Purification and Magnetic Interrogation of Hybrid Au-Fe(3) O(4) and FePt-Fe(3) O(4) Nanoparticles

Purifying heterodimers: Differential magnetic catch and release separation is used to purify two important hybrid nanocrystal systems, Au-Fe(3) O(4) and FePt-Fe(3) O(4) . The purified samples have substantially different magnetic properties compared to the as-synthesized materials: the magnetization values are more accurate and magnetic polydispersity is identified in morphologically similar hybrid nanoparticles.     

Zeeman effect in CaF(2Pi(3/2))

The Zeeman effect in the excited A 2Pi(3/2) state of CaF is measured and analyzed over a wide range of magnetic fields. It is found that the splitting of the Zeeman levels is largely determined by the coupling between different rotational states and there are no low-field seeking states in the J=3/2 manifold of Zeeman levels at high magnetic fields. A model of the Zeeman spectrum based on the ligand-field theory of CaF is shown to be accurate in the interval of magnetic fields 0-5 Tesla. This demonstrates that the magnetic moment of the CaF(A 2Pi(3/2)) molecule is effectively determined by the spin angular momentum of a single electron and the orbital motion of the valence electron around the Ca2+ core. An analysis of the Zeeman spectrum as a function of the molecular rotational constant indicates that 2Pi(3/2) molecules should have significant rotational constants (at least as large as twice the rotational constant of CaF) to be amenable to magnetic trapping in high fields.     

Bifunctional Mixed-Lanthanide Cyano-Bridged Coordination Polymers Ln(0.5)Ln'(0.5)(H(2)O)(5)[W(CN)(8)] (Ln/Ln' = Eu(3+)/Tb(3+), Eu(3+)/Gd(3+), Tb(3+)/Sm(3+))

A new family of mixed-lanthanide cyano-bridged coordination polymers Ln(0.5)Ln'(0.5)(H(2)O)(5)[W(CN)(8)] (where Ln/Ln' = Eu(3+)/Tb(3+), Eu(3+)/Gd(3+), and Tb(3+)/Sm(3+)) containing two lanthanide and one transition metal ions were obtained and characterized by X-ray diffraction, photoluminescence spectroscopy, magnetic analyses, and theoretical computation. These compounds are isotypical and crystallize in the tetragonal system P4/nmm forming two-dimensional grid-like networks. They present a magnetic ordering at low temperature and display the red Eu(3+) ((5)D(0) → (7)F(0-4)) and green Tb(3+) ((5)D(4) → (7)F(6-2)) characteristic photoluminescence. The Tb(0.5)Eu(0.5)(H(2)O)(5)[W(CN)(8)] compound presents therefore green and red emission and shows Tb(3+)-to-Eu(3+) energy transfer.     

Theoretical investigation of the spin exchange interactions and magnetic properties of the homometallic ludwigite Fe(3)O(2)BO(3)

The homometallic ludwigite Fe(3)O(2)BO(3) has a complex structure made up of corner- and edge-sharing FeO(6) octahedra and exhibits a number of apparently puzzling magnetic properties. The reasons for these properties were probed by examining the trends in the spin exchange interactions of Fe(3)O(2)BO(3). To analyze the relative strengths of spin exchange interactions in such a complex magnetic solid, we first generalized the method of spin dimer analysis and then employed the resulting formulation to investigate how the magnetic properties of Fe(3)O(2)BO(3) are related to its reported crystal structures. The spin-orbital interaction energies calculated for various spin dimers of Fe(3)O(2)BO(3) provide estimates for the relative strengths of the associated spin exchange interactions, which in turn account for the observed magnetic properties of Fe(3)O(2)BO(3).     

Multiple areas of magnetic bistability in the topological ferrimagnet [Co3(NC5H3(CO2)2-2,5)2(mu3-OH)2(OH2)2

Hydrothermal reaction of CoCl2 with the potassium salt of pyridine-2,3-dicarboxylic acid and excess base yields [Co3(NC5H3(CO2)2-2,5)2(mu3-OH)2(OH2)2], which has a three-dimensional structure based on hydroxide-bridged triangular chains. The magnetic behavior of this compound shows the presence of three distinct regions of magnetic bistability.     

