Angular dependent planar metamagnetism in the hexagonal compounds TbPtIn and TmAgGe

Detailed magnetization measurements, M(T,H,theta), were performed on single crystals of TbPtIn and TmAgGe (both members of the hexagonal Fe_2P/ZrNiAl structure type), for the magnetic field H applied perpendicular to the crystallographic c axis. These data allowed us to identify, for each compound, the easy-axes for the magnetization, which coincided with high symmetry directions ([120] for TbPtIn and [110] for TmAgGe). For fixed orientations of the field along each of the two six-fold symmetry axes, a number of magnetically ordered phases is being revealed by M(H,T) measurements below T_N. Moreover, T ~ 2 K, M(H)|_theta measurements for both compounds (with H applied parallel to the basal plane), as well as T = 20 K data for TbPtIn, reveal five metamagnetic transitions with simple angular dependencies: H_{ci,j} ~ 1/cos(theta +/- phi), where phi = 0^0 or 60^0. The high field magnetization state varies with theta like 2/3*mu_{sat}(R^{3+})*cos(theta), and corresponds to a crystal field limited saturated paramagnetic, CL-SPM, state. Analysis of these data allowed us to model the angular dependence of the locally saturated magnetizations M_{sat} and critical fields H_c with a three coplanar Ising-like model, in which the magnetic moments are assumed to be parallel to three adjacent easy axes. Furthermore, net distributions of moments were inferred based on the measured data and the proposed model

Charmed Strange Pentaquarks in the Large NcN_c Limit

The properties of pentaquarks containing a heavy anti-quark and strange quarks are studied in the bound state picture. In the flavor SU(3) limit, there are many pentaquark states with the same binding energy. When the SU(3) symmetry breaking effects are included, however, three states become particularly stable due to a ``Gell-Mann--Okubo mechanism''. They are the $\bar Qsuud$ and $\bar Qsudd$ states discussed by Lipkin, and a a previously unstudied $\bar Qssud$ state. These states will have $J^P={1\over2}^+$ and their masses are estimated. These states, if exist, may be seen in experiments in the near future.Comment: 12 pages in REVTeX, no figure

Baryons with Two Heavy Quarks as Solitons

Using the chiral soliton model and heavy quark symmetry we study baryons containing two heavy quarks. If there exists a stable (under strong interactions) meson consisting of two heavy quarks and two light ones, then we find that there always exists a state of this meson bound to a chiral soliton and to a chiral anti-soliton, corresponding to a two heavy quark baryon and a baryon containing two heavy anti-quarks and five light quarks, or a ``heptaquark".Comment: 7 pages and 2 postscript figures appended, LaTex, UCI-TR 94-3

Phenomenology of the Pentaquark Antidecuplet

We consider the mass splittings and strong decays of members of the lowest-lying pentaquark multiplet, which we take to be a parity-odd antidecuplet. We derive useful decompositions of the quark model wave functions that allow for easy computation of color-flavor-spin matrix elements. We compute mass splittings within the antidecuplet including spin-color and spin-isospin interactions between constituents and point out the importance of hidden strangeness in rendering the nucleon-like states heavier than the S=1 state. Using recent experimental data on a possible S=1 pentaquark state, we make decay predictions for other members of the antidecuplet.Comment: 12 pages LaTeX, 1 eps figur

From Tetraquark to Hexaquark: A Systematic Study of Heavy Exotics in the Large NcN_c Limit

A systematic study of multiquark exotics with one or $N_c-1$ heavy quarks in the large $N_c$ limit is presented. By binding a chiral soliton to a heavy meson, either a normal $N_c$-quark baryon or an exotic $(N_c+2)$-quark baryon is obtained. By replacing the heavy quark with $N_c-1$ heavy antiquarks, exotic $(2N_c-2)$-quark and $2N_c$-quark mesons are obtained. When $N_c = 3$, they are just the normal triquark baryon $Qqq$, the exotic pentaquark baryon $Q\bar q\bar q\bar q\bar q$, tetraquark di-meson $\bar Q \bar Q qq$ and the hexaquark di-baryon $\bar Q \bar Q \bar q \bar q\ bar q \bar q$ respectively. Their stabilities and decays are also discussed. In particular, it is shown that the ``heavy to heavy'' semileptonic decays are described by the Isgur--Wise form factors of the normal baryons.Comment: 14 pages in REVTeX, no Figure

Search for Flavoured Multiquarks in a Simple Bag Model

We use a bag model to study flavoured mesonic $(Qq\bar q\bar q)$ and baryonic $({\overline Q}qqqq)$ states, where one heavy quark $Q$ is associated with light quarks or antiquarks, and search for possible stable multiquarks. No bound state is found. However some states lie not too high above their dissociation threshold, suggesting the possibility of resonances, or perhaps bound states in improved models.Comment: REVTEX, VERSION 3.

