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Magnetoresistance measurements have been carried out on single-crystal sample of the transition-metal Zintl compound Eu 14 MnSb 11 . Eu 14 MnSb 11 is the first compound of the Ca 14 -AlSb 11 structure type in which magnetoresistive effects have been measured. Colossal magnetoresistance (CMR) at 92 K and 5 T with ∆F/F(0) ) -36% and at 5 K and 5 T with ∆F/F(0) ) -42% were observed. CMR is observed at the ferromagnetic-paramagnetic phase transition (92 K). A large negative magnetoresistance is observed below the second magnetic transition (15 K) and is attributed to a field-induced antiferromagnetic-ferromagnetic ordering of the Eu 2+ lattice. The MR is highly anisotropic with respect to the crystallographic axes. A sign change in the curvatures of F(H) curves below and above 92 K has been observed, indicating that two different mechanisms are responsible for the magnetic scattering of the carriers in two separate temperature regions.

Treatment of M[N(SiMe(3))(2)](2) (M = Mn, Fe, Co) with various bulky beta-diketimines afforded a variety of new three-coordinate complexes which were characterized by UV-vis, (1)H NMR and IR spectroscopy, magnetic measurements, and X-ray crystallography. Reaction of the beta-diketimine H(Dipp)NC(Me)CHC(Me)N(Dipp) (Dipp(2)N(wedge)NH; Dipp = C(6)H(3)-2,6-Pr(i)(2)) with M[N(SiMe(3))(2)](2) (M = Mn or Co) gave Dipp(2)N(wedge)NMN(SiMe(3))(2) (M = Mn, 1; Co, 3) while the reaction of Fe[N(SiMe(3))(2)](2) with Ar(2)N(wedge)NH (Ar = Dipp, C(6)F(5), Mes, C(6)H(3)-2,6-Me(2), or C(6)H(3)-2,6-Cl(2)) afforded the series of iron complexes Ar(2)N(wedge)NFe[N(SiMe(3))(2)] (Ar = Dipp, 2a; C(6)F(5), 2b; Mes, 2c; C(6)H(3)-2,6-Me(2), 2d; C(6)H(3)-2,6-Cl(2), 2e). This represents a new synthetic route to beta-diketiminate complexes of these metals. The four-coordinate bis-beta-diketiminate complex Fe[N(wedge)N(C(6)F(5))(2)](2), 4, was also isolated as a byproduct from the synthesis of 2b. Direct reaction of the Dipp(2)N(wedge)NLi with CoCl(2) gave the "ate" salt Dipp(2)N(wedge)NCoCl(2)Li(THF)(2), 5, in which the lithium chloride has formed a complex with Dipp(2)N(wedge)NCoCl through chloride bridging. The Fe(III) species Dipp(2)N(wedge)NFeCl(2), 6, was obtained cleanly from the reaction of FeCl(3) with Dipp(2)N(wedge)NLi. Magnetic measurements showed that all the complexes have a high spin configuration. The different substituents in the series of iron complexes 2a-e allowed assignment of their paramagnetically shifted (1)H NMR spectra. The X-ray crystal structures 1-2d and 3 showed that they have a distorted three-coordinate planar configuration at the metals whereas complexes 4-6 have highly distorted four-coordinate geometries.

Large, high quality single crystals of a new Zintl phase, EuIn(2)As(2), have been synthesized from a reactive indium flux. EuIn(2)As(2) is isostructural to the recently reported phase EuIn(2)P(2), and it is only the second reported member of the group of compounds with formula AM(2)X(2) (A = alkali, alkaline earth, or rare earth cation; M = transition or post-transition metal; and X = Group 14 or 15 element) that crystallizes in the hexagonal space group P6(3)/mmc (a = 4.2067(3) A, c = 17.889(2) A and Z = 2). The structure type contains layers of A(2+) cations separated by [M(2)X(2)](2-) layers along the crystallographic c-axis. Crystals of the title compound were mounted for magnetic measurements, with the crystallographic c-axis oriented either parallel or perpendicular to the direction of the applied field. The collective magnetization versus temperature and field data indicate two magnetic exchange interactions near 16 K, one involving Eu(2+)...Eu(2+) intralayer coupling and the other involving Eu(2+)...Eu(2+) coupling between layers. EuIn(2)As(2) is metallic and magnetoresistive, as is the isostructural phosphide, and both compounds have coincident resistivity and magnetic ordering transitions, consistent with the observation of colossal magnetoresistance. Negative colossal magnetoresistance (MR = {[rho(H) - rho(0)]/rho(H)} x 100%) of up to -143% (at T = 17.5 K, H = 5 T) is observed for EuIn(2)As(2), approximately half of that observed for the more resistive phosphide, which has a higher magnetic ordering temperature and local moment coupling strength.

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The heavy electron Kondo liquid is an emergent state of condensed matter that displays universal behavior independent of material details. Properties of the heavy electron liquid are best probed by NMR Knight shift measurements, which provide a direct measure of the behavior of the heavy electron liquid that emerges below the Kondo lattice coherence temperature as the lattice of local moments hybridizes with the background conduction electrons. Because the transfer of spectral weight between the localized and itinerant electronic degrees of freedom is gradual, the Kondo liquid typically coexists with the local moment component until the material orders at low temperatures. The two-fluid formula captures this behavior in a broad range of materials in the paramagnetic state. In order to investigate two-fluid behavior and the onset and physical origin of different long range ordered ground states in heavy electron materials, we have extended Knight shift measurements to URu 2 Si 2 , CeIrIn 5 , and CeRhIn 5 . In CeRhIn 5 we find that the antiferromagnetic order is preceded by a relocalization of the Kondo liquid, providing independent evidence for a local moment origin of antiferromagnetism. In URu 2 Si 2 the hidden order is shown to emerge directly from the Kondo liquid and so is not associated with local moment physics. Our results imply that the nature of the ground state is strongly coupled with the hybridization in the Kondo lattice in agreement with phase diagram proposed by Yang and Pines.nuclear magnetic resonance | heavy fermion | hyperfine couplings C ompetition between different energy scales gives rise to a rich spectrum of emergent ground states in strongly correlated electron materials. In the heavy fermion compounds, a lattice of nearly localized f electrons interacts with a sea of conduction electrons, and depending on the magnitude of this interaction different types of long-range order may develop at low temperatures (1). The Kondo lattice model strives to capture the essential physics of heavy fermion materials by considering the various magnetic interactions between the conduction electron spins, S c , and the local moment spins, S f (2). Different ground states can emerge depending on the relative strengths of the interaction, J, between S c and S f and the intersite interaction, J f f , between the S f spins (3, 4). Much of the physics of the phase diagram is driven by a quantum critical point, which separates long-range ordered ground states from those in which the local moments have fully hybridized with the conduction electrons to form itinerant states with large effective masses and large Fermi surfaces (5). In several materials quantum critical fluctuations give rise to anomalous non-Fermi liquid behavior in various bulk transport and thermodynamic quantities (6-8).In recent years, evidence has emerged that in the high temperature disordered phase the electronic degrees of freedom simultaneously exhibit both itinerant and localized behavior (9). Below a temperature T Ã that marks the onset...

We present magnetotransport and 209 Bi nuclear magnetic resonance (NMR) data on a series of single crystals of Bi2Se3, Bi2Te2Se and CuxBi2Se3 with varying carrier concentrations. The Knight shift of the bulk nuclei is strongly correlated with the carrier concentration via a hyperfine coupling of 27 µeV, which may have important consequences for scattering of the protected surface states. Surprisingly we find that the NMR linewidths and the spin lattice relaxation rate appear to be dominated by the presence of localized spins, which may be related to the presence of Se vacancies.

Synergy between tetrel- and pnictide-based clathrates: synthesis, crystal structure, and transport properties of a Ba8Cu14Ge6P26.