Flux trapping in the 9.3 GHz modulated microwave absorption spectra observed near 4 K from ceramic and powdered ceramic specimens of two separately prepared YBa2Cu3O7-δ samples has been used to separate the intergranular and intragranular contributions to the spectra. In the denser, glassy sample, a broad absorption with a peak near 400 Oe for forward sweeps was observed with appreciable intensity after the maximum flux was trapped. This spectrum is attributed to intergranular junctions, since its relative intensity was reduced on powdering and suspending in wax. In the less dense, more uniform sample, the latter spectrum was appreciably weaker in both ceramic and powder. Both types of junction appear to contribute to the narrow low-field absorption which was observed after zero field cooling in all the samples.

The effect of heating YBa2Cu3Ox in vacuum to 600 °C has been studied using photoelectron spectroscopy and diamagnetic susceptibility measurements. Evidence of two chemically distinct copper and barium species is found in single phase samples at room temperature cleaned by gentle heating at 450 °C. Such annealing also increases the volume diamagnetic susceptibility of the samples which suggests that the preferred stoichiometry of growth does not lead to an optimum superconducting phase. Samples cleaned by vacuum scraping or ion bombardment reveal more amorphous XPS structure and are less indicative of bulk properties.

Modulated microwave absorption measurements at 9.3 GHz were made on the low field absorption observed in the superconducting phase of Bi–Sr–Ca–Cu–O. The line intensity observed with a low modulation amplitude of 50 mOe showed a maximum between 70 K and 80 K and dropped to zero near 95 K. With a modulation amplitude of 10 Oe, an additional broad line absorption was observed above 88 K, peaking in intensity near 95 K, and disappearing above 100 K. Hysteresis, associated with flux trapping, occurred when the maximum field Hmax in a sweep cycle exceeded a critical value H*(T), which varied from about 7 Oe at 59 K to 1 Oe at 82 K. For Hmax > H*, the hysteresis splitting at first varied linearly with (Hmax – H*), later saturating at a value δHmax(T). Above 70 K, the relationship δHmax = b(T0 – T) was obeyed with T0 = 92.3 K and b· = −0.3 Oe/K for H perpendicular and b· = −0.23 Oe/K for H parallel to the c-axis.

The original motivation for the work outlined in this paper started with an attempt to find a method for measuring the anisotropy energy as well as the interplane antiferromagnetic (AF) exchange in the common layered structures of n-ethylammonium CuCU (nEA) and n-ethanediammonium CuCU (nDA). Most of these order ferromagnetically within the plane of CuCU's but the weak ferromagnetic (F) exchange between planes yields a 3D AF compound below the ordering temperature. In F resonance the strong exchange between ions is not explicit in the free energy or Hamiltorian since in the ordered F state all spins are aligned. That is, the exchange energy has already been used to provide the magnetization vector M. AF resonance, on the other hand, is typically treated as a two sublattice system where all the spins pointing in one direction are considered to be one sublattice and all those in the other direc-* tion are from the other sublattice. In this case the strong exchange in a standard 3D AF is still the exchange between neighboring spins and, therefore, becomes the exchange between sublattices and as such becomes part of the explicit free energy of the system. The fact that all the spins on one sublat-

Electron magnetic-resonance (EMR) spectra observed at liquid-helium temperatures in the one-dimensional Ising ferromagnet [(CH3)(3)NH]FeCl3. 2H(2)O result from transitions within the first excited set of cluster states. Improved fits of the EMR data in the range 10-35 GHz are presented both with and without the inclusion of the magnetic dipolar interaction within a ferrous chain. In the absence of spin canting, an expression independent of the chain length is derived for the matrix elements of the dipolar interaction. Justification for the omission of spin canting is obtained from the rotational behavior of the 17-GHz spectrum, which supports a canting angle of less than 10 degrees.

Several structural phases of gallium can be nucleated upon cooling of mixtures of liquid gallium and an excess of particulate material. One such structural phase, which we label the theta phase, was observed in gallium and fullerene mixtures and is efficiently nucleated only by particulate material of small particle size such as soot or the separation products of soot. The -phase is possibly a recently discovered phase of gallium.

