Pauli Paramagnetism Research Articles

Influence of structural disorder on the magnetic properties and electronic structure of YCo2

In this paper the changes of magnetic properties with increasing disorder in the exchange-enhanced Pauli paramagnet ${\mathrm{YCo}}_{2}$ are discussed. The structural disorder is initially introduced by rapid quenching, while further changes on a micro- or nanoscale are caused by a high-pressure torsion (HPT). Values of the magnetic moment determined for the plastically deformed ribbons reach $0.10\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Co}$ atom (for a sample subjected to the deformation at a pressure of 4 GPa) and $0.25\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Co}$ (6 GPa) at 2 K. The magnetic moment arises not only from the surface of nanocrystals but also from volume. Ab initio calculations explained the influence of chemical disorder and different types of structural defects on the electronic structure and magnetic properties of ${\mathrm{YCo}}_{2}$-based Laves phases. The calculated magnetic ground states are in qualitative agreement with experimental results for all considered structures with point defects.

Structure and Bonding of La2NiBi

La2NiBi was synthesized by heating a cold pressed pellet of the elements in a sealed and evacuated silica tube at 1070 K. The structure was determined via powder and single crystal X‐ray diffraction. La2NiBi crystallizes orthorhombically, in the space group Pnma: a = 838.88(6), b = 455.61(11), c = 1210.4(2) pm and V = 0.46261(14) nm3 (wR = 0.1002, 1001 F2 values, 26 variables, Z = 4). La2NiBi represents a higher congener of La2NiSb and adopts a ternary ordered version of the Bi3Ni structure type. Similar to La2NiSb, the nickel atoms form infinite zigzag chains (259 pm Ni–Ni) with trigonal‐prismatic lanthanum coordination. One rectangular face of the lanthanum prism is capped by a bismuth atom (333.08–364.74 pm La–Bi, 281.18 pm Ni–Bi). These zigzag chains run along the b axis. DFT based band structure calculations and DOS representations suggest metallic behavior. This was confirmed via temperature dependent impedance spectroscopic measurements. A Seebeck coefficient of –10 μV·K–1 in the temperature range up to 873 K substantiates this finding. Thermal analyses show that the compound is stable up to 873 K under inert gas conditions and degrades at higher temperatures. The magnetic measurements show almost no grain boundary nickel impurities characterizing La2NiBi as a weak Pauli paramagnet.

Scandium plumbides Sc2Ni2Pb, ScNi1.34Pb and ScCuPb

The crystal structures of three new Sc-based plumbides have been determined from the single-crystal X-ray diffraction data. Sc2Ni2Pb crystallizes with an orthorhombic structure of the Mn2AlB2 - type (space group Cmmm, No. 65, lattice parameters: а = 3.96386(18), b = 13.5551(6), с = 3.35576(11) Å, Z = 2, R1 = 0.0102, wR2 = 0.0249). ScNi1.34Pb forms with a cubic unit cell of the MnCu2Al - type (space group Fm-3m, No. 225, lattice parameter а = 6.25096(12) Å, Z = 4, R1 = 0.0066, wR2 = 0.0141). ScCuPb crystallizes with the hexagonal LiGaGe - type structure (space group P63mc, No. 186, lattice parameters: а = 4.4338(2), с = 6.9500(4) Å, Z = 2, R1 = 0.0383, wR2 = 0.0920). Low-temperature magnetic measurements have revealed that the compound Sc2Ni2Pb is a Pauli paramagnet with the molar magnetic susceptibility of about 2.4 × 10−4 emu/mole.

Synthesis, Characterization, and Electrochemistry of Layered Chalcogenides LiCu Ch ( Ch = Se, Te).

Two novel compounds, LiCu Ch ( Ch = Se or Te), were synthesized by direct reaction between elements in closed ampules inside corundum crucibles. Both compounds are highly air-sensitive and possess an anti-PbClF crystal structure, which contains Cu Ch layer analogues to the Fe[As/Se] layers in Fe-based superconductors. In electrochemical battery cells, Li can be almost completely extracted from LiCuSe, but the reverse reaction is only partly successful and Li2Se and Cu2- xSe are formed instead. LiCuSe exhibits a temperature independent and slightly positive magnetic susceptibility. From 7Li NMR measurements, the activation energy of the Li ion diffusion process is about 0.5 eV but is slightly lower for LiCuTe as compared to LiCuSe. Also, the small and almost temperature independent NMR shifts of the 7Li nucleus indicate the absence of Pauli paramagnetism in these compounds, consistent with a 3 d10 full valence state of the Cu ions.

