Diamagnetic Host Research Articles

Electron paramagnetic resonance study of Mn2+-ion-doped nickel bis (hydrogen maleate) hexahydrate single crystals

Mn2+-doped nickel bis (hydrogen maleate) hexahydrate single crystals have been studied by electron paramagnetic resonance (EPR) from room temperature to liquid nitrogen temperature at X-band. From the observed EPR spectrum the spin-Hamiltonian parameters have been evaluated and the Mn2+ was found to substitute for Ni2+ ions in the host lattice. The observation of unusual well resolved Mn2+ spectrum at room temperature and its broadening on lowering the temperature in Ni[C4H3O4]2·6H2O: Mn2+ single crystals have been explained in terms of the `spin-quenching concept'. The observed shift in the g-factor of the Mn2+ ion from that in diamagnetic hosts is probably due to the Ni2+ ions, which produce a local static magnetic field at the site of Mn2+ ions. The covalency percentage of the Mn–O bond has been estimated to be 9.2%.

Optically detected magnetic resonance via the magnetic circular dichroism of absorption of cerium impurities in bulk paramagnetic terbium gallium garnet

The paramagnetic resonance of dilute ions in the bulk paramagnetic host is separated from the host response by means of optically detected magnetic resonance (ODMR) using the magnetic circular dichroism (MCD) of the absorption. This result shows that it is possible in principle to extend by means of the ODMR of the absorption the regime of paramagnetic resonance detection of impurity ions to magnetic hosts, which strongly interact with the microwave field and, hence, make the impurity signals unobservable by means of conventional EPR. The observed ODMR signals are attributed to and ions by correlation with the optical bands of these species. By means of ODMR via the Faraday effect it is shown that this effect is due to transitions between Tb levels. The identification of the observed magnetic resonance structures is confirmed by calculations based on known information on and in diamagnetic hosts. The role of molecular fields is discussed.

Quantitative extraction and analysis of carriers of magnetization in sediments

We have applied an integrated procedure for quantitative magnetic mineral extraction, based on the separation method of Petersen, von Dobeneck & Vali (1986), to a range of sediment types, to examine the efficiency and representative nature of the extraction process. Carriers of magnetization have been identified by rock magnetic measurements, microscopy and X-ray diffraction. Quantification of the extraction efficiencies is achieved by before- and after-extraction rock magnetic measurements (susceptibility, anhysteretic and isothermal remanences). These magnetic measurements show that our modified extraction method extracts large proportions of the magnetization carriers in a range of sediment types (e.g. over 75 per cent for magnetite-dominated sediments). The extraction efficiency is dependent on the sample magnetic mineralogy and whether the magnetic grains occur as discrete grains or as inclusions within host grains. Susceptibility extraction efficiencies are strongly dependent on whether the susceptibility is of paramagnetic or ferrimagnetic origin. The amount of material recovered in the extract shows some inverse correlation with the density of the sediment suspension used during extraction. In terms of the mineralogies extracted, we identify a diverse and complex range of mineral assemblages. All sizes of discrete grains of magnetite are extracted (including single-domain and superparamagnetic grains, and chains of bacterial magnetite). Other commonly extracted iron and titanium oxides are haematite and ilmenite. Ferrimagnetic chromites and sulphides were also obtained from some samples. Considerable amounts of quartz and feldspar are extracted, due to the presence of magnetic inclusions within these diamagnetic host grains. In the deep-sea sediments we examined, feldspars constitute a large proportion of the extracts, but are significantly less abundant in other sediments, where quartz is dominant. A wide variety of paramagnetic minerals was identified in the extracts, including pyroxenes, amphiboles, chlorites, micas, Mg–Cr-spinels, garnets, Ti-oxides, apatites, tourmaline and zircon, many of which contain ferrimagnetic inclusions, possibly less than 0.1 μm in grain size. Dissolution of ultrafine grains of magnetite during pre-extraction carbonate dissolution, as suggested by Sun & Jackson (1994), does not occur in our samples.