The magnetic susceptibilities of the two spin-1/2 Heisenberg antiferromagnetic chain systems, 6-methyl-2-aminopyridinium trichlorocuprate(II) [(6MAP)CuCl3] and 3-methyl-2-aminopyridinium trichlorocuprate(II) [(3MAP)Cu%l(3)], have been reinvestigated. Their behavior cannot be described by a simple uniform Heisenberg antiferromagnetic chain model at low temperature, but rather by either a spin-Peierls model with a paramagnetic impurity contribution or a broken-chain model. The spin-Peierls model assumes a uniform antiferromagnetic chain above the transition temperature and a weakly dimerized antiferromagnetic chain below that temperature and yields uniform-chain exchange constants J/k of -54.5 and -59 K for (6MAP)CuCl3 and (3MAP)CuCl3, respectively, with the alternating exchange ratio 0.98<alpha<1 for both. The possible spin-Peierls transition temperatures are about 2 K. It is also possible to explain the data by a broken-chain model which gives exchanges of -50.5 and -55.6 K for (6MAP)CuCl3 and (3MAP)CuCl3, respectively. In this model the average chain lengths of two compounds are estimated.

The results of the complex dielectric permittivity measurements and the spin-lattice relaxation times of the deuterated glass D-RADA x = 0.46, by the dielectric and EPR techniques are reported. The transition from paraelectric to antiferroelectric phase is detected at TN = 162 K. Below 90 K the dispersion of the complex dielectric permittivity was detected. The shape of the temperature dependence of the imaginary part of the dielectric permittivity was analyzed. This analysis shows the existence of two relaxation phases forming among the antiferroelectric domains, described by Arrhenius equation, and the glass state appears after the antiferroelectric ordering has been destroyed. The dielectric results are confirmed by the spin-lattice relaxation times data.

Low-temperature magnetic-resonance spectra at 9.2-9.3 GHz in single crystals of the one-dimensional Ising ferromagnet FeTAC, [(CH3)3NH] FeCl3.2H2O, were strongly anisotropic with minima in the field occurring for H parallel to the easy axis. A ''strong'' signal in this orientation with a g value of 8.8 at 5.5 K (after correction for internal demagnetization and exchange fields) is identified with transitions between neighboring spin-cluster resonances. Possible origins of broad and weak lines, with maximum corrected g values of 13 and 3.7 are discussed. Spectra from samples of different shape are consistent with sample-dependent demagnetization fields.

The differential magnetic susceptibility of [(${\mathrm{CH}}_{3}$${)}_{3}$NH]${\mathrm{FeCl}}_{3}$\ensuremath{\cdot}${2\mathrm{H}}_{2}$O has been measured as a function of temperature in the range 4.2 KT20 K in fields of 0, 500, 1000, and 1500 Oe. To interpret the data, a simple model for a fermion gas of noninteracting clusters of various sizes is presented. The analysis suggests that single-spin reversals make only a small contribution to the susceptibility and that to obtain even qualitative agreement with data the effects of large spin clusters and interaction between spin clusters must be included.

The magnetic properties and critical behavior of the quasi-two-dimensional ferromagnets [C6H5(CH2)n(NH3]2CuBr4, with n = 1, 2, and 3, have been studied. These compounds are typical of layered magnets in that they assume distorted layer perovskite structures in which copper(II) bromide layers are sheathed by the bulk organic cations. Magnetization and susceptibility measurements show strong ferromagnetic intralayer exchange of the order of 20-25 K with weak interlayer exchange coupling of less than 1 K. The magnetic anisotropies are explored through EPR-linewidth analysis. The critical exponent gamma and transition temperatures T(c) were determined by the measurements of ac initial susceptibility and isothermal magnetization. By employing a static scaling law to analyze the data of isothermal magnetizations near T(c), it was found that in a certain low-field and low-temperature region the powder magnetizations are suppressed so that the scaling hypothesis no longer holds. It is shown from the scaling analysis that the powder samples of these two-dimensional (2D) layer ferromagnets cannot be classified as simple ferromagnets whose critical behavior is described by the usual 2D critical theories.