U8Al19Si6, A Uranium Aluminide Silicide with a Stuffed Supercell Grown from Aluminum Flux

U8Al19Si6 is formed from the reaction of uranium oxide and silicon in aluminum flux. Growth of this material is dependent on the presence of surface hydroxyl groups on alumina in the crucible. The compound forms as large cuboid crystals with a complex new structure that is a cubic stuffed supercell of UAl3 (AuCu3 parent structure type). It features a 4-fold expansion of the unit cell axis and the addition of atoms on two extra positions resulting in Pm3n symmetry. The ordered distribution of aluminum and silicon was determined using single crystal neutron diffraction. The magnetic susceptibility shows temperature independent paramagnetic behavior, while heat capacity measurements are consistent with Fermi liquid characteristics at low temperatures where the Sommerfeld constant is enhanced in comparison to that of a conventional metal. These bulk thermodynamic properties indicate that U8Al19Si6 is an itinerant electron Pauli paramagnet with moderately enhanced mass charge carrier quasiparticles.

The Smaller the Better: Hosting Trivalent Rare-Earth Guests in Cu–P Clathrate Cages

Summary The most striking difference between the trivalent rare-earth cations and their alkali and alkaline-earth peers is the presence of localized 4 f electrons. Placing trivalent rare-earth cations inside fullerene molecules or in between blocks of intermetallics has given rise to a plethora of fascinating properties and materials. A long-sought-after yet undiscovered material is a semiconducting compound with rare-earth cations situated inside the oversized polyhedral cages of a three-dimensional framework. In this work, we present a synthesis of unconventional clathrates, Ba 8−x R x Cu 16 P 30 , with the smallest pentagonal dodecahedral cages encapsulating La 3+ and Ce 3+ . Their composition and crystal structure were unambiguously determined by a combination of synchrotron powder diffraction, time-of-flight neutron powder diffraction, scanning transmission electron microscopy, and electron energy-loss spectroscopy. Our quantum-mechanical calculations and experimental characterizations show that the incorporation of the rare-earth cations significantly enhances hole mobility and reduces hole concentration, resulting in a drastic (700%) increase in the thermoelectric performance.

Crystal structure and magnetic properties of the novel compound Sc5Pd2In4

The novel intermetallic indide Sc5Pd2In4 was synthesized by arc-melting technique, and its crystal structure was determined using the single-crystal X-ray diffraction data (R1 = 0.0233, wR2 = 0.0687). The compound was found to crystallize with an orthorhombic structure of the Lu5Ni2In4 type (space group Pbam), with the lattice parameters: a = 17.4748(7), b = 7.6674(3) and c = 3.3815(2) Å. The magnetic behaviour in Sc5Pd2In4 was studied in the temperature range 1.72–400 K. The compound was established to be a Pauli paramagnet with the molar magnetic susceptibility of about 3.4 × 10−4 emu/mol.

Observation of superconductivity in BaNb2S5

Bulk superconductivity is reported in BaNb2S5 at the transition temperature Tc = 0.85(1) K. The electrical resistivity ρ versus T is metallic with ρ(2 K) = 42.4 µΩ cm. The magnetic susceptibility is paramagnetic, with temperature-independent contributions due to diamagnetism, Pauli paramagnetism, and Van Vleck paramagnetism; a Curie-Weiss contribution appears to be impurity related. Hall effect measurements show that the majority charge carriers are electrons with charge-carrier concentration n(3 K) = 2.40(2) × 1021 cm−3. Specific heat measurements reveal an electronic specific heat coefficient γ = 11.2(1) mJ/mol K2, a Debye temperature ΘD = 126.4(8) K, and an energy gap associated with the superconducting state of Eg = 0.184(4) meV. Measurements of ρ(T) in magnetic field provide the upper critical magnetic field of about 3055(74) Oe as T → 0 K, which was used to estimate the coherence length ξ = 6.21(15) nm. The results allow classification of BaNb2S5 as a Type II, BCS superconductor in the dirty limit.

Ce3−xMgxCo9 : Transformation of a Pauli Paramagnet into a Strong Permanent Magnet

Reducing the reliance on rare-earth elements for permanent magnets is seen as a key technological issue. Enhancing ferromagnetism in a material by adding a magnetic element seems intuitive, but this work reports a rare case where magnetism is enhanced by doping with a $n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c$ component. Starting from the Pauli paramagnet CeCo${}_{3}$, when 45% of Ce atoms are replaced by Mg, the compound becomes a rare-earth-lean ferromagnet that is promising for applications like motors for electric cars. This discovery illustrates that the Stoner mechanism should not be overlooked as a means to induce ferromagnetism by substituting nonmagnetic elements.

