In this review on spin exchanges, written to provide guidelines useful for finding the spin lattice relevant for any given magnetic solid, we discuss how the values of spin exchanges in transition ...metal magnetic compounds are quantitatively determined from electronic structure calculations, which electronic factors control whether a spin exchange is antiferromagnetic or ferromagnetic, and how these factors are related to the geometrical parameters of the spin exchange path. In an extended solid containing transition metal magnetic ions, each metal ion M is surrounded with main-group ligands L to form an ML
polyhedron (typically, n = 3-6), and the unpaired spins of M are represented by the singly-occupied d-states (i.e., the magnetic orbitals) of ML
. Each magnetic orbital has the metal d-orbital combined out-of-phase with the ligand p-orbitals; therefore, the spin exchanges between adjacent metal ions M lead not only to the M-L-M-type exchanges, but also to the M-L…L-M-type exchanges in which the two metal ions do not share a common ligand. The latter can be further modified by d
cations A such as V
and W
to bridge the L…L contact generating M-L…A…L-M-type exchanges. We describe several qualitative rules for predicting whether the M-L…L-M and M-L…A…L-M-type exchanges are antiferromagnetic or ferromagnetic by analyzing how the ligand p-orbitals in their magnetic orbitals (the ligand p-orbital tails, for short) are arranged in the exchange paths. Finally, we illustrate how these rules work by analyzing the crystal structures and magnetic properties of four cuprates of current interest: -CuV
O
, LiCuVO
, (CuCl)LaNb
O
, and Cu
(CO
)
(OH)
.
Superconductivity in (Ba,K)SbO3 Kim, Minu; McNally, Graham M.; Kim, Hun-Ho ...
Nature materials,
06/2022, Letnik:
21, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Abstract
(Ba,K)BiO
3
constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature
T
c
of 30 K arises in proximity to charge density wave order. ...However, the precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO
3
with a positive oxygen–metal charge transfer energy in contrast to (Ba,K)BiO
3
. The parent compound BaSbO
3−
δ
shows a larger charge density wave gap compared to BaBiO
3
. As the charge density wave order is suppressed via potassium substitution up to 65%, superconductivity emerges, rising up to
T
c
= 15 K. This value is lower than the maximum
T
c
of (Ba,K)BiO
3
, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO
3
indicates that strong oxygen–metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors.
We examined what interactions control the sign and strength of the interlayer coupling in van der Waals ferromagnets such as Fe3–x GeTe2, Cr2Ge2Te6, CrI3, and VI3 to find that high-spin orbital ...interactions across the van der Waals gaps are a key to understanding their ferromagnetism. Interlayer ferromagnetic coupling in Fe3–x GeTe2, Cr2Ge2Te6, and CrI3 is governed by the high-spin two-orbital two-electron destabilization, but that in VI3 by the high-spin four-orbital two-electron stabilization. These interactions explain a number of seemingly puzzling observations in van der Waals ferromagnets.
Neutron diffraction studies on magnetic solids composed of axially elongated CoO4X2 (X = Cl, Br, S, Se) octahedra show that the ordered magnetic moments of their high-spin Co2+ (d7, S = 3/2) ions are ...greater than 3 μB, i.e., the spin moment expected for S = 3/2 ions, and increase almost linearly from 3.22 to 4.45 μB as the bond-length ratio r Co–X/r Co–O increases from 1.347 to 1.659 where r Co–X and r Co–O are the Co–X and Co–O bond lengths, respectively. These observations imply that the orbital moments of the Co2+ ions increase linearly from 0.22 to 1.45 μB with increasing the r Co–X/r Co–O ratio from 1.347 to 1.659. We probed this implication by examining the condition for unquenched orbital moment and also by evaluating the magnetic moments of the Co2+ ions based on DFT+U+SOC calculations for those systems of the CoO4X2 octahedra. Our work shows that the orbital moments of the Co2+ ions are essentially quenched and, hence, that the observations of the neutron diffraction studies are not explained by the current theory of magnetic moments. This discrepancy between experiment and theory urges one to check the foundations of the current theory of magnetic moments as well as the current method of neutron diffraction refinements for ordered magnetic structures.
