From molecules to crystal engineering: supramolecular isomerism and polymorphism in network solids.

The purpose of this critical review is to give a representative and comprehensive overview of the arising developments in the field of magnetic metal–organic frameworks, in particular those containing cobalt(II). We examine the diversity of magnetic exchange interactions between nearest-neighbour moment carriers, covering from dimers to oligomers and discuss their implications in infinite chains, layers and networks, having a variety of topologies. We progress to the different forms of short-range magnetic ordering, giving rise to single-molecule-magnets and single-chain-magnets, to long-range ordering of two- and three-dimensional networks (323 references).

Magnetic metal-organic frameworks.

This review discusses instabilities of the Fermi-liquid state of conduction electrons in metals with particular emphasis on magnetic quantum critical points. Both the existing theoretical concepts and experimental data on selected materials are presented; with the aim of assessing the validity of presently available theory. After briefly recalling the fundamentals of Fermi-liquid theory, the local Fermi-liquid state in quantum impurity models and their lattice versions is described. Next, the scaling concepts applicable to quantum phase transitions are presented. The Hertz-Millis-Moriya theory of quantum phase transitions is described in detail. The breakdown of the latter is analyzed in several examples. In the final part experimental data on heavy-fermion materials and transition-metal alloys are reviewed and confronted with existing theory.

http://export.arxiv.org/pdf/cond-mat/0606317

Fermi-liquid instabilities at magnetic quantum phase transitions

Coordination polymer networks with O- and N-donors: What they are, why and how they are made

The literature on open-framework materials has shown numerous examples of porous solids with additional structural, chemical, or physical properties. These materials show promise for applications ranging from sensing, catalysis and separation to multifunctional materials. This critical review provides an up-to-date survey to this new generation of multifunctional open-framework solids. For this, a detailed revision of the different examples so far reported will be presented, classified into five different sections: magnetic, chiral, conducting, optical, and labile open-frameworks for sensing applications. (413 references.)

Old materials with new tricks: multifunctional open-framework materials.

An extensive study of magnetic, thermal, transport, and structural properties of the alloy Y{sub 1{minus}{ital x}}Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital y}} is presented. The endpoints of the alloy series are a high-temperature superconductor Y-Ba-Cu-O and an antiferromagnetic semiconductor (Pr-Ba-Cu-O, {ital T}{sub {ital N}}=17 K). The superconducting transition temperature is reduced with increasing Pr concentration following the Abrikosov-Gorkov pair-breaking curve with critical concentration {ital x}{sub cr}=0.62. Alloying also reduces the Neel temperature approximately linearly with the Y content, and there is a concentration region (0.4{lt}{ital x}{lt}0.6) where antiferromagnetism and superconductivity is suggested to coexist. The specific heat, the susceptibility, the magnetic ordering, and the metal-to-semiconductor transition seen in the resistivity are consistent with the picture that Y{sup 3+} is replaced by Pr{sup 4+} with some degree of valence admixture of the Pr{sup 3+} configuration.

Magnetic ordering and superconductivity in Y1-xPrxBa2Cu3O7-y.

The magnetic order of Pr in nonsuperconducting PrBa{sub 2}Cu{sub 3}O{sub 7} has been studied by specific-heat, susceptibility, and neutron-diffraction measurements. The basic ordering consists of a simple antiferromagnetic arrangement, with a saturated moment of 0.24{mu}{sub {ital B}} and a Neel temperature {ital T}{sub {ital N}} of {similar to}17 K, which is two orders of magnitude higher than expected from either dipolar or Rudeman-Kittel-Kasuya-Yosida interactions alone. The small moment, along with the large value of the low-temperature electronic specific-heat coefficient {gamma} of 196 mJ/mol K{sup 2}, suggests that there is substantial {ital f}-electron character at the Fermi level.

Magnetic order of Pr in PrBa2Cu3O7.

The electrical resistivity of CePd3, La1−xCexPd3, CeRhxPd3−x and Ce Pd3+x systems has been measured from helium temperature to 300 K. The resistivity of pure CePd3 rises from 125 μ Ω cm to 150 μ Ω cm as one cools from 300 K to 100 K. Below 100 K the resisitivity drops dramatically to 10 μ Ω cm at low temperatures. The same qualitative behavior, though less pronounced, is observed in other systems such as CeSn3 which like CePd3 are believed to be of intermediate valence. For x<0.3 the system La1−xCexPd3 is believed to be trivalent. We observe Kondo‐like behavior in this regime. For x near unity we observe that extremely small amounts of La eliminate the rapid fall in resistivity observed below 100 K for pure CePd3. These results suggest that this fall off is due to some type of cooperative Ce ion hehavior. The CeRhxPd3−x system allows one to monitor the effect on resistivity of varying the Ce valence from 3.45 in CePd3 to 4 in CeRh.64Pd2.36. We find that the magnitude of the resistivity rise (upon cooling from 300 K to low temperature) decreases as the Ce valence increases towards four.

Resistive behavior and intermediate valence effects in La1−xCexPd3 and CePd3−xRhx

We report here an entirely new phenomenon, namely magnetic-field-induced superconductivity in Ce${\mathrm{Pb}}_{3}$, a system which at zero field is a heavy-fermion antiferromagnet. This phenomenon is novel in several respects. It is the first reported heavy-fermion magnetic-field-induced superconductor. It is also the first reported magnetic-field-induced superconductor that is also an antiferromagnet. Moreover, it has the simplest crystal structure, ${\mathrm{Cu}}_{3}$Au, of any known heavy-fermion or magnetic-field-induced superconductor.

Observation of magnetic-field-induced superconductivity in a heavy-fermion antiferromagnet: CePb3.

Measurements of the temperature and concentration dependence of the specific heat, magnetic susceptibility, and electrical resistivity for ${\mathrm{Ce}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{La}}_{\mathrm{x}}$${\mathrm{Pb}}_{3}$ are presented. The data scale with the concentration of Ce ions over surprisingly large intervals of x and T. The low-temperature specific heat per Ce ion agrees quantitatively with that of an S=(1/2) Kondo impurity of ${T}_{K}$apeq23.3 K. These results strongly suggest that intersite correlations do not play the expected important role and that the high specific heat \ensuremath{\gamma} reported for ${\mathrm{CePb}}_{3}$ is mainly a manifestation of the single-ion Kondo resonance.

T. Mihalisin

Papers

Magnetic ordering and superconductivity in Y1-xPrxBa2Cu3O7-y.

Magnetic order of Pr in PrBa2Cu3O7.

Resistive behavior and intermediate valence effects in La1−xCexPd3 and CePd3−xRhx

Observation of magnetic-field-induced superconductivity in a heavy-fermion antiferromagnet: CePb3.

Heavy-fermion behavior and the single-ion Kondo model.