Equiatomic rare earth rhodium plumbides RERhPb (RE=Y, La–Nd, Sm, Gd–Lu) with ZrNiAl-type structure

Abstract The equiatomic plumbides RERhPb (RE=Y, La–Nd, Sm, Gd–Lu) were synthesized by induction melting of the elements in sealed niobium ampoules. The samples were characterized by X-ray powder diffraction, confirming their ZrNiAl-type structure, space group P6̅2m. Four structures were refined from single-crystal X-ray diffractometer data: a=769.42(5), c=415.60(3) pm, wR=0.0415, 343 F 2 values, 15 variables for LaRhPb, a=767.91(6), c=369.37(4) pm, wR=0.0798, 284 F 2 values, 15 variables for ErRhPb, a=767.01(8), c=366.21(4) pm, wR=0.0380, 341 F 2 values, 15 variables for YbRhPb and a=766.9(1), c=363.42(6) pm, wR=0.0699, 290 F 2 values, 15 variables for LuRhPb. The RERhPb plumbides contain two crystallographically independent rhodium atoms, both in tricapped trigonal prismatic coordination: Rh1@Pb3 RE 6 and Rh2@RE 6Pb3. Short Rh–Pb distances (277 and 284 pm in ErRhPb) are indicative of covalent Rh–Pb bonding. The crystal chemical details of the RERhPb series are compared with the silver plumbides REAgPb which show different transition metal-lead coloring. Temperature dependent magnetic susceptibility data show Pauli paramagnetism for YRhPb, LaRhPb and LuRhPb. An antiferromagnetic ground state below the Néel temperatures of 13.5, 21.0 and 6.9 K was found for PrRhPb, TbRhPb and DyRhPb, respectively. HoRhPb exhibits Curie-Weiss behavior in the observed temperature range.

Core–Shell Fe–Pt Nanoparticles in Ionic Liquids: Magnetic and Catalytic Properties

The reaction of Fe(CO)5 and Pt2(dba)3 in 1-n-butyl-methylimidazolium tetrafluoroborate (BMIm.BF4), hexafluorophosphate (BMIm.PF6), and bis(trifluoromethanesulfonyl)imide (BMIm.NTf2) under hydrogen affords stable magnetic colloidal core–shell nanoparticles (NPs). The thickness of the Pt shell layer has a direct correlation with the water stability of the anion and increases in the order of PF6 > BF4 > NTf2, yielding the metal compositions Pt4Fe1, Pt3Fe2, and Pt1Fe1, respectively. Magnetic measurements give evidence of a strongly enhanced Pauli paramagnetism of the Pt shell and a partially disordered iron-oxide core with diminished saturation magnetization. The obtained Pauli paramagnetism of the Pt shell is 2 orders of magnitude higher than that of bulk Pt, owing to symmetry breaking at the surface and interface, resulting in a strong increase in the density of states at the Fermi level, and thus to enhanced Pauli susceptibility. Moreover, these ultrasmall NPs showed efficient catalytic activity for the di...

Influence of the electron intrinsic magnetic moment on the transverse dielectric permittivity of degenerate electron gas

Using the linear response theory, the transverse dielectric permittivity of a homogeneous and isotropic system of charged particles is considered. In the ideal gas approximation for the polarization function, an explicit analytical expression for the transverse permittivity of a degenerate electron plasma, which takes into account electron spin, is found. This result describes both the Landau diamagnetism and Pauli paramagnetism in electron plasma. The influence of the electron intrinsic magnetic moment on the spatial and frequency dispersion of the transverse dielectric permittivity of degenerate electron plasma is numerically studied, that is crucial for determining the optical characteristics of plasma.

Sc5Pd4Si6- crystal structure and 29Si/45Sc solid state MAS NMR spectroscopic investigations.

