Peter Klavins

Bio: Peter Klavins is an academic researcher from University of California, Davis. The author has contributed to research in topics: Magnetization & Magnetic susceptibility. The author has an hindex of 26, co-authored 111 publications receiving 1891 citations.

Upper critical field and normal-state properties of single-phase Y1-xPrxBa2Cu3O7- gamma compounds.

Abstract: Substitution of Pr for Y in the Y{sub 1{minus}{ital x}}Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} system depresses {ital T}{sub {ital c}}, with superconductivity disappearing for {ital x}{ge}0.5. The origin of this {ital T}{sub {ital c}} depression is still controversial, as is the valence state of the Pr ion. In order to study these problems, single-phase materials were prepared with {ital x}=0.0, 0.1, 0.2, 0.3, 0.35, 0.4 0.45, 0.5, 0.6, 0.7, 0.9, and 1.0. Under certain annealing conditions, these types of samples will phase separate into YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} and Y{sub 1{minus}{ital x}}Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, showing two transitions in the magnetization, but will still appear single phase from x-ray diffraction. We have overcome this problem through specific annealing conditions of time, temperature, and atmosphere. We find that the superconductivity is strongly suppressed as a function of Pr concentration, with a behavior which is consistent with the classical Abrikosov-Gor'kov pair-breaking theory. The critical fields versus {ital T} show a bell''-shaped behavior, which is consistent with the presence of magnetic pair-breaking interactions. The measured temperature dependence of the critical field, {ital H}{sub {ital c}2} near {ital T}{sub {ital c}}, and the Pauli susceptibility, are used to estimate the physicalmore » parameters {lambda}{sub GL}, {xi}{sub GL}, and {gamma}.« less

Synthesis and Characterization of Three-Coordinate and Related β-Diketiminate Derivatives of Manganese, Iron, and Cobalt

Abstract: Treatment of M{N(SiMe3)2}2 (M = Mn, Fe, Co) with various bulky β-diketimines afforded a variety of new three-coordinate complexes which were characterized by UV−vis, 1H NMR and IR spectroscopy, magnetic measurements, and X-ray crystallography. Reaction of the β-diketimine H(Dipp)NC(Me)CHC(Me)N(Dipp) (Dipp2N∧NH; Dipp = C6H3-2,6-Pri2) with M{N(SiMe3)2}2 (M = Mn or Co) gave Dipp2N∧NMN(SiMe3)2 (M = Mn, 1; Co, 3) while the reaction of Fe{N(SiMe3)2}2 with Ar2N∧NH (Ar = Dipp, C6F5, Mes, C6H3-2,6-Me2, or C6H3-2,6-Cl2) afforded the series of iron complexes Ar2N∧NFe{N(SiMe3)2} (Ar = Dipp, 2a; C6F5, 2b; Mes, 2c; C6H3-2,6-Me2, 2d; C6H3-2,6-Cl2, 2e). This represents a new synthetic route to β-diketiminate complexes of these metals. The four-coordinate bis-β-diketiminate complex Fe{N∧N(C6F5)2}2, 4, was also isolated as a byproduct from the synthesis of 2b. Direct reaction of the Dipp2N∧NLi with CoCl2 gave the “ate” salt Dipp2N∧NCoCl2Li(THF)2, 5, in which the lithium chloride has formed a complex with Dipp2N∧NCoCl throu...

Magnetic properties and negative colossal magnetoresistance of the rare earth Zintl phase EuIn2As2.

Abstract: Large, high quality single crystals of a new Zintl phase, EuIn2As2, have been synthesized from a reactive indium flux. EuIn2As2 is isostructural to the recently reported phase EuIn2P2, and it is only the second reported member of the group of compounds with formula AM2X2 (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 P63/mmc (a = 4.2067(3) A, c = 17.889(2) A and Z = 2). The structure type contains layers of A2+ cations separated by [M2X2]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 Eu2+···Eu2+ intralayer coupling and the other involving Eu2+···Eu2+ coupling between layers....

Colossal Magnetoresistance in the Transition-Metal Zintl Compound Eu14MnSb11

Abstract: Magnetoresistance measurements have been carried out on single-crystal sample of the transition-metal Zintl compound Eu14MnSb11. Eu14MnSb11 is the first compound of the Ca14AlSb11 structure type in which magnetoresistive effects have been measured. Colossal magnetoresistance (CMR) at 92 K and 5 T with Δρ/ρ(0) = −36% and at 5 K and 5 T with Δρ/ρ(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 Eu2+ lattice. The MR is highly anisotropic with respect to the crystallographic axes. A sign change in the curvatures of ρ(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.

Giant magnetoresistance at 300 K in single crystals of La0.65(PbCa)0.35MnO3

Abstract: Giant magnetoresistance (GMR) at 300 K and 5.5 T with ΔR/R(0)=74% was observed in single crystals of La0.65(PbCa)0.35MnO3. The maximum GMR occurs exactly at the ferromagnetic–paramagnetic phase transition temperature (Tc). For T

Electronic structure calculations with dynamical mean-field theory

Abstract: We present a review of the basic ideas and techniques of the spectral density functional theory which are currently used in electronic structure calculations of strongly{correlated materials where the one{electron description breaks down. We illustrate the method with several examples where interactions play a dominant role: systems near metal{insulator transition, systems near volume collapse transition, and systems with local moments.

The puzzle of high temperature superconductivity in layered iron pnictides and chalcogenides

Abstract: The response of the worldwide scientific community to the discovery in 2008 of superconductivity at T c = 26 K in the Fe-based compound LaFeAsO1−x F x has been very enthusiastic. In short order, ot...

MOFs, MILs and more: concepts, properties and applications for porous coordination networks (PCNs)

Abstract: This review (over 380 references) summarizes metal–organic frameworks (MOFs), Materials Institute Lavoisier (MILs), iso-reticular metal–organic frameworks (IR-MOFs), porous coordination networks (PCNs), zeolitic metal–organic frameworks (ZMOFs) and porous coordination polymers (PCPs) with selected examples of their structures, concepts for linkers, syntheses, post-synthesis modifications, metal nanoparticle formations in MOFs, porosity and zeolitic behavior for applications in gas storage for hydrogen, carbon dioxide, methane and applications in conductivity, luminescence and catalysis.

Advanced Thermoelectric Design: From Materials and Structures to Devices

Abstract: The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

Spintronics: a challenge for materials science and solid-state chemistry.

Abstract: Spintronics is a multidisciplinary field involving physics, chemistry, and engineering, and is a new research area for solid-state scientists. A variety of new materials must be found to satisfy different demands. The search for ferromagnetic semiconductors and stable half-metallic ferromagnets with Curie temperatures higher than room temperature remains a priority for solid-state chemistry. A general understanding of structure-property relationships is a necessary prerequisite for the design of new materials. In this Review, the most important developments in the field of spintronics are described from the point of view of materials science.