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ABSTRACT: We report on single crystal nuclear magnetic resonance spectroscopy for 63Cu at the Cu(5) sites in the heavy-fermion paramagnet CeCu6 for constant external magnetic field strength (7T) applied along the “hardest” magnetic direction b and varied temperature (5 − 100K). The transferred field coupling constant α
b
(5) = + 3.40(31) kOe/μ
B
is derived from the van Vleck like paramagnetic line shift. These results establish the predominance of anisotropic spin
and orbital polarization acting on the Cu sites neighbouring the Ce 4f local moment. Because magnetically induced electric quadrupolar interaction at this Cu site is not unusually enhanced, we
conclude that the exchange polarization mechanism at the Ce site is the source of the observed anisotropy. Impact of the substitution
of Cu(2) by Au on the Ce3+ single-ion ground state properties and magnetic characteristics of CeCu6-x
Au
x
is discussed.
Journal of Low Temperature Physics 04/2007; 147(3):111-122. · 1.19 Impact Factor
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ABSTRACT: Reaction of lithium tetrachloromanganate(II) with N-n-butyldiethanolamine H2L3 (3) in the presence of LiH leads to the formation of wheel-shaped, mixed-valent heptanuclear, neutral complex {MnII subset[MnII2MnIII4Cl6(L3)6]} (4). The manganese wheel crystallizes in the triclinic space group P as 4.2CHCl3 or 4.3THF when either diethyl ether or n-pentane was allowed to diffuse into solutions of 4 in chloroform or tetrahydrofuran. The oxidation states of each manganese ion in 4.2CHCl3 or 4.3THF were assigned on the basis of detailed symmetry, bond length, and charge considerations, as well as by the Jahn-Teller axial elongation observed for the manganese(III) ions, and were further supported by cyclic voltammetry. The analysis of the SQUID magnetic susceptibility data for complex 4.2CHCl3 showed that the intramolecular magnetic coupling of the manganese(II,III) ions is dominated by ferromagnetic exchange interactions. This results in an S = 27/2 ground-state multiplet at low magnetic field. At fields higher than 0.68 T, the energetically lowest state is given by the mS = 31/2 component of the S = 31/2 multiplet due to the Zeeman effect. The ligand-field-splitting parameters were determined by anisotropy SQUID measurements on single crystalline samples along the crystallographic x, y, and z axes (D = -0.055 K, E = 6.6 mK) and by high-frequency electron spin resonance measurements on a polycrystalline powder of 4.2CHCl3 (D = -0.068 K, E = 9.7 mK). The resulting barrier height for magnetization reversal amounts to U approximately 10 K. Finally, 2DEG Hall magnetization measurements revealed that 4.2CHCl3 shows single-molecule magnet behavior up to the blocking temperature of about 0.6 K with closely spaced steps in the hysteresis because of the quantum tunneling of the magnetization.
Inorganic Chemistry 04/2007; 46(5):1586-92. · 4.60 Impact Factor
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Angewandte Chemie International Edition 02/2007; 46(19):3579-83. · 13.45 Impact Factor
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ABSTRACT: The tetranuclear complex [Fe(III)2(L')(OH)(CH3O)]2, 1, has been synthesised from the reaction of either ferrous [in excess as 4:1 or stoichiometric 2:1 iron(II) : H4L] or ferric ions [4:1 iron(III) : H4L] with the large macrocycle, H4L, using aerobic conditions in methanol in the presence of triethylamine. The structure of 1 was determined by single-crystal X-ray diffraction. These reaction conditions lead to the modification of the original macrocycle through the incorporation of a methylene group between two amine groups to give an imidazolidine ring in (L')4-. The controlled addition of formaldehyde into the reaction system results in a significantly improved yield of 1, suggesting that it is involved in the reaction mechanism. The (L')4- macrocycle binds to two, well-separated, iron(III) centres [Fe(1)...Fe(1a) > 8 A]. Each iron(III) centre is further linked via hydroxy and methoxy bridges to equivalent iron(iii) centres contained in a second macrocycle. Overall this gives a structure containing two {Fe(OH)(CH(3)O)Fe} dimers [Fe(1)...Fe(2)ca. 3.2 A] sandwiched by two (L')4- macrocycles. The complex was further characterised by SQUID magnetic measurements and can be interpreted in terms of two isolated antiferromagnetically coupled Fe(III) dimers (J=-23.75 K).