ESR Investigation of Single Crystal of (Bu_4N)_2[Cu/Pd(dmit)_2

By incorporating (Bu4N)2[Cu(dmit)2] with the diamagnetic host complex (Bu4N)2[Pd (dmit)2], single crystal of (Bu4N)2[Cu/Pd(dmit)2] is obtained. Its ESR spectra of various orientations are recorded. The principal values of g and A tensors and their direction cosines are computed using a least-squares fitting procedure, and based on which the molecular orbital of unpaired electron in [Cu(dmit)2]2- is described. The essence of the two magnetically non-equivalent sites is also revealed.

Effect of molecular motion on electron spin phase memory times for copper(II) complexes in doped solids

Electron spin phase memory times,T m, as a function of temperature were measured for Cu(II) bis(diethyldithiocarbamate), Cu(Et2dtc)2; Cu(II) bis(diethyldithiophosphate), Cu(Et2dtp)2; Cu(II) bis(diphenyldithiophosphate), Cu(Ph2dtp)2; Cu(II) tetratolylporphyrin, CuTTP; vanadyl 5-(4-carboxyphenyl)-10,15,20-tritolylporphyrin, VOTTP-COOH; and Ag(II) tetratolylporphyrin, AgTTP, doped into powdered samples of closely-related diamagnetic hosts. For the three metalloporphyrins, the electron spin relaxation rate (1/T m) increased monotonically with increasing temperature. However the temperature dependence of the relaxation rate was not monotonic for the three other Cu(II) complexes. For Cu(Et2dtc)2 and Cu(Et2dtp)2 the temperature dependence of 1/T m between about 85 and 130 K is attributed to the effects of methyl rotation, with activation energies of 1.0 kcal/mole. Between 120 and 250 K the 1/T m data for Cu(Ph2dtp)2 exhibit effects that are attributed to motion of the phenyl rings.

Determination of the structural parameters of the crystalCdCl2by use of transition-metal-ion probes

The bonding distance R and the trigonal distortion of complexes M${\mathrm{Cl}}_{6}^{4\mathrm{\ensuremath{-}}}$ at 77 K formed in ${\mathrm{CdCl}}_{2}$ crystals by substitution of ${\mathrm{Ni}}^{2+}$ and ${\mathrm{V}}^{2+}$ for ${\mathrm{Cd}}^{2+}$ have been determined from existing EPR and optical-transition data. The two different ion probes yield consistent results, which also agree with x-ray data for the position, but will be shown to be more precise by nearly an order of magnitude. This accuracy estimate depends on the validity of the theoretical calculations based on a point-charge-dipole model with a covalency correction. The case of ${\mathrm{Mn}}^{2+}$-ion probe in ${\mathrm{CdCl}}_{2}$ crystals is also discussed. In view of the fact that the theory is more complex for the $^{6}$S-state ion ${\mathrm{Mn}}^{2+}$ than for F-state ions and that a complete theoretical treatment of zero-field splittings for $^{6}$S-state ions is very difficult, it is concluded that for the determination of structural parameters of diamagnetic host from EPR spectra, the S-state-ion probe is not as effective as the F-state-ion probe.

Coherent anti stokes Raman scattering and magnetooptical interband- transitions in superlattices of diluted magnetic IV–VI semiconductors

In diluted magnetic IV–VI semiconductors like PbMnTe or PbMnSe there is a strong dependence of the effective g-factors of conduction and valence band on temperature and magnetic field. This modification of the spin splittings with respect to the diamagnetic host materials is caused by an exchange interaction between the free carriers and the magnetic moments of the paramagnetic ions. In quantum wells (QW's) or superlattices (SL's) the strength of the exchange interaction depends on the penetration of the wave functions of the free carriers into the diluted magnetic component. Detailed informations on the bandstructure of PbSe/PbMnSe SL's and MQW's are achieved for different concentrations of the magnetic ions and different widths of the quantum wells by interbandabsorption and coherent Raman experiments (CARS). Particularly CARS yields very precise data on the spin splittings of carriers confined in the quantum wells. In type I' MQW's the interband transitions which are indirect in real space give complementary informations. The analysis of CARS data from various PbMnSe/PbSe QW structures yields a type I′ alignment with electrons confined in the PbMnSe layers and holes in the PbSe layers. The interband magnetooptical data support these conclusions.

Remarks on the ground state of low-spin Cobalt(II) triazene-1-oxide complexes

Single-crystal ESR studies on low-spin bis(3-phenyl-1-ethyltriazene-1-olato) cobalt(II) doped into the diamagnetic host lattice of the isomorphous nickel(II) complex have been performed. McGarvey's theory of low-spin d 7 ions and modified INDO calculations have been applied in order to account for the spin-Hamiltonian parameters obtained. On the basis of the data obtained, g x = 2.67, g y = 2.07, g z = 1.98, A x = 16 × 10 −4 cm −1, A y = 28 × 10 −4 cm −1, A z = 36 × 10 −4 cm −1, and the observed superhyperfine structure due to equatorially disposed 14N nuclei, the ¦ z 2 > 1 ground state has been proposed. This same result was obtained on the basis of modified INDO (GRINDOL) calculations.

Mössbauer study of paramagnetic relaxation effect in mixed crystals: High spin Fe3+ compounds diluted in diamagnetic hosts

The57Fe Mossbauer spectra were measured in mixed crystals with different types of chemical bonding and crystal structure, i.e., (Fe,Al)(acac)3, (Fe,Co)(acac)3, K3[(Fe,Al)(ox)3]3H2O, and NH4(Fe,Al)(SO4)212H2O. The broadening of Mossbauer linewidth with increasing Fe3+−Fe3+ distance became less enhanced in the order: (Fe,Al)(acac)3>(Fe,Co)(acac)3, or K3[(Fe,Al)(ox)3]3H2O>(Fe,Al)(acac)3>NH4(Fe,Al)(SO4)212H2O. Furthermore, it was found that the broadening of the linewidth was larger in neat tris (β-diketonato) iron(III) complexes than in (Fe,Al)(acac)3. Based on these results, the determining factors of the paramagnetic relaxation time other than Fe3+−Fe3+ distance and temperature were examined in terms of the Mossbauer linewidth as an indicator.

Langmuir-Blodgett films of pure long-chain nitroxides, their mixtures and mixtures with stearic acid studied by electron spin resonance

In this paper we report information on the spreading isotherms and the electron spin resonance (ESR) spectra of mono- and multilayer films built up with long hydrocarbon chain nitroxides (namely doxyl stearic acid and hexadecanoyl- piperidine-oxyl radicals). These ultrathin molecular assemblies were prepared from (i) single components, (ii) nitroxide binary mixtures, and (iii) a diluted solution of the paramagnetic components in a diamagnetic (stearic acid) host. The spreading isotherms allowed us to establish that the presence of a five- or six-membered ring in the hydrocarbon chain rendered the film more expanded, and this effect depended on the substituent position in the chain. The ESR spectra of undiluted nitroxides were characterized by strong spin-spin (dipole-dipole and Heisenberg spin exchange) magnetic interactions whose extent also depended on the nitroxide type and mixture. The calculation of the parameters of motion governing the ESR lineshape allowed accurate evaluation both of the degree of order and of the chain flexibility, particularly for diamagnetically diluted systems.

ChemInform Abstract: Single‐Crystal EPR Spectrum of the Phosphido‐Bridged Radical Fe2(CO)7(μ‐PPh2).

AbstractThe EPR spectrum of the 33e title compound (Ib) is measured in the diamagnetic host (Ia) at 77 K. The crystal structure of the host complex (P1, Z=2) is established by X‐ray diffractometry.

13C CP-MAS NMR of Hofmann-type Clathrates

Abstract The 13C CP-MAS NMR spectra of two Hofmann-type clathrates, diamagnetic Cd(NH3)2Ni (CN)4·2C6H6 and paramagnetic Ni (NH3)2-Ni (CN)4·2C6H6, were analyzed. The guest benzene gives a singlet spectral line in the diamagnetic host and a doublet in the paramagnetic one. The doublet is due to the paramagnetic anisotropy at the crystallographically-independent two carbon atoms in the crystal structure.

ChemInform Abstract: Semimagnetic Lead Salt Alloys

The magnetic and electronic properties of pseudobinary alloys of the lead compounds (PbTe,PbSe)with Manganese, Europium and Gadolinium are reviewed. These materials have a direct minimum gap at the L-point of the Brillouin zone. The addition of Mn, Eu, or Gd to the diamagnetic hosts causes a rather weak antiferromagnetic exchange interaction. For sufficiently high carrier concentrations (10 2 0 -102 1 cm−3) a ferromagnetic interaction occurs due to RKKY interaction. The spin-spin exchange interaction between the Bloch states and the localized 3d or 4f states is characterized by rather small exchange integrals and the limited applicability of the mean field approximation for the description of energy band parameters like g-factors. Interband transitions in PbMnTe and PbMnS lend support to a zeromagnetic field splitting (“spin-splitting”)of band states which increases linearly with Mn-content up to several meV at temperatures below 4K.

EPR of Co2+-doped NiSO4

X-band EPR measurements on ${\mathrm{Co}}^{2+}$-doped isostructural single crystals of paramagnetic host ${\mathrm{NiSO}}_{4}$\ensuremath{\cdot}${7\mathrm{H}}_{2}$O and diamagnetic host ${\mathrm{MgSO}}_{4}$\ensuremath{\cdot}${7\mathrm{H}}_{2}$O have been made at liquid-helium temperature. The principal values of the g\ensuremath{\rightarrow} $^{2}$ and A\ensuremath{\rightarrow} $^{2}$ tensors, as well as the orientations of the principal axes of the g\ensuremath{\rightarrow} $^{2}$ and A\ensuremath{\rightarrow} $^{2}$ tensors, are evaluated from the data using a rigorous least-squares-fitting program suitable for electron-nuclear spin-coupled systems. Using the g shift of ${\mathrm{Co}}^{2+}$ in the paramagnetic lattice from that in the diamagnetic lattice the value of -0.81 GHz for the average ${\mathrm{Co}}^{2+}$-${\mathrm{Ni}}^{2+}$ exchange constant in ${\mathrm{NiSO}}_{4}$\ensuremath{\cdot}${7\mathrm{H}}_{2}$O has been estimated using the molecular-field approximation.

Semimagnetic Lead Salt Alloys

AbstractThe magnetic and electronic properties of pseudobinary alloys of the lead compounds (PbTe,PbSe)with Manganese, Europium and Gadolinium are reviewed. These materials have a direct minimum gap at the L-point of the Brillouin zone. The addition of Mn, Eu, or Gd to the diamagnetic hosts causes a rather weak antiferromagnetic exchange interaction. For sufficiently high carrier concentrations (10 2 0 -102 1 cm−3) a ferromagnetic interaction occurs due to RKKY interaction. The spin-spin exchange interaction between the Bloch states and the localized 3d or 4f states is characterized by rather small exchange integrals and the limited applicability of the mean field approximation for the description of energy band parameters like g-factors. Interband transitions in PbMnTe and PbMnS lend support to a zeromagnetic field splitting (“spin-splitting”)of band states which increases linearly with Mn-content up to several meV at temperatures below 4K.

Host-lattice systematics of EPR spectra of Mn2+-doped isomorphic metal hexakisantipyrine perchlorate and EPR of Cu2+ in copper pentakisantipyrine perchlorate

X-band EPR measurements on Mn2+-doped single crystals of isomorphous metal hexakisantipyrine perchlorate (metal=Ca, Cd, Mg, Co, and Pb) have been performed. For the case of calcium and cadmium metal hosts, the measurements were made from room temperature down to liquid helium temperature, while for the remaining metal hosts the measurements were made only at room temperature. The spin Hamiltonian parameters are rigorously evaluated using a least-squares fitting computer technique, especially adapted to electron-nuclear spin coupled systems. As for the systematics of the spin Hamiltonian parameters, at room temperature the variation of the zero field splitting parameters b02 and b04 is found to be approximately linear in the host metal ion radius. In order to estimate the Cu2+–Mn2+ exchange interaction, 5%–50% of Ca2+ ions in Mn2+-doped calcium hexakisantipyrine perchlorate were substituted for by Cu2+, and the EPR spectra were recorded from room temperature down to liquid helium temperature. However, even at liquid helium temperature, the presence of the paramagnetic ion Cu2+ in this host caused no significant change of the g value for Mn2+ as compared with that in the pure diamagnetic host indicating negligible Cu2+–Mn2+ exhange constant. EPR measurements on Cu2+ in copper pentakisantipyrine perchlorate were also made at room, liquid nitrogen, and liquid helium temperatures and the principal values and direction cosines of the principal axes of the g and A tensors were estimated, using a rigorous least-squares fitting procedure.

The Chemistry of Platinum in the +3 Oxidation State

AbstractPlatinum(III) is no longer an uncommon oxidation state. Numerous binuclear platinum(III) complexes have been prepared and structurally characterized over the past eight years. These include sulfate‐bridged dimers of D4h symmetry, [Pt2(SO4)4L2]2−, L = H2O, DMSO; phosphate‐bridged complexes [Pt2(HPO4)4‐(H2O)2]2− and [Pt2(H2PO4)(HPO4)3(py)2]−; POP (H2 P2 O2−5)‐bridged ions [Pt2‐(POP)4X2]2−, X = halide; an extensive series of α‐pyridonate (C5H4NO−)‐bridged head‐to‐head and head‐to‐tail complexes, [Pt2(NH3)4 (C5H4NO)2XY]n−, X, Y = NO3, NO2, H2O, Cl, Br; n = 2, 3; and organometallic derivatives such as [Pt2(CH3)4‐(CF3CO2)2(4‐Mepy)2]. In all cases there is a Pt–Pt single bond of length 2.47–2.7 Å, pseudo‐octahedral geometry about platinum, and two or more bridging ligands. The complexes are stable in solution and some undergo quasi‐reversible two‐electron redox reactions. Mononuclear platinum(III) complexes are less well characterized structurally, but have been stabilized in diamagnetic host lattices in the solid state and by macrobicyclic cage ligands in solution following pulse radiolytic or γ‐irradiation of precursor platinum(II) complexes. The first unequivocal, crystallographically characterized mononuclear platinum(III) complex, [Pt(C6Cl5)4]−, has just been reported.

A molecular model for the structure of copper complexes on hydrous oxide surfaces: An ENDOR study of ternary Cu(II) complexes on δ-Alumina

An ENDOR study of ternary copper(II) complexes on δ-alumina is reported. From EPR results, it is concluded, that copper has a pseudo square planar coordination geometry. The presence of protons of both axially and equatorially coordinated water is indicated by proton ENDOR data, the corresponding CuO(H 2O) distances are estimated to be 2.6(1) and 2.0(1) Å, respectively. The observed nitrogen hyperfine couplings in the ternary complexes are typical for equatorially coordinated ligands. These ENDOR data together with the EPR results allow the development of a model for the molecular structure of the surface complex. The copper and nitrogen hyperfine data are interpreted in terms of an LCAOMO model. The resulting spin density distribution is similar to that found in related copper complexes in solution or diamagnetic host matrices. The nitrogen quadrupole data are discussed in the framework of the Townes-Dailey theory.

EPR ofMn2+-doped single crystals of ZnK2(SO4)2·6H2O and NiK2(SO4)2·6H2O:Mn2+-Ni2+exchange constant

$X$-band EPR measurements on ${\mathrm{Mn}}^{2+}$-doped single isostructural crystals of diagmagnetic zinc potassium sulfate hexahydrate and paramagnetic nickel potassium sulfate hexahydrate have been made at room, liquid-nitrogren, and liquid-helium temperatures. To avoid the damagnetization effects, a spherical-shaped sample was used for the paramagnetic lattice. The spin-Hamiltonian parameters were evaluated using a least-squares fitting method, simultaneously fitting all resonant line positions obtained for several orientations of the external magnetic field. Using the $g$ shift in the paramagnetic host, from that in the isostructural diamagnetic host, the ${\mathrm{Mn}}^{2+}$-${\mathrm{Ni}}^{2+}$ exchange constant has been estimated.

The ESR linewidth of dilute solid solutions

A theoretical study of the broadening of magnetic resonance lines due to the dipole interaction in dilute solid solutions of paramagnetic impurities in diamagnetic hosts is presented. The theory takes into account the exchange interaction between impurity ions. Detailed results are presented for the three cubic lattices. The theoretical results are compared with experimental data on Cr3+:MgO powders.