting magnetic ground states, with magnetic ordering temperatures spanning from 56 to 276 K.
7 citations
TL;DR: A single crystal of rare earth intermetallic compound Dy5Si2Ge2 (Orthorhombic, Space group Pnma) has been prepared by Czochralski method as discussed by the authors.
Abstract: A single crystal of rare earth intermetallic compound Dy5Si2Ge2 (Orthorhombic, Space group Pnma) has been prepared by Czochralski method. Magnetization of Dy5Si2Ge2 single crystal has been measured with magnetic field applied (i) along b axis and (ii) parallel to ac plane. Although a same Neel temperature (TN) of ∼55 K is obtained when 50 Oe field is applied along b axis and in ac plane, the magnitude of magnetization is substantially different. This TN value is close to the antiferromagnetic ordering temperature of polycrystalline Dy5Si2Ge2 as well. The magnetization vs field data at 1.8 K shows an ultra-sharp metamagnetic transition when field is applied along both the directions, in a critical field of about 28 kOe. It is observed that b axis is easy direction of magnetization. Magnetocaloric effect of this Dy5Si2Ge2 crystal has been estimated using magnetization vs field data obtained at various temperatures. A maximum magnetic entropy change (ΔSmmax) of ∼−15.6 J/kg/K has been observed at 22 K with field along b axis and ΔSmmax is ∼−11.2 J/kg/K at 54 K when field is parallel to ac plane, for a field change of 50 kOe. Occurrence of metamagnetic transition at temperatures below TN gives rise to a second peak at ∼22 K in the temperature dependent isothermal magnetic entropy change that leads to the observed large magnetocaloric effect.
2 citations
TL;DR: In this paper, a polycrystalline, Dy0.5Gd4.5Si2Ge2 compound (monoclinic, space group P21/a) has been synthesized and characterized.
Abstract: Polycrystalline, Dy0.5Gd4.5Si2Ge2 compound (monoclinic, space group P21/a) has been synthesized and characterized. This compound orders ferromagnetically at ∼210 K (TC) followed by an antiferromagnetic-like transition at ∼21 K (TN). The electrical resistivity, ρ, follows T2 law in the ferromagnetically ordered state indicating the presence of dominant single magnon scattering. There is a pronounced increase of resistivity in the vicinity of antiferromagnetic transition. Thermoelectric power, S, indicates a slope change near TC and has T3 dependence at low temperatures.
2 citations
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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
TL;DR: The data demonstrate that the giant magnetocaloric effect, observed in low magnetic fields, arises from the amplification of a conventional magnetic entropy-driven mechanism by the difference in the entropies of two phases, borne by the concomitant structural transformation.
Abstract: A massive magnetic-field-induced structural transformation in ${\mathrm{G}\mathrm{d}}_{5}{\mathrm{G}\mathrm{e}}_{4}$, which occurs below 30 K, was imaged at the atomic level by uniquely coupling high-resolution x-ray powder diffraction with magnetic fields up to 35 kOe. In addition to uncovering the nature of the magnetic field induced structural transition, our data demonstrate that the giant magnetocaloric effect, observed in low magnetic fields, arises from the amplification of a conventional magnetic entropy-driven mechanism by the difference in the entropies of two phases, borne by the concomitant structural transformation.
219 citations
TL;DR: In this paper, it was shown that the unusual behavior observed in the near critical Gd 5 (Si x Ge 1-x ) 4 phases is closely related to the stability of the well-defined sub-nanometer thick atomic slabs coupled with the flexibility of their arrangements.
Abstract: The crystal structure, magnetic and other physical properties of the intermetallic Gd 5 (Si x Ge 1-x ) 4 phases are strongly dependent on the Si:Ge ratio (x). Especially intriguing behavior is observed when the chemical composition in this system is near x ≅ 0.5, where small changes in the stoichiometry result in drastic variations in the chemical bonding, electronic structure, crystal structure, and magnetism. Furthermore, the fully reversible magnetic/crystallographic (T C ≅ 270 K) and the irreversible thermoelastic crystallographic (between ∼ 500 and ∼ 750 K) transformations exist near this critical chemical composition. Both of these transformations involve the same two crystallographic modifications: the monoclinic Gd 5 (Si 2 Ge 2 )-type (β) and the orthorhombic Gd 3 Si 4 -type structures (a and γ). First principle calculations of the electronic structure and exchange coupling of these materials are in nearly quantitative agreement with the experiment. It appears that the unusual behavior observed in the near critical Gd 5 (Si x Ge 1-x ) 4 phases is closely related to the stability of the well-defined sub-nanometer thick atomic slabs coupled with the flexibility of their arrangements.
81 citations
TL;DR: In this paper, the magnetic-crystallographic temperature-composition phase diagram has been determined over the whole temperature range (2 -300 K) by means of macroscopic (ac magnetic susceptibility, linear thermal expansion, and resistivity) and microscopic neutron powder diffraction experiments.
Abstract: The different magnetic and crystallographic structures in the series of ${\mathrm{Tb}}_{5}({\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{)}_{4}$ compounds have been studied by means of macroscopic (ac magnetic susceptibility, linear thermal expansion, and resistivity) and microscopic neutron powder diffraction experiments. As a result, the magnetic-crystallographic temperature-composition phase diagram has been determined over the whole temperature range (2--300 K). We have described in detail the origin of the low-temperature magnetic transitions in pure ${\mathrm{Tb}}_{5}{\mathrm{Ge}}_{4}$ and ${\mathrm{Tb}}_{5}{\mathrm{Si}}_{4}$ alloys. Compounds with $x=0.4,$ 0.5, and 0.6 present a monoclinic ${(P112}_{1}/a)$ structure at room temperature. On cooling down, these materials exhibit a first-order crystallographic-magnetic transformation to an orthorhombic (Pnma) canted-ferromagnetic structure. These results constitute an experimental evidence of the strong coupling between crystallographic and magnetic degrees of freedom in the ${\mathrm{Tb}}_{5}({\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{)}_{4}$ compounds.
72 citations
TL;DR: In this paper, the effect of temperature and magnetic field dependent magnetization and heat capacity of polycrystalline polytopes has been measured and the unusual magnetic behavior is discussed in terms of a possible complex magnetic structure at low temperatures.
Abstract: Temperature and magnetic field dependent magnetization and heat capacity of polycrystalline ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ have been measured. In addition to the antiferromagnetic ordering observed at the N\'eel temperature, ${T}_{N}=128\mathrm{K},$ there is a cusp at $\ensuremath{\sim}17.5\mathrm{K}$ in the low-field zero-field cooled (zfc) $M(T)$ curves, below which the zfc and field-cooled (fc) magnetic data exhibit irreversibility. The zfc and fc magnetization data show a complex mixture of reversible and irreversible behaviors at fields between $\ensuremath{\sim}10$ and $\ensuremath{\sim}18\mathrm{kOe},$ which is correlated to the magnetic field induced transitions between the antiferromagnetic (AFM) and the ferromagnetic (FM) states. The initial zfc $M(H)$ data below a certain temperature exhibit two transitions: a discontinuous metamagnetic-like transition and a continuous magnetic moment rotation process. The anomalies in the isofield and isothermal magnetization data indicate a complex magnetic structure at low temperatures, e.g., a complex canted AFM structure. In addition, magnetic field or temperature induced $\mathrm{AFM}\ensuremath{\leftrightarrow}\mathrm{FM}$ transitions occur under certain conditions. The unusual magnetic behavior is discussed in terms of a possible complex magnetic structure at low temperatures and a martensitic-like structural change induced by the magnetic field
62 citations