| 1. |
- Celania, Chris, et al.
(författare)
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R-14(Au, M)(51) (R = Y, La-Nd, Sm-Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, In, Sn, Sb, Bi) : Stability Ranges and Site Preference in the Gd14Ag51 Structure Type
- 2018
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 18:2, s. 993-1001
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Tidskriftsartikel (refereegranskat)abstract
- Twenty new ternary representatives of the Gd14Ag51 structure type have been synthesized within the R-Au-M family (R = Y, La-Nd, Sm-Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, Sn, Sb, Bi) using solid state synthesis techniques. The list of post transition metals (M) involved in the formation of this type of structure could be augmented by five new representatives. All compounds crystallize in the hexagonal space group P6/m (#175) with the unit cell ranges of a = 12.3136(2)-12.918(1) angstrom and c = 8.9967(3)-9.385(1) angstrom, and incorporate different degrees of Au/M mixing. The involvement of the post transition element in the structure varies from one to another compound both qualitatively and quantitatively. A rather significant phase width can be expected for the majority of compounds, however, not without exclusions. The distribution of the post transition metals within the structure has been analyzed via single crystal X-ray diffraction. While the positional disorder of one near-origin Au position is expectable for all compounds due to steric reasons, two specimens show an obvious deviation from the others including another Au position split along the c axis. Possible factors affecting this behavior are discussed.
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| 2. |
- Dhakal, Gyanendra, et al.
(författare)
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Anisotropically large anomalous and topological Hall effect in a kagome magnet
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:16
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Tidskriftsartikel (refereegranskat)abstract
- Recently, kagome materials have become an engrossing platform to study the interplay among symmetry, magnetism, topology, and electron correlation. The latest works on RMn6Sn6 (R = rare-earth metal) compounds have illustrated that this family could be intriguing to investigate various physical phenomena due to large spin-orbit coupling and strong magnetic ordering. However, combined transport and spectroscopic studies in RMn6Sn6 materials are still limited. Here, we report magnetic, magnetotransport, and angle-resolved photoemission spectroscopy measurements of a kagome magnet ErMn6Sn6 that undergoes antiferromagnetic (TN = 345 K) to ferrimagnetic (TC = 68 K) phase transitions in the presence of a field. We observe large anomalous and topological Hall effects serving as transport signatures of the nontrivial Berry curvature. The isothermal magnetization exhibits strong anisotropic nature and the topological Hall effect of the compound depends on the critical field of metamagnetic transition. Our spectroscopic results complemented by theoretical calculations show the multiorbital kagome fermiology. This Letter provides new insight into the tunability and interplay of topology and magnetism in a kagome magnet.
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| 3. |
- Grilli, Davide, et al.
(författare)
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Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)–z : A Symmetric Mirror Homologous Series in the La–Ni–Si System
- 2023
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 62:27, s. 10736-10742
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Tidskriftsartikel (refereegranskat)abstract
- A series of four homologous silicides have been discovered during systematic explorations in the central part of the La–Ni–Si system at 1000 °C. All compounds La12.5Ni28.0Si18.3 (n = 3; a = 28.8686(8), c = 4.0737(2) Å, Z = 3), La22.1Ni39.0Si27.8 (n = 4; a = 20.9340(6), c = 4.1245(2) Å, Z = 1), La32.9Ni49.8Si39.3 (n = 5; a = 24.946(1), c = 4.1471(5) Å, Z = 1), and La44.8Ni66.1Si53.4 (n = 6; a = 28.995(5), c = 4.158(1) Å, Z = 1) crystallize in the hexagonal space group P63/m and can be generalized according to Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)–z with n = 3–6. Their crystal structures are based on AlB2-type building blocks, fused La-centered Ni6Si6 hexagonal prisms, yielding larger oligomeric equilateral domains with the edge size equal to n. The domains extend along the c axis and show checkered ordering of the cationic and anionic parts, while all their atoms are located on mirror planes. Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)–z can be considered as a mirror series to the La-rich La(n+1)(n+2)Nin(n–1)+2Sin(n+1), where an exchange of the formal cationic and anionic sites, i.e., La and Si, occurs. The La–Ni–Si system is the first system where two such analogous series have been observed.
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| 4. |
- Pani, Marcella, et al.