Salt-flux growth of HoCuMg 4 single crystals Reimann, Maximilian Kai; Kremer, Reinhard K; Chen, Da ...
Dalton transactions : an international journal of inorganic chemistry,
2023-Jul-04, 2023-07-04, Letnik:
52, Številka:
26
Journal Article
Recenzirano
Polycrystalline samples of the magnesium-rich intermetallic compounds RECuMg
(RE = Dy, Ho, Er, Tm) were synthesized by reaction of the elements in sealed tantalum ampoules heated in a high-frequency ...induction furnace. Phase purity of the RECuMg
phases was ascertained by powder X-ray diffraction patterns. Well-shaped single crystals of HoCuMg
could be grown in a NaCl/KCl salt flux and the crystal structure was refined from single crystal X-ray diffraction data: TbCuMg
structure-type, space group
,
= 1361.4(2),
= 2039.3(4),
= 384.62(6) pm. The crystal structure of the RECuMg
phases can be understood as a complex intergrowth variant of CsCl and AlB
related slabs. The remarkable crystal chemical motif concerns the orthorhombically distorted bcc-like magnesium cubes with Mg-Mg distances ranging from 306 to 334 pm. At high temperatures DyCuMg
and ErCuMg
are Curie-Weiss paramagnets with paramagnetic Curie-Weiss temperatures of -15 K and -2 K for RE = Dy and Er, respectively. The effective magnetic moments, 10.66
for RE = Dy and 9.65
for RE = Er prove stable trivalent ground states for the rare earth cations. Magnetic susceptibility and heat capacity measurements reveal long-range antiferromagnetic ordering at low temperatures (<21 K). Whereas DyCuMg
exhibits two subsequent antiferromagnetic transitions at
= 21 and 7.9 K which successively remove half of the entropy of a doublet crystal field ground state of Dy, ErCuMg
shows a single, possibly broadened, antiferromagnetic transition at 8.6 K. The successive antiferromagnetic transitions are discussed with respect to magnetic frustration in the tetrameric units present in the crystal structure.
Recent interest in topological semimetals has led to the proposal of many new topological phases that can be realized in real materials. Next to Dirac and Weyl systems, these include more exotic ...phases based on manifold band degeneracies in the bulk electronic structure. The exotic states in topological semimetals are usually protected by some sort of crystal symmetry, and the introduction of magnetic order can influence these states by breaking time-reversal symmetry. We show that we can realize a rich variety of different topological semimetal states in a single material, CeSbTe. This compound can exhibit different types of magnetic order that can be accessed easily by applying a small field. Therefore, it allows for tuning the electronic structure and can drive it through a manifold of topologically distinct phases, such as the first nonsymmorphic magnetic topological phase with an eightfold band crossing at a high-symmetry point. Our experimental results are backed by a full magnetic group theory analysis and ab initio calculations. This discovery introduces a realistic and promising platform for studying the interplay of magnetism and topology. We also show that we can generally expand the numbers of space groups that allow for high-order band degeneracies by introducing antiferromagnetic order.
The new compound Fe3Sb4O6F6 was prepared by hydrothermal synthesis and its crystal structure was determined from single‐crystal X‐ray diffraction data. The synthesis was made under slightly basic ...conditions to prevent oxidation of Fe2+ to Fe3+. The compound crystallizes in the cubic space group I‐43m with separate crystallographic sites for Fe2+ and Sb3+. Fe3Sb4O6F6 is isostructural with M3Sb4O6F6 (M = Co, Ni, Zn). The crystal structure is comprising distorted FeO2F4 octahedra connected via corner sharing at F‐atoms and SbO3 trigonal pyramids that form Sb4O6 units that connect via O‐atoms to the Fe‐atoms. Mössbauer spectroscopy measurements on the hydrothermal synthesis products prove the majority phase contains Fe in the oxidation state +2. Powder X‐ray diffraction suggests that an additional phase of the Mössbauer sample containing Fe3+ can be attributed to FeSbO2F2 as secondary phase. Fe3Sb4O6F6 exhibits antiferromagnetic order below ca. 72 K succeeded by a second magnetic phase transition at ca. 30 K. Strong antiferromagnetic spin‐exchange interaction is attributed to 180° Fe–F–Fe superexchange pathways identified in the crystal structure.
Non‐centrosymmetric Fe3Sb4O6F6 was synthesized by hydrothermal techniques and characterized by X‐ray diffraction data, Mössbauer spectroscopy, and magnetic studies. The compound crystallizes in the cubic space group I‐43m with separate crystallographic sites for Fe2+ and Sb3+, respectively. Fe3Sb4O6F6 exhibits antiferromagnetic order below ca. 72 K succeeded by a second magnetic phase transition at ca. 30 K.
Neutron diffraction studies on magnetic solids composed of axially elongated CoO
X
(X = Cl, Br, S, Se) octahedra show that the ordered magnetic moments of their high-spin Co
(d
,
=
/
) ions are ...greater than 3 μ
, i.e., the spin moment expected for
=
/
ions, and increase almost linearly from 3.22 to 4.45 μ
as the bond-length ratio
/
increases from 1.347 to 1.659 where
and
are the Co-X and Co-O bond lengths, respectively. These observations imply that the orbital moments of the Co
ions increase linearly from 0.22 to 1.45 μ
with increasing the
/
ratio from 1.347 to 1.659. We probed this implication by examining the condition for unquenched orbital moment and also by evaluating the magnetic moments of the Co
ions based on DFT+U+SOC calculations for those systems of the CoO
X
octahedra. Our work shows that the orbital moments of the Co
ions are essentially quenched and, hence, that the observations of the neutron diffraction studies are not explained by the current theory of magnetic moments. This discrepancy between experiment and theory urges one to check the foundations of the current theory of magnetic moments as well as the current method of neutron diffraction refinements for ordered magnetic structures.
V
2
(HCyclal)
2
is prepared by controlled oxidation of vanadium nanoparticles at 50 °C in toluene. The V(0) nanoparticles are synthesized in THF by reduction of VCl
3
with lithium naphthalenide. ...They exhibit very small particle sizes of 1.2 ± 0.2 nm and a high reactivity (
e.g.
with air or water). By reaction of V(0) nanoparticles with the azacrown ether H
4
Cyclal, V
2
(HCyclal)
2
is obtained with deep green crystals and high yield. The title compound exhibits a V(
iii
) dimer (V V: 304.1(1) pm) with two deprotonated HCyclal
3−
ligands as anions. V(0) nanoparticles as well as the sole coordination of V(
iii
) by a crown ether as the ligand and nitrogen as sole coordinating atom are shown for the first time. Magnetic measurements and computational results point to antiferromagnetic coupling within the V(
iii
) couple, establishing an antiferromagnetic spin
S
= 1 dimer with the magnetic susceptibility determined by the thermal population of the total spin ranging from
S
T
= 0 to
S
T
= 2.
V
2
(HCyclal)
2
is prepared by oxidation of V(0) nanoparticles (THF, 50 °C). The V(
iii
) dimer coordinated by HCyclal
3−
anions with nitrogen as sole donor shows antiferromagnetic coupling as shown by magnetic measurements and computation.
The two new ternary amalgams K1–x Rb x Hg11 x = 0.472(7) and Cs3–x Ca x Hg20 x = 0.20(3) represent two different examples of how to create ternary compounds from binaries by statistical atom ...substitution. K1–x Rb x Hg11 is a Vegard-type mixed crystal of the isostructural binaries KHg11 and RbHg11 cubic, BaHg11 structure type, space group Pm3̅m, a = 9.69143(3) Å, Rietveld refinement, whereas Cs3–x Ca x Hg20 is a substitution variant of the Rb3Hg20 structure type cubic, space group Pm3̅n, a = 10.89553(14) Å, Rietveld refinement for which a fully substituted isostructural binary Ca phase is unknown. In K1–x Rb x Hg11, the valence electron concentration (VEC) is not changed by the substitution, whereas in Cs3–x Ca x Hg20, the VEC increases with the Ca content. Amalgams of electropositive metals form polar metal bonds and show “bad metal” properties. By thermal analysis, magnetic susceptibility and resistivity measurements, and density functional theory calculations of the electronic structures, we investigate the effect of the structural disorder introduced by creating mixed-atom occupation on the physical properties of the two new polar amalgam systems.
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