Spin dimer analysis of the spin exchange interactions in paramelaconite Cu(4)O(3) and its analogue Ag(2)Cu(2)O(3) and the spin ordering of the Cu(2)O(3) spin lattice leading to their magnetic phase transitions

The magnetic structures of the Cu(2)O(3) spin lattices present in Cu(4)O(3) and Ag(2)Cu(2)O(3) were analyzed by studying their spin exchange interactions on the basis of spin dimer analysis. Calculations of spin exchange parameters were calibrated by studying LiCuVO(4) whose intrachain and interchain antiferromagnetic spin exchange parameters are known experimentally. The magnetic phase transition of Cu(4)O(3) at 42.3 K doubles the unit cell along each crystallographic direction. The spin arrangements of the Cu(2)O(3) lattice consistent with this experimental observation are different from conventional antiferromagnetic ordering. Our analysis indicates that spin fluctuation should occur in Cu(4)O(3), low-dimensional magnetism should be more important than magnetic frustration in Cu(4)O(3), and Ag(2)Cu(2)O(3) and Cu(4)O(3) should have similar structural and magnetic properties.     

The structure and magnetic properties of μ3-oxotriiron(III) complex [Fe3O(OBz)6(CH3OH)3](NO3)(CH3OH)2

A new μ₃-O triiron(III) complex [Fe₃O(OBz)₆(CH₃OH)₃](NO₃)(CH₃OH)₂ (HOBZ = benzoic acid) has been synthesized, its structure has been determined and variable temperature magnetic susceptility has also been measured. In the molecule, three iron atoms formed an equilateral triangle with μ₃-O in center. The fitting to the magnetic susceptibility showed that an intramolecular antiferromagnetic exchange interaction occurred between iron atoms with J=-25.51 cm^?1, and a weaker intermolecular autiferromagnetic exchange interaction occurred with zJ' = ?2.30 cm^?1.     

Analysis of the uniaxial magnetic properties of high-spin d(6) ions at trigonal prism and linear two-coordinate sites: uniaxial magnetic properties of Ca(3)Co(2)O(6) and Fe[C(SiMe(3))(3)](2)

It was shown that high-spin d(6) ions at trigonal prism and linear two coordinate sites have uniaxial magnetic properties by calculating their low-lying eigenstates under the influence of crystal field and spin-orbit coupling and then determining their g-factors for the parallel and perpendicular directions. On the basis of our theoretical findings, we interpreted the uniaxial magnetic properties of Ca(3)Co(2)O(6) with high-spin Co(3+) (d(6)) ions at the trigonal prism sites and those of Fe[C(SiMe(3))(3)](2) with high-spin Fe(2+) (d(6)) ions at linear two-coordinate sites, and discussed why compounds with high-spin d(6) ions at octahedral sites cannot have uniaxial magnetic properties.     

Low temperature neutron diffraction studies in [Mn3(suc)2(ina)2]n: an homometallic molecular 3D ferrimagnet

Neutron diffraction techniques have been used to determine the low temperature crystal structure and to shed light on the magnetic behavior of the [Mn(3)(suc)(2)(ina)(2)](n) (suc = succinate and ina = isonicotinate) complex. The ferromagnetic signal observed below T(c) ≈ 5 K in this compound is due to a noncompensation of homometallic spins in the 3D framework. The Mn(II) magnetic moments obtained from neutron diffraction refinements are slightly lower than those observed for isolated Mn(II) ions; this can be due to covalent spin delocalization or geometrical magnetic fluctuations. A small discrepancy between the value of the magnetic moments of each Mn(II) site is also observed [Mn(1) 4.1(2) μ(B) and the Mn(2) 3.9(1) μ(B)]. These differences between the theoretical and observed manganese magnetic moments are not unexpected in this large spin metal complex, and qualitatively reasonable given the synergistic interaction between the metal ions through oxo-bridge. The competition among different interactions, principally those covalent through organic ligands and dipolar interaction, drive to a final 3D ferrimagnetic order.     

Pressure-induced crystal structure and spin-state transitions in magnetite (fe(3)o(4))

High pressure is an important dimension for the emergent phenomena in transition metal oxides, including high-temperature superconductivity, colossal magnetoresistance, and magnetoelectric coupling. In these multiply correlated systems, the interplay between lattice, charge, orbital, and spin is extremely susceptible to external pressure. Magnetite (Fe(3)O(4)) is one of the oldest known magnetic materials and magnetic minerals, yet its high pressure behaviors are still not clear. In particular, the crystal structure of the high-pressure phase has remained contentious. Here, we investigate the pressure-induced phase transitions in Fe(3)O(4) from first-principles density-functional theory. It is revealed that the net magnetic moment, arising from two ferrimagnetically coupled sublattices in Fe(3)O(4), shows an abrupt drop when entering into the high-pressure phase but recovers finite value when the pressure is beyond 65.1 GPa. The origin lies in the redistribution of Fe 3d orbital occupation with the change of crystal field, where successive structural transitions from ambient pressure phase Fd3?m to high pressure phase Pbcm (at 29.7 GPa) and further to Bbmm (at 65.1 GPa) are established accurately. These findings not only explain the experimental observations on the structural and magnetic properties of the highly compressed Fe(3)O(4) but also suggest the existence of highly magnetized magnetite in the Earth's lower mantle.     