(författare)
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Four ternary silicides in the La-Ni-Si system : from polyanionic layers to frameworks
- 2022
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Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 24:47, s. 8219-8228
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Tidskriftsartikel (refereegranskat)abstract
- The central part of the La–Ni–Si system has been investigated at 800 °C by means of single crystal X-ray diffraction, microscopy and analytical microprobe techniques. The result led to the identification of four new metal-rich silicides: LaNi2Si (Rm, a = 4.0263(3) Å, c = 15.066(2) Å, Z = 3), La2Ni3Si2 (P21/c, a = 6.8789(7) Å, b = 6.2167(3) Å, c = 12.214(1) Å, β = 90.92(1), Z = 4), La3Ni3Si2 (Pnma, a = 7.501(2) Å, b = 14.316(4) Å, c = 6.149(2) Å, Z = 4), La6Ni7Si4 (Pbcm, a = 6.066(1) Å, b = 7.488(1) Å, c = 29.682(5) Å, Z = 4). LaNi2Si belongs to the SrCu2Ga structure type, which is not represented among silicides, while La2Ni3Si2 crystallizes in its own structure type. Both compounds feature layered polyanionic motifs consisting of Ni and Si, which are separated by La. Instead, La6Ni7Si4 and La3Ni3Si2 are characterized by polyanionic networks. The former compound belongs to the Pr6Ni7Si4 structure type, with only two other representatives (Ce and Nd); the latter has been observed only with Rh and Ir. The two structures reveal close structural relationships having multiple identical slabs. Tight-binding electronic structure calculations by linear muffin-tin-orbital methods were performed for LaNi2Si, La2Ni3Si2 and La3Ni3Si2 to gain insights into their structure–bonding relationships. Their band structures suggest a metallic character for all compounds. The overall crystal orbital Hamilton populations are dominated by polar Ni–Si bonds, though homoatomic Ni–Ni and La–Ni(Si) bond contributions are not negligible. The variety of bonding patterns may serve as a logical explanation for the number of discovered compounds in this system as well as for the diversity of the observed structures.
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| 5. |
- Provino, Alessia, et al.
(författare)
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Crystal and Magnetic Structures of the Ternary Ho2Ni0.8Si1.2 and Ho2Ni0.8Ge1.2 Compounds : An Example of Intermetallics Crystallizing with the Zr2Ni1–xP Prototype
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:21, s. 16397-16408
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Tidskriftsartikel (refereegranskat)abstract
- We report two new rare-earth (R) ternary intermetallic compounds—Ho2Ni0.8T1.2 with T = Si and Ge—that correspond to the R5Ni2T3 phase earlier reported to form in Dy–Ni–T and Ho–Ni–T ternary systems. The compounds crystallize in a filled version of the orthorhombic Zr2Ni1–xP-type structure with x = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on Ho2Ni0.8T1.2 with a narrow solid solubility range for the silicide, while the germanide appears to be a line phase. In addition to R = Dy and Ho, R2Ni0.8T1.2 compounds also form for R = Y and Tb, representing the first examples of rare-earth-based compounds adopting the Zr2Ni1–xP structural prototype. Bulk magnetization data reveal the main transitions of the ferrimagnetic or ferromagnetic type at TC = 38 K for Ho2Ni0.8Si1.2 and TC = 37 K for Ho2Ni0.8Ge1.2, which are followed by subsequent magnetic reordering at lower temperatures. Neutron diffraction shows complex magnetic structures below TC with both ferromagnetic and antiferromagnetic components and magnetic propagation vector κ1 = [0, 0, 0]. Below TN ≅ 24 K (22 K) for the silicide (germanide), an additional antiferromagnetic coupling following an incommensurate magnetic propagation vector κ2 = [κx, 0, 0] appears to coexist with the first magnetic structure.
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| 6. |
- Provino, Alessia, et al.
(författare)
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Solubility limits, magnetic and magnetocaloric properties of MoB-type GdCoxNi1−x (0.47 ≤ x ≤ 0.72)
- 2023
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 948
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Tidskriftsartikel (refereegranskat)abstract
- The binary GdNi adopting the orthorhombic CrB-type (oS8, Cmcm) dissolves up to 21 at% Co (GdCo0.42Ni0.58), but when the Co content reaches 23.7 at% the crystal structure of the GdCoxNi1−x phase changes from the orthorhombic CrB-type to the tetragonal MoB-type (tI16, I41/amd). The latter remains stable between 23.7 and 36.0 at% Co (0.47 ≤ xCo ≤ 0.72), and there is a two-phase region compositional gap of ≈ 2.5 at% Co between the two structures. One of the two 8e sites available in the MoB-type structure is filled by Gd atoms, while Co and Ni atoms are randomly occupying the other 8e site. The lattice parameter a increases from 3.9485(1) Å to 3.9591(1) Å, while c decreases from 21.3286(1) Å to 21.2404(1) Å as xCo increases, both following a quadratic trend. As a result, the unit cell volume increases from 332.53(2) Å3 to 332.93(2) Å3 for, respectively, the Co-poor (GdCo0.47Ni0.53) and the Co-rich (GdCo0.72Ni0.28) sides of the solid solution, also following a quadratic trend with a negative deviation of the Zen’s law. The title compound becomes ferromagnetic with TC increasing linearly from 150 K for GdCo0.50Ni0.50 to 171 K for GdCo0.70Ni0.30; linear interpolation leads to TC = 127 K and 174 K for the two ends of the solid solution with xCo = 0.47 and 0.72, respectively. The magnetic susceptibility follows the Curie-Weiss law, indicating a trivalent state of Gd ions, with an effective magnetic moment slightly increasing with the Co content. The magnetocaloric effect, calculated in terms of the isothermal magnetic entropy change, decreases slightly as xCo increases, remaining large in the range 127–174 K.
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| 7. |
- Provino, Alessia, et al.
(författare)
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Stability, Crystal Chemistry, and Magnetism of U2+xN21-xB6 and Nb3-yNi20+yB6 and the Role of Uranium in the Formation of the Quaternary U2-zNbzNi21B6 and U delta Nb3-delta Ni20B6 Systems
- 2019
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:22, s. 15045-15059
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the U-Ni-B and Nb-Ni-B systems to search for possible new heavy fermion compounds and superconducting materials. The formation, crystal chemistry, and physical properties of U2Ni21B6 and Nb3-yNi20+yB6 [ternary derivatives of the cubic Cr23C6-type (cF116, Fm3m)] have been studied; the formation of the hypothetical U3Ni20B6 and Nb2Ni21B6 has been disproved. U2Ni21B6 [a = 10.6701(2) angstrom] crystallizes in the ordered W2Cr21C6-type, whereas Nb3-yNi20+yB6 [a = 10.5842(1) angstrom] adopts the Mg3Ni20B6-type. Ni in U2Ni21B6 can be substituted by U, leading to the solid solution U2-xNi21+yB6 (0 <= x <= 0.3); oppositely, Nb in Nb3Ni20B6 is partially replaced by Ni, forming the solution Nb3-yNi20+yB6 (0 <= y <= 0.5), none of them reaching the limit corresponding to the hypothetically ordered U3Ni20B6 and Nb2Ni21B6. These results prompted us to investigate quaternary compounds U2-zNbzNi21B6 and U6Nb3-delta Ni20B6: strong competition in the occupancy of the 4a and 8c sites by U, Nb, and Ni atoms has been observed, with the 4a site occupied by U/Ni atoms only and the 8c site filled by U/Nb atoms only. U2Ni21B6, U2.3Ni20.7B6, and Nb3Ni20B6 are Pauli paramagnets. Interestingly, Nb2.5Ni20.5B6 shows ferromagnetism with T-c approximate to 11 K; the Curie-Weiss fit gives an effective magnetic moment of 2.78 mu(B)/Ni, suggesting that all Ni atoms in the formula unit contribute to the total magnetic moment. The M(H) data at 2 K further corroborate the ferromagnetic behavior with a saturation moment of 10 mu(B)/fu (approximate to 0.49 mu(B)/Ni). The magnetic moment of Ni at the 4a site induces a moment in all of the Ni atoms of the whole unit cell (32f and 48h sites), with all atoms ordering ferromagnetically at 11 K. Density functional theory (DFT) shows that the formation of U2Ni21B6 and Nb3Ni20B6 is energetically preferred. The various electronic states generating ferromagnetism on Nb2.5Ni20.5B6 and Pauli paramagnetism on U2Ni21B6 and Nb3Ni20B6 have been identified.
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| 8. |
- Provino, Alessia, et al.
(författare)
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Unusual superconductivity in crystallographically disordered RT2−xSn2 compounds
- 2024
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 1000
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Tidskriftsartikel (refereegranskat)abstract
- The discovery of new superconducting materials represents a complementary and crucial tile to shed light on the mechanism controlling the phenomenon of superconductivity. During the search for new superconducting materials, we discovered a new series of intermetallic compounds with the general composition RZn2−xSn2 (R = La, Ce, Pr, Nd). Their formation and crystal structure have been investigated. The Zn content decreases along the series from ≈ 1.50 in LaZn1.50(1)Sn1.98(2) to ≈ 1.32 in NdZn1.321(8)Sn2.01(2), due to the partial occupation of one of the two Zn sites [the Zn1 (2c) site, which from ≈ 50% in the La compound drops to ≈ 42%, ≈ 37% and ≈ 32% in the Ce, Pr and Nd compounds, respectively]. Both the Zn occupation factor and unit cell volume follow the lanthanide contraction. No such compound has been observed with Sm. AC and DC magnetic susceptibility and transport measurements revealed LaZn1.5Sn2 to undergo a sharp superconducting transition at Tc = 5.5 K. In order to search for further possible superconductive homologues, the lanthanum substituted phases La(Zn,T)2–xSn2 (T = Ti, Mn, Fe, Co, Ni, Cu, Pd, Ag, Pt, Au, Cd; x ≈ 0.5) were also prepared. The crystal structure of the ternary compounds is a disordered defective derivative of the tetragonal CaBe2Ge2-type (tP10, P4/nmm), with a partially occupied Zn Wyckoff site and a disordered Sn position. Three related isostructural series, corresponding to three new prototypes, have been identified; they all contain conventional checkered pyramidal layers characteristic of the archetype. The magnetic and transport properties have been measured for some of these substituted quaternary La compounds and we found that superconductivity is preserved in them but in the orthorhombic compounds or when T was a magnetic transition metal (e.g., Ni or Mn). A slight decrease in Tc down to about 4.0 K was detected as a result of the Zn by T atomic substitution.
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