The reorientation of sublattice magnetizations from an antiferromagnetic to a spin-flop phase has been studied in the new Heisenberg quasi-two-dimensional antiferromagnet [C6H5(CH2)NH3]2CuBr4. Evidence is offered for the existence of an intermediate phase, brought about by competition between separate easy axes for antiferromagnetic (interlayer) and ferromagnetic (intralayer) ordering. Experimentally determined magnetic phase boundaries are compared with predictions of mean-field theory.

The mixed crystal ${\mathrm{Rb}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$(${\mathrm{NH}}_{4}$${)}_{\mathit{x}}$${\mathrm{H}}_{2}$${\mathrm{AsO}}_{4}$ (RADA) has been investigated for several values of (x=0,0.12,0.15, and 0.20) by measuring the complex dielectric permittivity along the a tetragonal axis in the temperature range from 3 to 300 K and frequency range from 1 Hz to 30 kHz. We find coexistence of ferroelectric and proton-glass order in RADA for x=0.12 and probably at x=0.15. The long-range ferroelectric order is not destroyed by the onset of proton-glass ordering. This behavior is similar to that of other proton-glass systems and of the magnetic Ising glass systems reported by Wong et al. in ${\mathrm{Fe}}_{0.55}$${\mathrm{Mg}}_{0.45}$${\mathrm{Cl}}_{2}$ and by Yoshizawa et al. in ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Mn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{TiO}}_{3}$. The partial phase diagram for ${\mathrm{Rb}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$(${\mathrm{NH}}_{4}$${)}_{\mathit{x}}$${\mathrm{H}}_{2}$${\mathrm{AsO}}_{4}$ including the coexisting proton-glass and ferroelectric phases is presented.

Dielectric permittivity measurements of ${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{a}}^{\ensuremath{'}}$ and ${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{a}}^{\mathrm{\ensuremath{''}}}$ in a ${\mathrm{K}}_{0.60}$(${\mathrm{NH}}_{4}$${)}_{0.40}$${\mathrm{H}}_{2}$${\mathrm{AsO}}_{4}$ mixed crystal have been made in the temperature and frequency ranges 3--300 K and 1 Hz--30 kHz. We find proton-glass behavior in this material similar to that observed in the ${\mathrm{Rb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$(${\mathrm{NH}}_{4}$${)}_{\mathrm{x}}$${\mathrm{H}}_{2}$${\mathrm{AsO}}_{4}$ and ${\mathrm{Rb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$(${\mathrm{NH}}_{4}$${)}_{\mathrm{x}}$${\mathrm{H}}_{2}$${\mathrm{PO}}_{4}$ systems. Below ${\mathrm{T}}_{\mathrm{g}}$ the dielectric dispersion characteristics of the freezing of the polarization are well described phenomenologically by the Vogel-Fulcher law. The best fit gives the Vogel-Fulcher temperature ${\mathrm{T}}_{0}$=5.4 K, the attempt frequency ${\ensuremath{\nu}}_{0}$=2.5\ifmmode\times\else\texttimes\fi{}${10}^{13}$ Hz, and the activation energy ${\mathrm{E}}_{\mathrm{c}}$/k=409 K.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructure and magnetic moment of pyrrolidinium copper trichloride, a linear ferromagnetDiane M. Nilsen, R. D. Larsen, Kenneth Emerson, Gerald V. Rubenacker, Zhou Ping, and John E. DrumhellerCite this: Inorg. Chem. 1990, 29, 16, 2887–2888Publication Date (Print):August 1, 1990Publication History Published online1 May 2002Published inissue 1 August 1990https://pubs.acs.org/doi/10.1021/ic00341a006https://doi.org/10.1021/ic00341a006research-articleACS PublicationsRequest reuse permissionsArticle Views142Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts