Spin Density

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J Schweizer - One of the best experts on this subject based on the ideXlab platform.

  • Spin Density in interacting nitronyl nitroxide radicals
    2000
    Co-Authors: Y Pontillon, E Ressouche, Francisco M Romero, J Schweizer, Andrea Caneschi, Dante Gatteschi, Roberta Sessoli, Raymond Ziessel
    Abstract:

    Since the reported synthesis [1] of stable 2-phenyl-4,4,5,5-tetramethylimidazoline-1oxyl-3-oxide, NitPh, considerable effort has been spent in the physical characterization of nitronyl nitroxide compounds. Their general formula is presented in Figure 1A. These compounds carry a delocalized, S = 1/2, unpaired electron. Among them, some derivatives were found to be paramagnetic at low temperature (NitPh, [1]), others were found to exhibit an antiferromagnetic or a ferromagnetic behavior [2–7]. This magnetic behavior is very sensitive to the chemical structure of the Spin carrier and to the crystal packing. For instance, for the para-nitro substituted derivative, Nit(p-NO2)Ph, which crystallizes in four different phases, the phase only orders ferromagnetically ( Tc = 0.6 K ) [8, 9]. Moreover, attaching the nitro group in the meta-, rather than the para-position of the phenyl, leads to an antiferromagnetic compound [2]. Furthermore, the NitR radicals have been shown to behave as valuable bridging ligands for obtaining low-dimensional, strongly coupled magnetic systems. Examples of high nuclearity Spin clusters, magnetic chains and magnetic planes have been reported in the course of a rather exhaustive investigation of complexes with 3d and 4f transition-metal hexafluoroacetylacetonates, M(hfac) n [10–14]. We report herein a single crystal polarized neutron investigation of the Spin Density of two purely organic nitronyl nitroxide free radicals which present ferromagnetic interactions: the 2-(6-ethynyl-2-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl3-oxide, NitPy(C C–H), and the 2-(4-methylthiophenyl)-4,4,5,5-tetramethylimidazoline1-oxyl-3-oxide, Nit(SMe)Ph. We have compared these results with the Spin Density of the NitPh [15] where the molecules are isolated one from the other, with practically no intermolecular magnetic interaction. The aryl group R of the NitPh, NitPy(C C–H) and Nit(SMe)Ph compounds are depicted in Figure 1B–D, respectively.

  • Spin Density of a ferromagnetic tempo derivative polarized neutron investigation and ab initio calculation
    Journal of Materials Chemistry, 2000
    Co-Authors: Y Pontillon, E Ressouche, Takayuki Ishida, Eddy Lelievreberna, Takashi Nogami, A Grand, J Schweizer
    Abstract:

    4(p-Chlorobenzylideneamino)-2,2,6,6-tetramethylpiperidine-N-oxyl is a ferromagnetic TEMPO derivative (Tc = 0.28 K) where the nearest and next nearest neighbour NO sites construct a two-dimensional network. We have determined the Spin Density in this compound by polarized neutron diffraction on a single crystal at low temperature. Most of the Spin Density (80%) has been found on the NO group, with an equal repartition between the two atoms. 20% of the Spin Density is delocalized on the rest of the molecule. As for the pure TEMPONE, the two carbon atoms neighbouring the nitrogen of the NO group carry significant Spin populations of different signs: −0.074(12) for C3 and +0.069(17) for C4. This implies that the coupling mechanism is rather complex: it concerns many contacts including methyl hydrogens, but also methylene hydrogens, the imino nitrogen N2 and the terminal chlorine atom. Ab initio (DFT) calculations account correctly for the repartition of the Spin Density between nitrogen and oxygen, but they underestimate the part of the Spin Density which is delocalized and also the effects of the magnetic interactions on the Spin populations of adjacent molecules.

  • Spin Density of a ferromagnetic tempo derivative
    Molecular Crystals and Liquid Crystals, 1999
    Co-Authors: Y Pontillon, E Ressouche, Takayuki Ishida, Eddy Lelievreberna, Takashi Nogami, J Schweizer
    Abstract:

    Abstract We have determined by polarized neutron diffraction the Spin Density of a ferromagnetic (Tc=0.28K) tempo derivative: the 4(p-chlorobenzylideneamino)-2,2,6,6-tetramethylpiperidin-1-oxyl, where the nearest and next nearest neighbours N-O sites construct a two-dimensional network parallel to the (a, b) plane. Most of the Spin Density lies on the N and O atoms of the NO radical and is equally shared between these two atoms. As for the pure tempone, the two carbon atoms neighbouring the nitrogen of the N-O group in the 6-member ring, carry significant Spin populations of different signs: -0.074(12) for atom C3 and ±0.063(17) for atom C4. This is not consistent with the coupling mechanism proposed previously which implied that the populations of both C3 and C4 should be negative. A tentative explanation for the coupling mechanisms, taking into account the Spin Density distribution, is discussed.

  • experimental and theoretical Spin Density in a ferromagnetic molecular complex
    Molecular Crystals and Liquid Crystals, 1999
    Co-Authors: Y Pontillon, E Ressouche, Eddy Lelievreberna, Takeyuki Akita, A Grand, Keiji Kobayashi, Jacques Pecaut, J Schweizer
    Abstract:

    Abstract The association of phenylboronic acid (no unpaired electron) with the free radical phenyl nitronyl nitroxide (S = 1/2) constitutes an inter-heteromolecular hydrogen bonding system presenting ferromagnetic intermolecular interactions. We have investigated its Spin Density distribution in order to visualize the pathway of these magnetic interactions. The Spin Density of this complex was measured by polarized neutron diffraction. The data were treated using both direct and indirect methods. As in the isolated PNN, the main part of the Spin Density is located on the O-N-C-N-O fragment of the PNN radical. But, with the PNNB, the global Spin Density distribution give evidences that the phenylboronic acid constitutes a Spin transmission path between PNN radicals via hydrogen bonds. The experimental results are compared to those obtained by Density functional theory calculations.

  • Spin Density in an enaminocetone nitroxide copper complex
    Molecular Crystals and Liquid Crystals, 1997
    Co-Authors: M Bonnet, Y Pontillon, E Ressouche, Jean Laugier, V I Ovcharenko, Paul Rey, P Schleger, J Schweizer
    Abstract:

    Abstract The copper complex C18H28O2N2Cu(NO)2 is a molecule which carries three Spins S=l/2. It crystallizes in the monoclinic space group Pc, with two molecules in the asymetric unit. Its χT starts to increase when the temperatures decreases, indicating ferromagnetic intramolecular coupling, and then, below T=40K, it completely collapses, showing negative coupling between molecules. We have investigated its Spin Density with polarized neutrons at T=40K and T=4.10K. At the higher temperature, the Spin Density is well localized on the Cu atom and the two NO groups of each molecule. At the lower temperature, the Spin Density exists, for each molecule, on the Cu atom and on one of the two NO groups only. There is a quasi dimerization on two NO groups, belonging to the different molecules, facing each other, and distant only by 3.40 A.

E K U Gross - One of the best experts on this subject based on the ideXlab platform.

  • transverse Spin gradient functional for noncollinear Spin Density functional theory
    Physical Review Letters, 2013
    Co-Authors: F. G. Eich, E K U Gross
    Abstract:

    : We present a novel functional for Spin-Density-functional theory aiming at the description of noncollinear magnetic structures. The construction of the functional employs the Spin-spiral-wave state of the uniform electron gas as reference system. We show that the functional depends on transverse gradients of the Spin magnetization; i.e., in contrast with the widely used local Spin Density approximation, the functional is sensitive to local changes of the direction of the Spin magnetization. As a consequence the exchange-correlation magnetic field is not parallel to the Spin magnetization and a local Spin torque is present in the ground state of the Kohn-Sham system. As a proof of principle, we apply the functional to a Chromium monolayer in the noncollinear 120°-Neel state.

  • comparison of exact exchange calculations for solids in current Spin Density and Spin Density functional theory
    Physical Review B, 2007
    Co-Authors: S Sharma, S Pittalis, S Kurth, S Shallcross, J K Dewhurst, E K U Gross
    Abstract:

    The relative merits of current-Spin-Density- and Spin-Density-functional theory are investigated for solids treated within the exact-exchange-only approximation. Spin-orbit splittings and orbital magnetic moments are determined at zero external magnetic field. We find that for magnetic (Fe, Co, and Ni) and nonmagnetic (Si and Ge) solids, the exact-exchange current-Spin-Density functional approach does not significantly improve the accuracy of the corresponding Spin-Density functional results.

Cenke Xu - One of the best experts on this subject based on the ideXlab platform.

  • fluctuating Spin Density waves in metals
    Physical Review B, 2009
    Co-Authors: Subir Sachdev, Max A Metlitski, Yang Qi, Cenke Xu
    Abstract:

    Recent work has used a U(1) gauge theory to describe the physics of Fermi pockets in the presence of fluctuating Spin Density wave order. We generalize this theory to an arbitrary band structure and ordering wave vector. The transition to the large Fermi-surface state, without pockets induced by local Spin Density wave order, is described by embedding the U(1) gauge theory in a SU(2) gauge theory. The phase diagram of the SU(2) gauge theory shows that the onset of Spin Density wave order in the Fermi liquid occurs either directly, in the framework discussed by Hertz, or via intermediate non-Fermi-liquid phases with Fermi surfaces of fractionalized excitations. We discuss application of our results to the phase diagram of the cuprates.

E Ressouche - One of the best experts on this subject based on the ideXlab platform.

  • Spin-Density distribution in the new molecular magnet p-O2N·C6F4·CNSSN
    Physica B-condensed Matter, 2003
    Co-Authors: Javier Luzón, E Ressouche, Javier Campo, Fernando Palacio, Garry J. Mcintyre, Andrés E. Goeta, Christopher M. Pask, Jeremy M. Rawson
    Abstract:

    Abstract Knowledge of the Spin-Density distribution in the dithiadiazolyl radical ring (DTDA) constitutes a major step towards the understanding of the magnetic and electronic properties of the rich magnetism of DTDA derivatives. The O 2 N·C 6 F 4 CNSSN radical was chosen as the most favourable CNSSN derivative to study the Spin distribution in this kind of free radicals by polarised-neutron diffraction. Spin-Density maps obtained for the O 2 N C 6 F 4 CNSSN radical show that almost all the Spin Density is localised on the sulphur and nitrogen atoms of the CNSSN ring. A small negative Spin Density on the carbon atom of the CNSSN ring and a negligible Spin Density over the rest of the radical are observed, in good agreement with ab initio calculations.

  • Spin Density of a ferromagnetic tempo derivative polarized neutron investigation and ab initio calculation
    Journal of Materials Chemistry, 2000
    Co-Authors: Y Pontillon, E Ressouche, Takayuki Ishida, Eddy Lelievreberna, Takashi Nogami, A Grand, J Schweizer
    Abstract:

    4(p-Chlorobenzylideneamino)-2,2,6,6-tetramethylpiperidine-N-oxyl is a ferromagnetic TEMPO derivative (Tc = 0.28 K) where the nearest and next nearest neighbour NO sites construct a two-dimensional network. We have determined the Spin Density in this compound by polarized neutron diffraction on a single crystal at low temperature. Most of the Spin Density (80%) has been found on the NO group, with an equal repartition between the two atoms. 20% of the Spin Density is delocalized on the rest of the molecule. As for the pure TEMPONE, the two carbon atoms neighbouring the nitrogen of the NO group carry significant Spin populations of different signs: −0.074(12) for C3 and +0.069(17) for C4. This implies that the coupling mechanism is rather complex: it concerns many contacts including methyl hydrogens, but also methylene hydrogens, the imino nitrogen N2 and the terminal chlorine atom. Ab initio (DFT) calculations account correctly for the repartition of the Spin Density between nitrogen and oxygen, but they underestimate the part of the Spin Density which is delocalized and also the effects of the magnetic interactions on the Spin populations of adjacent molecules.

  • Spin Density in interacting nitronyl nitroxide radicals
    2000
    Co-Authors: Y Pontillon, E Ressouche, Francisco M Romero, J Schweizer, Andrea Caneschi, Dante Gatteschi, Roberta Sessoli, Raymond Ziessel
    Abstract:

    Since the reported synthesis [1] of stable 2-phenyl-4,4,5,5-tetramethylimidazoline-1oxyl-3-oxide, NitPh, considerable effort has been spent in the physical characterization of nitronyl nitroxide compounds. Their general formula is presented in Figure 1A. These compounds carry a delocalized, S = 1/2, unpaired electron. Among them, some derivatives were found to be paramagnetic at low temperature (NitPh, [1]), others were found to exhibit an antiferromagnetic or a ferromagnetic behavior [2–7]. This magnetic behavior is very sensitive to the chemical structure of the Spin carrier and to the crystal packing. For instance, for the para-nitro substituted derivative, Nit(p-NO2)Ph, which crystallizes in four different phases, the phase only orders ferromagnetically ( Tc = 0.6 K ) [8, 9]. Moreover, attaching the nitro group in the meta-, rather than the para-position of the phenyl, leads to an antiferromagnetic compound [2]. Furthermore, the NitR radicals have been shown to behave as valuable bridging ligands for obtaining low-dimensional, strongly coupled magnetic systems. Examples of high nuclearity Spin clusters, magnetic chains and magnetic planes have been reported in the course of a rather exhaustive investigation of complexes with 3d and 4f transition-metal hexafluoroacetylacetonates, M(hfac) n [10–14]. We report herein a single crystal polarized neutron investigation of the Spin Density of two purely organic nitronyl nitroxide free radicals which present ferromagnetic interactions: the 2-(6-ethynyl-2-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl3-oxide, NitPy(C C–H), and the 2-(4-methylthiophenyl)-4,4,5,5-tetramethylimidazoline1-oxyl-3-oxide, Nit(SMe)Ph. We have compared these results with the Spin Density of the NitPh [15] where the molecules are isolated one from the other, with practically no intermolecular magnetic interaction. The aryl group R of the NitPh, NitPy(C C–H) and Nit(SMe)Ph compounds are depicted in Figure 1B–D, respectively.

  • Spin Density of a ferromagnetic tempo derivative
    Molecular Crystals and Liquid Crystals, 1999
    Co-Authors: Y Pontillon, E Ressouche, Takayuki Ishida, Eddy Lelievreberna, Takashi Nogami, J Schweizer
    Abstract:

    Abstract We have determined by polarized neutron diffraction the Spin Density of a ferromagnetic (Tc=0.28K) tempo derivative: the 4(p-chlorobenzylideneamino)-2,2,6,6-tetramethylpiperidin-1-oxyl, where the nearest and next nearest neighbours N-O sites construct a two-dimensional network parallel to the (a, b) plane. Most of the Spin Density lies on the N and O atoms of the NO radical and is equally shared between these two atoms. As for the pure tempone, the two carbon atoms neighbouring the nitrogen of the N-O group in the 6-member ring, carry significant Spin populations of different signs: -0.074(12) for atom C3 and ±0.063(17) for atom C4. This is not consistent with the coupling mechanism proposed previously which implied that the populations of both C3 and C4 should be negative. A tentative explanation for the coupling mechanisms, taking into account the Spin Density distribution, is discussed.

  • experimental and theoretical Spin Density in a ferromagnetic molecular complex
    Molecular Crystals and Liquid Crystals, 1999
    Co-Authors: Y Pontillon, E Ressouche, Eddy Lelievreberna, Takeyuki Akita, A Grand, Keiji Kobayashi, Jacques Pecaut, J Schweizer
    Abstract:

    Abstract The association of phenylboronic acid (no unpaired electron) with the free radical phenyl nitronyl nitroxide (S = 1/2) constitutes an inter-heteromolecular hydrogen bonding system presenting ferromagnetic intermolecular interactions. We have investigated its Spin Density distribution in order to visualize the pathway of these magnetic interactions. The Spin Density of this complex was measured by polarized neutron diffraction. The data were treated using both direct and indirect methods. As in the isolated PNN, the main part of the Spin Density is located on the O-N-C-N-O fragment of the PNN radical. But, with the PNNB, the global Spin Density distribution give evidences that the phenylboronic acid constitutes a Spin transmission path between PNN radicals via hydrogen bonds. The experimental results are compared to those obtained by Density functional theory calculations.

Subir Sachdev - One of the best experts on this subject based on the ideXlab platform.

  • fluctuating Spin Density waves in metals
    Physical Review B, 2009
    Co-Authors: Subir Sachdev, Max A Metlitski, Yang Qi, Cenke Xu
    Abstract:

    Recent work has used a U(1) gauge theory to describe the physics of Fermi pockets in the presence of fluctuating Spin Density wave order. We generalize this theory to an arbitrary band structure and ordering wave vector. The transition to the large Fermi-surface state, without pockets induced by local Spin Density wave order, is described by embedding the U(1) gauge theory in a SU(2) gauge theory. The phase diagram of the SU(2) gauge theory shows that the onset of Spin Density wave order in the Fermi liquid occurs either directly, in the framework discussed by Hertz, or via intermediate non-Fermi-liquid phases with Fermi surfaces of fractionalized excitations. We discuss application of our results to the phase diagram of the cuprates.