Structure and physical properties of single crystal PrCr2Al20 and CeM2Al20 (M=V, Cr): A comparison of compounds adopting the CeCr2Al20 structure type

Structural trends and itinerant magnetism of the new cage-structured compound HfMn2Zn20

A new cage-structured compound-HfMn2Zn20-belonging to theAB2C20(A, B= transition or rare earth metals, andC= Al, Zn, or Cd) family of structures has been synthesized via the self-flux method. The new compound crystallizes in the space groupFd3¯mwith lattice parametera≈ 14.0543(2) Å (Z= 8) and exhibits non-stoichiometry due to Mn/Zn mixing on the Mn-site and an underoccupied Hf-site. The structure refines to Hf0.93Mn1.63Zn20.37and follows lattice size trends when compared to other HfM2Zn20(M= Fe, Co, and Ni) structures. The magnetic measurements show that this compound displays a modified Curie-Weiss behavior with a transition temperature around 22 K. The magnetization shows no saturation, a small magnetic moment, and near negligible hysteresis, all signs of itinerant magnetism. The Rhodes-Wohlfarth ratio and the spin fluctuation parameters ratio both confirm the itinerant nature of the magnetism in HfMn2Zn20.

Magnetic, specific heat and electrical transport properties of Frank-Kasper cage compounds RTM2Al20 [R = Eu, Gd and La; TM = V, Ti]

Single crystals of Frank-Kasper compounds RTM2Al20 (R  =  Eu, Gd and La; TM  =  V and Ti) were grown by self-flux method and their physical properties were investigated through magnetization (M), magnetic susceptibility (χ), specific heat (C P) and electrical resistivity (ρ) measurements. Powder x-ray diffraction studies and structural analysis showed that these compounds crystallize in the cubic crystal structure with the space group [Formula: see text]. The magnetic susceptibility for the compounds EuTi2Al20 and GdTi2Al20 showed a sudden jump below the Néel temperature T N indicative of plausible double magnetic transition. Specific heat (C P) and electrical resistivity (ρ) measurements also confirm the first-order magnetic transition (FOMT) and possible double magnetic transitions. Temperature variation of heat capacity showed a sharp phase transition and huge C P value for the (Eu/Gd)Ti2Al20 compounds' full width at half-maximum (FWHM) (<0.2 K) which is reminiscent of a first-order phase transition and a unique attribute among RTM2Al20 compounds. In contrast, linear variation of C P is observed in the ordered state for (Eu/Gd)V2Al20 compounds suggesting a λ-type transition. We observed clear anomaly between heating and cooling cycle in temperature-time relaxation curve for the compounds GdTi2Al20 (2.38 K) and EuTi2Al20 (3.2 K) which is indicating a thermal arrest due to the latent heat. The temperature variation of S mag for GdTi2Al20 saturates to a value [Formula: see text] while the other magnetic systems exhibited still lower entropy saturation values in the high temperature limit. [Formula: see text] versus T plot showed a maximum near 27 K for all the compounds indicating the presence of low frequency Einstein modes of vibrations. Resistivity measurements showed that all the samples behave as normal Fermi liquid type compounds and [Formula: see text] due to electron-phonon scattering follows Bloch-Grüneisen-Mott relation in the paramagnetic region.

New heavy-fermion antiferromagnet UPd2Cd20

We succeeded in growing a new high quality single crystal of a ternary uranium compound UPd2Cd20. From the electrical resistivity, magnetization, magnetic susceptibility, and specific heat experiments, UPd2Cd20 is found to be an antiferromagnetic heavy-fermion compound with the Néel temperature [Formula: see text]  =  5 K and exhibits the large electronic specific heat coefficient γ exceeding 500 mJ (K(2)· mol)(-1). This compound is the first one that exhibits the magnetic ordering with the magnetic moments of the U atom in a series of UT2X20 (T: transition metal, X  =  Al, Zn, Cd). UPd2Cd20 shows typical characteristic features in heavy-fermion systems such as a broad maximum in the magnetic susceptibility at [Formula: see text] and a large coefficient A of T (2) term in the resistivity.

Weak hybridization and isolated localized magnetic moments in the compounds CeT₂Cd₂₀ (T = Ni, Pd)

We report the physical properties of single crystals of the compounds CeT2Cd20 (T = Ni, Pd) that were grown in a molten Cd flux. Large separations of  ∼6.7-6.8 Å between Ce ions favor the localized magnetic moments that are observed in measurements of the magnetization. The strength of the Ruderman-Kittel-Kasuya-Yosida magnetic exchange interaction between the localized moments is severely limited by the large Ce-Ce separations and by weak hybridization between localized Ce 4 f and itinerant electron states. Measurements of electrical resistivity performed down to 0.138 K were unable to observe evidence for the emergence of magnetic order; however, magnetically-ordered ground states with very low transition temperatures are still expected in these compounds despite the isolated nature of the localized magnetic moments. Such a fragile magnetic order could be highly susceptible to tuning via applied pressure, but evidence for the emergence of magnetic order has not been observed so far in our measurements up to 2.5 GPa.

Targeted crystal growth of rare Earth intermetallics with synergistic magnetic and electrical properties: structural complexity to simplicity

The single-crystal growth of extended solids is an active area of solid-state chemistry driven by the discovery of new physical phenomena. Although many solid-state compounds have been discovered over the last several decades, single-crystal growth of these materials in particular enables the determination of physical properties with respect to crystallographic orientation and the determination of properties without possible secondary inclusions. The synthesis and discovery of new classes of materials is necessary to drive the science forward, in particular materials properties such as superconductivity, magnetism, thermoelectrics, and magnetocalorics. Our research is focused on structural characterization and determination of physical properties of intermetallics, culminating in an understanding of the structure-property relationships of single-crystalline phases. We have prepared and studied compounds with layered motifs, three-dimensional magnetic compounds exhibiting anisotropic magnetic and transport behavior, and complex crystal structures leading to intrinsically low lattice thermal conductivity. In this Account, we present the structural characteristics and properties that are important for understanding the magnetic properties of rare earth transition metal intermetallics grown with group 13 and 14 metals. We present phases adopting the HoCoGa5 structure type and the homologous series. We also discuss the insertion of transition metals into the cuboctahedra of the AuCu3 structure type, leading to the synthetic strategy of selecting binaries to relate to ternary intermetallics adopting the Y4PdGa12 structure type. We provide examples of compounds adopting the ThMn12, NaZn13, SmZn11, CeCr2Al20, Ho6Mo4Al43, CeRu2Al10, and CeRu4Al16-x structure types grown with main-group-rich self-flux methods. We also discuss the phase stability of three related crystal structures containing atoms in similar chemical environments: ThMn12, CaCr2Al10, and YbFe2Al10. In addition to dimensionality and chemical environment, complexity is also important in materials design. From relatively common and well-studied intermetallic structure types, we present our motivation to work with complex stannides adopting the Dy117Co57Sn112 structure type for thermoelectric applications and describe a strategy for the design of new magnetic intermetallics with low lattice thermal conductivity. Our quest to grow single crystals of rare-earth-rich complex stannides possessing low lattice thermal conductivity led us to discover the new structure type Ln30Ru4+xSn31-y (Ln = Gd, Dy), thus allowing the correlation of primitive volumes with lattice thermal conductivities. We highlight the observation that Ln30Ru4+xSn31-y gives rise to highly anisotropic magnetic and transport behavior, which is unexpected, illustrating the need to measure properties on single crystals.

On the microscopic dynamics of the ‘Einstein solids’ AlV2Al20 and GaV2Al20, and of YV2Al20: a benchmark system for ‘rattling’ excitations

The inelastic response of AV₂Al₂₀ (with A = Al, Ga and Y) was probed by high-resolution inelastic neutron scattering experiments and density functional theory (DFT) based lattice dynamics calculations (LDC).

Crystal growth, structural, electrical, and magnetic properties of mixed-valent compounds YbOs2Al10 and LuOs2Al10

Single crystals of YbOs2Al10 and LuOs2Al10 were grown for the first time using an aluminum self-flux method. The compounds crystallized into a cagelike structure in space group Cmcm, similar to the prototype compound YbFe2Al10. YbOs2Al10 exhibited a mixed-valent nature, as determined by magnetic susceptibility measurements over a wide temperature range from 2 to 900 K, in which the inter-configuration-fluctuation model revealed a broad peak around 400 K. In contrast, LuOs2Al10 displayed Pauli-like paramagnetic behavior over the same temperature range. Both compounds were metallic in nature between 2 and 300 K. The electronic specific heat coefficient of 21.3(2) mJ mol(-1) K(-2) for YbOs2Al10 was determined to be larger than that for LuOs2Al10 [8.9(1) mJ mol(-1) K(-2)], reflecting the mixed-valent nature of the former. First-principles calculations predicted the presence of a mixed-valent state in YbOs2Al10, in agreement with the experimental observations. The novel compound YbOs2Al10 elucidates the evolution of the mixed-valent nature of the Yb-based ternary transition metal aluminides from the 3d to 5d elements.

Effect of the electropositive elements A = Sc, La, and Ce on the microscopic dynamics of AV2Al20

Neutron spectroscopy andab initiocalculations indicate the apparent glass-like lattice thermal conductivityκ_lof the nano-cage compound ScV₂Al₂₀as an effect of phonon renormalization predetermined by the crystal’s ground state properties.