Dalton Transactions 03/2005; · 3.84 Impact Factor
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Christian Zimmermann,
Christopher E Anson,
Amanda L Eckermann,
Markus Wunder,
Gerda Fischer,
Ilka Keilhauer,
Erik Herrling, Bernd Pilawa,
Oliver Hampe,
Florian Weigend,
Stefanie Dehnen
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ABSTRACT: By reacting 1-aminoethylammonium (H2NCH2CH2NH3+ = enH+) salts of [Sn2E6]4- anions (E = S, Se), [enH]4[Sn2S6] (1) and [enH]4[Sn2Se6] x en (2), with FeCl2/LiCp, three novel (partly) oxidized, Cp* ligated iron chalcogenide clusters were synthesized. Two of them, [(CpFe)3(mu3-S)2] (3) and [(Cp*Fe)3(mu3-Se)2] (4), contain formally 47 valence electrons. [(Cp*Fe)3(SnCl3)(mu3-Se)4] x DME (5) represents the first known mixed metal Fe/Sn/Se heterocubane type cluster. Compounds 3-5 were structurally characterized by single-crystal X-ray diffraction, and the odd valence electron number of the [Fe3E2] clusters (E = S, Se) was confirmed by density functional (DFT) investigations, mass spectrometry, cyclic voltammetry and a susceptibility measurement of 3.
Inorganic Chemistry 08/2004; 43(15):4595-603. · 4.60 Impact Factor
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ABSTRACT: The Ga(84)R(20)(4-) [R = N(SiMe(3))(2)] species, which represents the largest metalloid cluster entity structurally characterized so far, has been electronically and topologically modified: Via changing the redox potential of the reaction solution, crystals different from those containing the Ga(84)R(20)(4-) anion can be isolated, featuring similar Ga(84)R(20)(3-) entities. An accurate crystal structure analysis via synchrotron radiation is presented, which might be the first step toward an understanding of the metallic conductivity and superconductivity of the Ga(84)R(20)(4-) cluster compound, physical properties which are singular in the field of metalloid clusters so far.
Inorganic Chemistry 01/2004; 42(24):7731-3. · 4.60 Impact Factor
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ABSTRACT: The magnetic properties of [Cu4(ndpa)2(H2O)6Cl2]2H2O are studied by static and dynamic magnetic susceptibility measurements. The static susceptibility measurements between 2 and 300 K reveal ferromagnetically coupled Cu(II) dimers (J/kB = +24.0 ± 0.5 K). Two further exchange constants J'/kB = −0.40 ± 0.02 K and J''/kB = 2.2 ± 0.2 K are determined by zero-field ac-susceptibility measurements in the temperature range between 12 and 0.4 K. The exchange couplings are assigned by means of electron spin resonance measurements which show that Cu4: Cl realizes a ferromagnetic alternating spin-1/2 Heisenberg chain with an antiferromagnetic interchain coupling.
Journal of Physics Condensed Matter 06/2003; 15(25):4477. · 2.55 Impact Factor
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ABSTRACT: We derive the 63Cu and 65Cu nuclear spin lattice relaxation for the Cu(5) site of oriented powder prepared from the single-crystalline heavy-fermion compounds CeCu6 and CeCu5Au. The quantitative description is based on single-crystal analysis of the anisotropic magnetic susceptibility, anisotropic transferred hyperfine interaction, and magnetically induced electric quadrupolar interaction. The temperature dependence of the correlation time of the 4f electron contribution is derived. An earlier discrepancy with neutron scattering results is removed.
Phys. Rev. B. 75(2).