Prospects for Pentaquark Production at Meson Factories

Following Rosner [hep-ph/0312269], we consider B-decay production channels for the exotic I=0 and $I=3/2$ pentaquarks that have been recently reported. We also discuss new search channels for isovector pentaquarks, such as the $\Theta^{*++} (\bar s duuu)$, that are generically present in chiral soliton models but were not observed in recent experiments. Futhermore, we argue that weak decays of charmed baryons, such as the $\Lambda_c^+$ and $\Xi_c^0$, provide another clean way of detecting exotic baryons made of light quarks only. We also discuss discovery channels for charmed pentaquarks, such as the isosinglet $\Theta_c^0 (\bar c udud)$, in weak decays of bottom mesons and baryons. Finally, we discuss prospects for inclusive production of pentaquarks in $e^+ e^-$ collisions, with associated production of particles carrying the opposite baryon number.Comment: 15 pages, LaTeX; v2,v3: minor corrections, references added; v4: minor modifications, the version published in Physics Letters

Metallic ferromagnetism without exchange splitting

In the band theory of ferromagnetism there is a relative shift in the position of majority and minority spin bands due to the self-consistent field due to opposite spin electrons. In the simplest realization, the Stoner model, the majority and minority spin bands are rigidly shifted with respect to each other. Here we consider models at the opposite extreme, where there is no overall shift of the energy bands. Instead, upon spin polarization one of the bands broadens relative to the other. Ferromagnetism is driven by the resulting gain in kinetic energy. A signature of this class of mechanisms is that a transfer of spectral weight in optical absorption from high to low frequencies occurs upon spin polarization. We show that such models arise from generalized tight binding models that include off-diagonal matrix elements of the Coulomb interaction. For certain parameter ranges it is also found that reentrant ferromagnetism occurs. We examine properties of these models at zero and finite temperatures, and discuss their possible relevance to real materials

Rare earth contributions to the X-ray magnetic circular dichroism at the Co K edge in rare earth-cobalt compounds investigated by multiple-scattering calculations

The X-ray magnetic circular dichroism (XMCD) has been measured at the Co K edge in Co-hcp and R-Co compounds (R=La, Tb, Dy). The structure of the experimental XMCD spectra in the near-edge region has been observed to be highly sensitive to the magnetic environment of the absorbing site. Calculations of the XMCD have been carried out at the Co K edge in Co metal, LaCo$_5$ and TbCo$_5$ within the multiple-scattering framework including the spin-orbit coupling. In the three systems, the XMCD spectra in the near-edge region are well reproduced. The possibility to separate and quantitatively estimate the local effects from those due to the neighboring atoms in the XMCD cross section makes possible a more physical understanding of the spectra. The present results emphasize the major role played by the $d$ states of the Tb ions in the XMCD spectrum at the Co K edge in the TbCo$_5$ compound.Comment: 34 pages, revtex, 10 eps figures included with epsf, after referee revie

Combining two-directional synthesis and tandem reactions. Part 21: Exploitation of a dimeric macrocycle for chain terminus differentiation and synthesis of an sp3-rich library

The application of a tandem condensation/cyclisation/[3+2]-cycloaddition/elimination reaction gives an sp3-rich tricyclic pyrazoline scaffold with two ethyl esters in a single step from a simple linear starting material. The successive hydrolysis and cyclisation (with Boc anhydride) of these 3-dimensional architectures, generates unprecedented 16-membered macrocyclic bisanhydrides (characterised by XRD). Selective amidations could then be achieved by ring opening with a primary amine followed by HATU-promoted amide coupling to yield an sp3-rich natural product-like library