The silicide Sc5Pd4Si6 was synthesized from the elements by arc-melting. Its structure was refined from single crystal X-ray diffractometer data: Immm, Li5Cu3.75P6 type, a = 397.12(6), b = 945.4(1), c = 1314.4(2) pm, wR2 = 0.0245, 578 F2 values and 29 parameters. The palladium atoms have slightly distorted tetrahedral silicon coordination and a condensation of these PdSi4 tetrahedra leads to a two-dimensional substructure which is condensed via Si2 pairs (234 pm Si-Si), forming the [Pd4Si6]δ- polyanionic network. The Sc5Pd4Si6 structure contains three crystallographically independent scandium sites with coordinations Sc1@Pd4Si8Sc6, Sc2@Pd6Si6Sc3 and Sc3@Pd4Si6Sc4. Sc5Pd4Si6 is a Pauli paramagnet with a low susceptibility of 2.9(5) × 10-5 emu mol-1 at room temperature. The 29Si MAS-NMR spectrum confirms the presence of two crystallographically distinct sites in a 2 : 1 ratio. Likewise, the three crystallographic scandium sites are well-differentiated by three 45Sc MAS NMR signals in the expected 2 : 2 : 1 ratio. Unambiguous assignments could be made based on the comparison of the nuclear electric quadrupolar coupling parameters with predicted values from WIEN2k calculations.

Electronic and Magnetic Structures, Magnetic Hyperfine Fields and Electric Field Gradients in UX3 (X = In, Tl, Pb) Intermetallic Compounds

Cubic uranium compounds such as UX3 (X is a non-transition element of groups IIIA or IVA) exhibit highly diverse magnetic properties, including Pauli paramagnetism, spin fluctuation and anti-ferromagnetism. In the present paper, we explore the structural, electronic and magnetic properties as well as the hyperfine fields (HFFs) and electric field gradients (EFGs) with quadrupole coupling constant of UX3 (X = In, Tl, Pb) compounds using local density approximation, Perdew–Burke–Ernzerhof parametrization of generalized gradient approximation (PBE-GGA) including the Hubbard U parameter (GGA + U), a revised version of PBE-GGA that improves equilibrium properties of densely packed solids and their surfaces (PBEsol-GGA), and a hybrid functional (HF-PBEsol). The spin orbit-coupling calculations have been added to investigate the relativistic effect of electrons in these materials. The comparison between the experimental parameters and our calculated structural parameters we confirm the consistency and effectiveness of our theoretical tools. The computed magnetic moments show that magnetic moment increases from indium to lead in the UX3 family, and all these compounds are antiferromagnetic in nature. The EFGs and HFFs, as well as the quadrupole coupling constant of UX3 (X = In, Tl, Pb), are discussed in detail. These properties primarily originate from f and p states of uranium and post-transition sites.

Magnetic properties of the germanides RE 3Pt4Ge6 (RE=Y, Pr, Nd, Sm, Gd–Dy)

Abstract The germanides RE 3Pt4Ge6 (RE=Y, Pr, Nd, Sm, Gd–Dy) have been synthesized by arc-melting of the elements followed by inductive annealing to improve the crystallinity and allow for structural order. The compounds have been studied by powder X-ray diffraction; additionally the structure of Y3Pt4Ge6 has been refined from single-crystal X-ray diffractometer data. It exhibits a (3+1)D modulated structure, indicating isotypism with Ce3Pt4Ge6. The crystal structure can be described as an intergrowth between YIrGe2- and CaBe2Ge2-type slabs along [100]. Temperature-dependent magnetic susceptibility measurements showed Pauli paramagnetism for Y3Pt4Ge6 and Curie-Weiss paramagnetism for Pr3Pt4Ge6 and Nd3Pt4Ge6. Sm3Pt4Ge6 exhibits van Vleck paramagnetism, while antiferromagnetic ordering at T N=8.1(1) K and T N=11.0(1) K is observed for Gd3Pt4Ge6 and Tb3Pt4Ge6, respectively.

Crystal structures and magnetic properties of novel compounds Sc2CoIn and Sc100Co25In7

Crystal structures of two novel scandium-rich ternary compounds forming in the Sc-Co-In system, obtained by arc-melting of pure metals, were determined using X-ray powder diffraction. The structure of Sc2CoIn (space group P4/mmm, а = 3.2887(2), ≿ = 7.1642(4) Å, Z = 1, RI = 5.97%) can be derived from the CsCl-type structure. In turn, the structure of Sc100Co25In7 (space group Fm-3, а = 17.7411(5) Å, Z = 2, RI = 8.08%) is related to the structures of Sc50T13In3 (T = Rh, Ir) and ɛ-Ag7+xMg26-x (x = 0.96). The magnetic properties of both phases were studied at low temperatures down to 1.7 K. The indide Sc2CoIn was found to order antiferromagnetically at 65 K due to the magnetic moments carried on Co atoms. In contrast, Sc100Co25In7 was characterized as a weak Pauli paramagnet.

Gallium-containing Heusler phases ScRh2Ga, ScPd2Ga, TmRh2Ga and LuRh2Ga – magnetic and solid state NMR-spectroscopic characterization

Abstract The gallium-containing Heusler phases ScRh2Ga, ScPd2Ga, TmRh2Ga and LuRh2Ga have been synthesized by arc-melting of the elements followed by different annealing sequences to improve phase purity. The samples have been studied by powder X-ray diffraction. The structures of Lu0.97Rh2Ga1.03 (Fm3̅m, a=632.94(5) pm, wR2=0.0590, 46 F2 values, seven variables) and Sc0.88Rh2Ga1.12 (a=618.91(4) pm, wR2=0.0284, 44 F2 values, six variables) have been refined from single crystal X-ray diffractometer data. Both gallides show structural disorder through Lu/Ga and Sc/Ga mixing. Temperature dependent magnetic susceptibility measurements showed Pauli paramagnetism for ScRh2Ga, ScPd2Ga, and LuRh2Ga and Curie-Weiss paramagnetism for TmRh2Ga. 45Sc and 71Ga solid state MAS NMR spectroscopic investigations of the Sc containing compounds confirmed the site mixing effects typically observed for Heusler phases. The data indicate that the effect of mixed Sc/Ga occupancy is significantly stronger in ScRh2Ga than in ScPd2Ga.

Synthesis and Magnetic Properties of the Boride Series MRh6–nRunB3 (M = Co, Ni; n = 1–5)

Tuning of the magnetic properties of intermetallic materials is increasingly gaining interest in the chemistry community. We report on the successful synthesis and magnetic characterizations of the two new quaternary boride series MRh6–nRunB3 (M = Co, Ni; 1 ≤ n ≤ 5). Powder samples have been synthesized by arc‐melting the elements under purified argon in a water‐cooled copper crucible. The products were characterized by powder X‐ray diffraction through Rietveld refinements as well as EDX measurements. All phases crystallize in the hexagonal Th7Fe3 structure type (space group P63mc, no. 186, Z = 2). In the Co‐based series, the lattice parameters decrease linearly with increasing ruthenium content, whereas in the Ni‐based series they remain nearly constant for the Rh‐rich side then decrease with increasing Ru content. Significant ferromagnetic interactions are observed for the Co‐based series, and they decrease linearly with increasing Ru content with magnetic moments decreasing from 0.74 µB (CoRh5RuB3) to 0.13 µB (CoRhRu5B3) at 5 K and 5 T. Pauli paramagnetism dominates the Ni‐based series.

Anomalous magnetism in hydrogenated graphene

We revisit the problem of local moment formation in graphene due to chemisorption of individual atomic hydrogen or other analogous sp$^3$ covalent functionalizations. We describe graphene with the single orbital Hubbard model, so that the H chemisorption is equivalent to a vacancy in the honeycomb lattice. In order to circumvent artefacts related to periodic unit cells, we use either huge simulation cells of up to $8\times10^5$ sites, or an embedding scheme that allows the modelling of a single vacancy in an otherwise pristine infinite honeycomb lattice. We find three results that stress the anomalous nature of the magnetic moment ($m$) in this system. First, in the non-interacting ($U=0$), zero temperature ($T=0$) case, the $m(B)$ is a continuous smooth curve with divergent susceptibility, different from the step-wise constant function found for a single unpaired spins in a gapped system. Second, for $U=0$ and $T>0$, the linear susceptibility follows a power law $\propto{T}^{-\alpha}$ with an exponent of $\alpha=0.77$ different from conventional Curie's law. For $U>0$, in the mean field approximation, the integrated moment is smaller than $m=1\mu_B$, in contrast with results using periodic unit cells. These three results highlight that the magnetic response of the local moment induced by sp$^3$ functionalizations in graphene is different both from that of local moments in gaped systems, for which the magnetic moment is quantized and follows a Curie law, and from Pauli paramagnetism in conductors, for which a linear susceptibility can be defined at $T=0$.

On the transverse dielectric permittivity of degenerate electron plasma

An explicit analytical expression for the transverse dielectric permittivity of degenerate electron plasma is found in an ideal gas approximation with explicit allowance for the electron spin. The result takes into account the Landau diamagnetism and Pauli paramagnetism in electron plasma.