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Sökning: WAKA:ref > Eriksson Olle > Lizárraga Raquel

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1.
  • Björkman, Torbjörn, 1977-, et al. (författare)
  • Theoretical studies of the incommensurate magnetic structure of a heavy fermion system: CeRhIn5
  • 2010
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 81:9, s. 094433
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the electronic structure and the incommensurate magnetic configuration of the pressure-induced superconductor CeRhIn5. Noncollinear first-principles calculations were performed in the local-density approximation plus U scheme. The observed magnetic configuration is described accurately in our calculations, especially considering the minute energy scale which is relevant (microelectron volt). The band structure and Fermi surfaces were investigated and nesting was found to be responsible for the complex noncollinear magnetic state of CeRhIn5.
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2.
  • Eriksson, T., et al. (författare)
  • Crystal and magnetic structure of Mn3IrSi
  • 2004
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 69:5, s. 054422
  • Tidskriftsartikel (refereegranskat)abstract
    • A new ternary Ir-Mn-Si phase with stoichiometry Mn3IrSi has been synthesized and found to crystallize in the cubic AlAu4-type structure, space group P213 with Z=4, which is an ordered form of the β-Mn structure. The unit cell dimension was determined by x-ray powder diffraction to a=6.4973(3)Å. In addition to the crystal structure, we have determined the magnetic structure and properties using superconducting quantum interference device magnetometry and Rietveld refinements of neutron powder diffraction data. A complex noncollinear magnetic structure is found, with magnetic moments of 2.97(4)μB at 10 K only on the Mn atoms. The crystal structure consists of a triangular network built up by Mn atoms, on which the moments are rotated 120° around the triangle axes. The magnetic unit cell is the same as the crystallographic and carries no net magnetic moment. The Néel temperature was determined to be 210 K. A first-principles study, based on density functional theory in a general noncollinear formulation, reproduces the experimental results with good agreement. The observed magnetic structure is argued to be the result of frustration of antiferromagnetic couplings by the triangular geometry.
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3.
  • Eriksson, Therese, et al. (författare)
  • Crystal structure and magnetic properties of the new phase Mn3IrSi
  • 2004
  • Ingår i: Journal of Magnetism and Magnetic Materials. ; :272-276, s. 823-825
  • Tidskriftsartikel (refereegranskat)abstract
    • A new phase in the ternary Ir–Mn–Si system has been synthesised. From powder neutron diffraction data the crystal structure was determined to be of the AlAu4 type and to be described in the cubic space group P213 with the unit cell a=6.4973(3) Å. Susceptibility measurements using a SQUID-magnetometer showed a transition typical of antiferromagnetism, with TN=210 K. Low temperature antiferromagnetic order is confirmed by extra peaks in neutron diffractograms recorded at 10 and 80 K.
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4.
  • Holmstroem, Erik, et al. (författare)
  • Disorder-induced metallicity in amorphous graphene
  • 2011
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 84:20, s. 205414
  • Tidskriftsartikel (refereegranskat)abstract
    • We predict a transition to metallicity when a sufficient amount of disorder is induced in graphene. Calculations were performed by means of a first-principles stochastic quench method. The resulting amorphous graphene can be seen as nanopatches of graphene that are connected by a network of disordered small and large carbon rings. The buckling of the lattice is minimal and is a result of averaging of counteracting random in-plane stress forces. The linear response conductance is obtained by a model theory as function of lattice distortions, and results in a similar behavior as the first-principles calculation.
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6.
  • Lizárraga, Raquel, et al. (författare)
  • Conditions for noncollinear instabilities of ferromagnetic materials
  • 2004
  • Ingår i: Physical Review Letters. - 0031-9007. ; 93:10, s. 107205
  • Tidskriftsartikel (refereegranskat)abstract
    • Two criteria have been identified here which determine whether a magnetic metal orders in a collinear (e.g., ferromagnet) or noncollinear (e.g., spin-spiral) arrangement. These criteria involve the ratio between the strength of the exchange interaction and the width of the electron bands, as well as Fermi-surface nesting between spin-up and spin-down sheets of the Fermi surface. Based on our analysis we predict that even typical ferromagnetic materials (e.g., Fe, Co, and Ni) should be possible to stabilize in a noncollinear magnetic order in, e.g., high pressure experiments.