A pyrazolate-supported Fe(3)(mu(3)-O) core: structural, spectroscopic, electrochemical, and magnetic study

A comparison is made between the structural, spectroscopic, electrochemical, and magnetic properties of pyrazolate versus carboxylate complexes [Fe3(mu3(mu3O)(mu-LL)6Cl3]2- containing the Fe3(mu3-O)-motif. While the Fe3(mu3-O)-cores are structurally indistinguishable in the two types of complexes, their magnetic properties deviate from the expected values as a result of a through-pyrazole contribution to the overall antiferromagnetic exchange with J1/hc = -80.1 cm(-1) and J2/hc = -72.4 cm(-1), or J1/hc = 70.6 cm(-1) and J2/hc = -80.8 cm(-1), (Hex = -J1(S1S2 + S2S3) - J2S1S3). The magnetic properties of the pyrazolate complexes are further tuned by an antisymmetric exchange interaction term.     

Synthesis and characterisation of ReOCl3(DTO)2 and ReOCl3(MBT)2 complexes

New complexes of Re(V) with dithiooxamide and 2-mercaptobenzothiazole with the general formula ReOCl₃L₂, were prepared starting from potassium perrhenate. The compounds were characterised by chemical analysis, optical spectra and magnetic susceptibilities.     

Synthesis,Structure and Characterization of Three Metal Molybdate Hydrates: Fe(H2O)2(MoO4)2·H3O,NaCo2(MoO4)2(H3O2)and Mn2(MoO4)3·2H3O

Three metal molybdate hydrates,Fe(H2O)2(MoO4)2·H3O(FeMo),NaCo2(MoO4)2(H3O2)(CoMo)and Mn2(MoO4)3·2H3O(MnMo),were synthesized by the mixed-solvent-thermal methods and characterized by singlecrystal X-ray...     

Synthesis, crystal structure, and magnetic studies of oxo-centered trinuclear chromium(III) complexes: [Cr(3)(mu(3)-O)(mu(2)-PhCOO)(6)(H(2)O)(3)]NO(3). 4H(2)O.2CH(3)OH, a case of spin-frustrated system, and [Cr(3)(mu(3)-O)- (mu(2)-PhCOO)(2)(mu(2)-OCH(2)CH(3))(2)(bpy)(2)(NCS )(3)], a new type of [Cr(3)O] core

The synthesis, crystal structure, and magnetic properties of two trinuclear oxo-centered carboxylate complexes are reported and discussed: [Cr3(mu3-O)(mu2-PhCOO)6(H2O)3]NO3.4H2O.2CH3OH (1) and [Cr3(mu3-O)(mu2-PhCOO)2(mu2-OCH2CH3)2(bpy)2(NCS)3] (2). For both complexes the crystal system is monoclinic, with space group C2/c for 1 and P1/n for 2. The structure of complex 1 consists of discrete trinuclear cations, associated NO3- anions, and lattice methanol and water molecules. The structure of complex 2 is built only by neutral discrete trinuclear entities. The most important feature of 2 is the unusual skeleton of the [Cr3O] core due to the lack of peripheral bridging ligands along one side of the triangular core, which is unique among the structurally characterized (mu3-oxo)trichromium(III) complexes. Magnetic measurements were performed in the 2-300 K temperature range. For complex 1, in the high-temperature region (T > 8 K), experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J12S1S2 - 2J13S1S3 - 2J23S2S3 (J12 = J13 = J23) with Jij = -10.1 cm(-1), g = 1.97, and TIP = 550 x 10(-6) emu mol(-1). The antisymmetric exchange interaction plays an important role in the magnetic behavior of the system, so in order to fit the experimental magnetic data at low temperature, a new magnetic model was used where this kind of interaction was also considered. The resulting fitting parameters are the following: Gzz = 0.25 cm(-1), delta = 2.5 cm(-1), and TIP = 550 x 10(-6) emu mol(-1). For complex 2, the experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J1(S1S2 + S1S3) - 2J2(S2S3) with J1 = -7.44 cm(-1), J2 = -51.98 cm(-1), and g = 1.99. The magnetization data allows us to deduce the ground term of S = 1/2, characteristic of equilateral triangular chromium(III) for complex 1 and S = 3/2 for complex 2, which is confirmed by EPR measurements.     

Syntheses and characterization of μ-Bis{N-(oxopropyl)-glycinamidato}-dicopper(II) and μ-Bis{n-(oxopropyl)-DL-alaninamidato}-dicopper(II)

Two new complexes, [Cu(OP-gld)]₂ and [Cu(OP-alad)]₂ (shown in Fig. 2) with a subnormal magnetic moment have been synthesized and characterized by means of analyses, magnetic susceptibility measurements, IR-, and electronic spectra, and conductivity measurement.     

Magnetische Messungen in den Mischphasen Fe13(Ge,Si)3, Fe3(Ge,Si), (Fe,Co)3Ge0,6Si0,4 und (Fe,Co)3Ge0,2Si0,8

The magnetic susceptibilities of germanides and silicides of the above composition have been measured in the ferromagnetic and paramagnetic region within the range between 80 K and 1270 K.

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Spin-glass behaviour in the coordination polymer [Co(C3H3N2)2]n

The magnetic behaviour of the coordination polymer [Co(C(3)H(3)N(2))(2)](n) has been investigated by magnetization and specific heat measurements. Low-field magnetic susceptibility shows the presence of two maxima at approximately 8 and 4 K (T(f)), which reflect short-range low-dimensional antiferromagnetic behaviour and the existence of a spin-glass-like state, respectively. The latter state was observed by magnetic irreversibility in both the zero-field cooled and field-cooled data, and was also confirmed by specific heat measurements. The magnetic specific heat (C(mag)) shows a lack of any long-range ordered peaks. Instead, a broad maximum near T(f) was observed in the C(mag)(T)/T-curve. Below T(f), the C(mag)(T) data follow the relation: C(mag)(T)/T = gamma + AT. We suggest that the competition of the antiferromagnetic (AF) intra-chain and the ferromagnetic (F) inter-chain interactions in a low-dimensional arrangement of magnetic Co(2+) ions can produce the spin-glass behaviour in the sample. The susceptibility data was analyzed in terms of a spin S = 3/2 Heisenberg linear-chain model with a small exchange energy and is consistent with the presence of both F and AF interactions. The splitting of the crystal field energy levels of the Co(2+) ions causes a Schottky-type specific heat anomaly of around 60 K.     

A single crystal ESR study of Gd(bipy)2(NO3)3 in La(bipy)2(NO3)3

The single crystal ESR spectrum of Gd³⁺ doped into La(bipy)₂(NO₃)₃ has been recorded at 290 K for many orientations of the crystal axes with respect to the magnetic field. A good fit of the spin Hamiltonian parameters to the experimental data has been achieved with a more efficient algorithm than previously used in this context, a significant saving being the computation of the eigenvalues only. It has been shown that previously reported spin Hamiltonian parameters for the title compound are not sufficient to describe the spectra recorded for arbitrary orientations of the single crystal and that low symmetry Gd³⁺ complexes require all possible parameters to be included.     

Preparation,Characterization, and Reactions of Dinuclear Tris(2,2,2-trichloroethoxy) Iron(III), Fe(OCH2CCl3)3

The preparation, electrical conductivity, magnetic moments, infrared, reflectance, and ⁵⁷Fe Mössbauer spectra of tris(2,2,2-trichloroethoxy) iron(III) and its adducts with some oxygen and nitrogen donor ligands are reported. Cryoscopic data of the parent compound and its complex with ethylacetate suggest these compounds to be dimeric in nitrobenzene and benzene respectively. All the compounds are covalent with Fe^III having distorted octahedral arrangement which is achieved through alkoxy bridging. The magnetic moments are lesser than those required for the spin only value indicating antiferromagnetic interactions in Fe^III atoms. The Mössbauer spectra are explained in terms of two Fe^III high spin sites corresponding to trans- and cis-positions in the structure.     

Magnetic interactions in A-site-ordered perovskites LnCu3(Ge(3/4)Ga(1/4))4O12 (Ln = La, Dy)

A-site-ordered perovskites LaCu(3)(Ge(3/4)Ga(1/4))(4)O(12) and DyCu(3)(Ge(3/4)Ga(1/4))(4)O(12) were synthesized, and their magnetism was investigated. Ferromagnetic ordering of the square-planar-coordinated Cu(2+) spins was observed at 12-13 K in both compounds, and the Dy(3+) moment in DyCu(3)(Ge(3/4)Ga(1/4))(4)O(12) stayed paramagnetic below T(C). The decoupling of the magnetic behavior of Cu(2+) and Dy(3+) sublattices revealed the weak magnetic interaction between Cu(2+) and Dy(3+).