Magnetism in DyGd4Si2Ge2
TL;DR: In this article, a rare-earth intermetallic compound DyGd 4 Si 2 Ge 2 having the monoclinic Gd 5 Si 2 Gd 4 Ge 2 -type crystal structure at room temperature has been synthesized and its magnetic susceptibility, electrical resistivity and thermoelectric power are measured in the temperature range 20-300 K.
Abstract: A new rare-earth intermetallic compound, namely DyGd 4 Si 2 Ge 2 having the monoclinic Gd 5 Si 2 Ge 2 -type crystal structure at room temperature has been synthesized and its magnetic susceptibility, electrical resistivity and thermoelectric power are measured in the temperature range 20–300 K. Magnetic susceptibility results reveal a transition from a room temperature paramagnetic phase to a ferromagnetic phase around 65 K ( T C ). Electrical resistivity of DyGd 4 Si 2 Ge 2 is metal-like and has a T 2 dependence at temperatures less than T C . Thermopower displays a change of slope followed by a peak feature just below T C .
Citations
More filters
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 synthesis and crystal growth of quaternary intermetallic compounds based on rare earth metals is discussed, and the importance of electronic and structural feature is highlighted as the key roles in designing these materials for emerging applications.
Abstract: This review highlights the synthesis and crystal growth of quaternary intermetallic compounds based on rare earth metals. In the first part of this review, we highlight briefly about intermetallics and their versatile properties in comparison to the constituent elements. In the next part, we have discussed about various synthesis techniques with more focus on the metal flux technique towards the well shaped crystal growth of novel compounds. In the subsequent parts, several disordered quaternary compounds have been reviewed and then outlined most known ordered quaternary compounds with their complex structure. A special attention has been given to the ordered compounds with structural description and relation to the parent binary and ternary compounds. The importance of electronic and structural feature is highlighted as the key roles in designing these materials for emerging applications.
5 citations
References
More filters
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 Article•
[...]
TL;DR: In this paper, the early days of the Rietveld method are described, along with a retrospective view of its application in various areas of physics, such as X-ray and neutron analysis.
Abstract: Introduction to the Rietveld Method 1. The early days: a retrospective view 2. Mathematical aspects of Rietveld refinement 3. The flow of radiation in a polycrystalline material 4. Data collection strategies: fitting the experiment to the need 5. Background modelling in Rietveld analysis 6. Analytical profile fitting of X-ray powder diffraction profiles in Rietveld analysis 7. Crystal imperfection broadening and peak shape in the Rietveld method 8. Bragg reflection profile shape in X-ray powder diffraction patterns 9. Restraints and constraints in Rietveld refinement 10. Rietveld refinement with time-of-flight powder diffraction data from pulsed neutron sources 11. Combined X-ray and neutron Rietveld refinement 12. Rietveld analysis programs Rietan and Premos and special applications 13. Position - constrained and unconstrained powder-pattern-decomposition methods 14. Ab initio structure solutions with powder diffraction data
3,162 citations
TL;DR: In this article, a giant magnetocaloric effect (ΔSmag) has been discovered in the Gd5(SixGe1−x)4 pseudobinary alloys, where x⩽0.5 is the largest order phase transformation.
Abstract: A giant magnetocaloric effect (ΔSmag) has been discovered in the Gd5(SixGe1−x)4 pseudobinary alloys, where x⩽0.5. For the temperature range between ∼50 and ∼280 K it exceeds the reversible (with respect to alternating magnetic field) ΔSmag for any known magnetic refrigerant material at the corresponding Curie temperature by a factor of 2–10. The two most striking features of this alloy system are: (1) the first order phase transformation, which brings about the large ΔSmag in Gd5(SixGe1−x)4, is reversible with respect to alternating magnetic field, i.e., the giant magnetocaloric effect can be utilized in an active magnetic regenerator magnetic refrigerator; and (2) the ordering temperature is tunable from ∼30 to ∼276 K by adjusting the Si:Ge ratio without losing the giant magnetic entropy change.
657 citations
TL;DR: A study of phase relationships and crystallography in the pseudobinary system Gd5(6Ge1−x)4 revealed: (1) that both terminal binary compounds Gd1Ge3 and Gd2Ge3 crystallize in the Sm5Ge4-type orthorhombic structure, and (2) the appearance of an intermediate (ternary) phase with a monoclinic crystal structure which is similar to both Gd3Si4-Gd5Ge3 compounds.
Abstract: A study of phase relationships and crystallography in the pseudobinary system Gd5(SixGe1−x)4 revealed: (1) that both terminal binary compounds Gd5Si4 and Gd5Ge4 crystallize in the Sm5Ge4-type orthorhombic structure, and (2) the appearance of an intermediate (ternary) phase with a monoclinic crystal structure which is similar to both Gd5Si4 and Gd5Ge4. The formation of the monoclinic phase at 0.24≤x≤0.5 [between Gd5(Si0.96Ge3.03)≅Gd5(Si1Ge3) and Gd5(Si2Ge2)] is probably due to the large difference in bonding characteristics of Si and Ge in the Gd5Si4-Gd5Ge4 pseudobinary system which limits the ability of the mutual substitution of Si for Ge and vice versa without a change of the crystal structure. For the composition Gd5(Si2Ge2) the lattice parameters of the monoclinic structure (space group P1121/a) are a=7.580865), b=14.802(1), c=7.7799(5) A , γ=93.190(4)°. A distinct difference in the magnetic behaviors of the alloys from three different phase regions in this system follows the distinct difference in the crystal structures observed for the alloys from the three phase regions.
245 citations
TL;DR: In this paper, the magnetic phase diagram obtained from the magnetic-field and temperature dependencies of the electrical resistance of a given material was proposed, which is associated with the transition from the low-temperature, low-resistance ferromagnetic orthorhombic to the high-treme, high-sensitivity paramagnetic monoclinic phase.
Abstract: The magnetic field (0 to 4 T) and temperature (5 to 320 K) dependencies of the electrical resistance of ${\mathrm{Gd}}_{5}{(\mathrm{S}\mathrm{i}}_{2}{\mathrm{Ge}}_{2})$ have been measured. Upon heating in zero-magnetic field ${\mathrm{Gd}}_{5}{(\mathrm{S}\mathrm{i}}_{2}{\mathrm{Ge}}_{2})$ undergoes a simultaneous magnetic and crystallographic phase transition at about 276 K. The electrical resistance of ${\mathrm{Gd}}_{5}{(\mathrm{S}\mathrm{i}}_{2}{\mathrm{Ge}}_{2})$ changes drastically and has significant temperature and magnetic-field hystereses. The magnetoresistance has a negative peak of -26% between 274 and 295 K in a 4 T magnetic field, which is associated with the transition from the low-temperature, low-resistance ferromagnetic orthorhombic to the high-temperature, high-resistance paramagnetic monoclinic phase. The increase of the total resistance upon transformation from the magnetically ordered orthorhombic to magnetically disordered monoclinic phase correlates with the differences between the two crystallographic modifications of ${\mathrm{Gd}}_{5}{(\mathrm{S}\mathrm{i}}_{2}{\mathrm{Ge}}_{2}).$ The behavior of the electrical resistance as a function of magnetic field between 262 and 282 K shows the presence of temperature-dependent critical magnetic fields, which can reversibly transform both the magnetic and crystal structures of the material. The magnetic phase diagram obtained from the magnetic-field and temperature dependencies of the electrical resistance of ${\mathrm{Gd}}_{5}{(\mathrm{S}\mathrm{i}}_{2}{\mathrm{Ge}}_{2})$ is proposed.
126 citations