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7.
  • Lizárraga, Raquel, et al. (författare)
  • Crystal and magnetic structure investigation of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0) : Experiment and theory
  • 2006
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 74:9, s. 094419
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of Cu substitution on the structural and magnetic properties of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0) have been investigated by x-ray diffraction, magnetization measurements and neutron powder and single crystal diffraction. The electronic and the magnetic structures of TbNi5 were studied using first principles theory. All samples were found to have the CaCu5-type structure, space group P6/mmm. The lattice parameters increase monotonically with increasing Cu concentration. The Curie temperature T-c has a maximum value of 29 K at x=1.0. The magnetic structure of TbNi5 at 10 K is incommensurate with a helimagnetic component [wave vector q similar to 2 pi/c(0,0,0.02)] perpendicular to a ferromagnetic one. In contrast, the substituted TbNi5-xCux alloy is ferromagnetic. All magnetic moments are observed to be located on the Tb atoms. The magnetocrystalline anisotropy in the ab plane is observed to be strongly increased by the Cu substitution, whereas the magnetization decreases with the Cu concentration. The observed magnetic structure of TbNi5 is consistent with first principles calculations regarding both the magnetic moments and the helimagnetic structure. The microscopical origin of the helimagnet is analyzed and correlated to the Fermi surface topology.
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8.
  • Lizarraga, Raquel, et al. (författare)
  • Noncollinear magnetism in the high-pressure hcp phase of iron
  • 2008
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 78:6, s. 064410
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetic structure of iron in its high-pressure hcp phase has been investigated with the full-potential augmented plane wave with local orbitals method that allows for noncollinear magnetism. In our study we consider different spin spiral structures and, three antiferromagnetic configurations that have been previously discussed in the literature. We found that some of the magnetic structures are only metastable, and that a nonsymmetric incommensurate spin spiral state with wave vector q = (0.56, 0.22, 0)2 pi/a and two different antiferromagnetic structures are the most stable ones being almost degenerate around the equilibrium volume. These magnetic structures ought to exist in the pressure range where hcp iron becomes stable.
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9.
  • Lizarraga, Raquel, et al. (författare)
  • Noncollinear spin states in TlCo2Se2-xSx alloys from first principles
  • 2007
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 75:2, s. 024425
  • Tidskriftsartikel (refereegranskat)abstract
    • The observed transition of the magnetic structure from a noncollinear state at x=0 to a ferromagnetic phase at x=1.75, through a series of spin spirals in the substitutional TlCo2Se2-xSx alloys, has been investigated by first principles theory. Our calculations successfully reproduced the magnetic structure of TlCo2S2 and the obtained magnetic moment is somewhat higher (0.82 mu(beta) per Co atom) than the experimental value. However, TlCo2Se2 was found to possess an antiferromagnetic state which is inconsistent with the observed spin spiral. We show that the correct magnetic structure of TlCo2Se2 can be obtained if the distance between the Co layers is reduced. Moreover, we demonstrate that the modification of the Co interlayer distance is a crucial parameter that governs the nature of the magnetism in these alloys. We discuss a mechanism that could favor noncollinear states in TlCo2Se2 over the ferromagnetic configuration and explain the change of the magnetic structure in the substitutional TlCo2Se2-xSx alloys.
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10.
  • Lizárraga, Raquel, et al. (författare)
  • On the magnetic structure of TlCo2Se2
  • 2004
  • Ingår i: Journal of Magnetism and Magnetic Materials. - 0304-8853. ; 272:557, s. 272-276
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetic properties of TlCo2Se2 have been investigated by means of first principles calculations. The magnetism of this compound is dominated by the contribution from the Co atoms, which form layers with a square coordination. The magnetic moments are arranged ferromagnetically within the ab-plane and in a non-collinear manner between consecutive planes.
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