80 research outputs found
Nearest neighbor exchange in Co- and Mn-doped ZnO
We calculate the magnetic interactions between two nearest neighbor substitutional magnetic ions (Co or Mn) in ZnO by means of density functional theory and compare it with the available experimental data. Using the local spin density approximation we find a coexistence of ferro- and antiferromagnetic couplings for ZnO:Co, in contrast to experiment. For ZnO:Mn both couplings are antiferromagnetic but deviate quantitatively from measurement. That points to the necessity to account better for the strong electron correlation at the transition ion site which we have done by applying the LSDA+U method. We show that we have to distinguish two different nearest neighbor exchange integrals for the two systems in question which are all antiferromagnetic with values between -1.0 and -2.0 meV in reasonable agreement with experiment
Band dependent emergence of heavy quasiparticles in CeCoIn5
We investigate the low temperature (T 2 K) electronic structure of the
heavy fermion superconductor CeCoIn5 (T = 2.3 K) by angle-resolved
photoemission spectroscopy (ARPES). The hybridization between conduction
electrons and f-electrons, which ultimately leads to the emergence of heavy
quasiparticles responsible for the various unusual properties of such
materials, is directly monitored and shown to be strongly band dependent. In
particular the most two-dimensional band is found to be the least hybridized
one. A simplified multiband version of the Periodic Anderson Model (PAM) is
used to describe the data, resulting in semi-quantitative agreement with
previous bulk sensitive results from de-Haas-van-Alphen measurements.Comment: 6 pages, 3 figure
Distinct magnetic regimes through site-selective atom substitution in the frustrated quantum antiferromagnet CsCuClBr
We report on a systematic study of the magnetic properties on single crystals
of the solid solution CsCuClBr (0 x 4), which
include the two known end-member compounds CsCuCl and CsCuBr,
classified as quasi-two-dimensional quantum antiferromagnets with different
degrees of magnetic frustration. By comparative measurements of the magnetic
susceptibility () on as many as eighteen different Br concentrations,
we found that the inplane and out-of-plane magnetic correlations, probed by the
position and height of a maximum in the magnetic susceptibility, respectively,
do not show a smooth variation with x. Instead three distinct concentration
regimes can be identified, which are separated by critical concentrations
x = 1 and x = 2. This unusual magnetic behavior can be explained
by considering the structural peculiarities of the materials, especially the
distorted Cu-halide tetrahedra, which support a site-selective replacement of
Cl- by Br- ions. Consequently, the critical concentrations x (x)
mark particularly interesting systems, where one (two) halidesublattice
positions are fully occupied.Comment: 15 pages, 4 figure
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Magnetic-field- and temperature-dependent fermi surface of CeBiPt
The half-Heusler compounds CeBiPt and LaBiPt are semimetals with very low charge-carrier concentrations as evidenced by Shubnikovâde Haas (SdH) and Hall-effect measurements. Neutron-scattering results reveal a simple antiferromagnetic structure in CeBiPt below TN = 1.15âK. The band structure of CeBiPt sensitively depends on temperature, magnetic field and stoichiometry. Above a certain, sample-dependent, threshold field (B>25âT), the SdH signal disappears and the Hall coefficient reduces significantly. These effects are absent in the non-4f compound LaBiPt. Electronic-band-structure calculations can well explain the observed behaviour by a 4f-polarization-induced Fermi-surface modification
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Magnetic-field- and temperature-dependent fermi surface of CeBiPt
The half-Heusler compounds CeBiPt and LaBiPt are semimetals with very low charge-carrier concentrations as evidenced by Shubnikovâde Haas (SdH) and Hall-effect measurements. Neutron-scattering results reveal a simple antiferromagnetic structure in CeBiPt below TN = 1.15âK. The band structure of CeBiPt sensitively depends on temperature, magnetic field and stoichiometry. Above a certain, sample-dependent, threshold field (B>25âT), the SdH signal disappears and the Hall coefficient reduces significantly. These effects are absent in the non-4f compound LaBiPt. Electronic-band-structure calculations can well explain the observed behaviour by a 4f-polarization-induced Fermi-surface modification
Tuning of crystal structure and magnetic properties by exceptionally large epitaxial strains
Huge deformations of the crystal lattice can be achieved in materials with
inherent structural instability by epitaxial straining. By coherent growth on
seven different substrates the in-plane lattice constants of 50 nm thick
Fe70Pd30 films are continuously varied. The maximum epitaxial strain reaches
8,3 % relative to the fcc lattice. The in-plane lattice strain results in a
remarkable tetragonal distortion ranging from c/abct = 1.09 to 1.39, covering
most of the Bain transformation path from fcc to bcc crystal structure. This
has dramatic consequences for the magnetic key properties. Magnetometry and
X-ray circular dichroism (XMCD) measurements show that Curie temperature,
orbital magnetic moment, and magnetocrystalline anisotropy are tuned over broad
ranges.Comment: manuscript, 3 figures, auxiliary materia
The electronic structure of CeCoIn5 from angle-resolved photoemission spectroscopy I: Comparison to LDA
We have investigated the low-energy electronic structure of the heavy fermion
superconductor CeCoIn5 by angle-resolved photoemission and band structure
calculations. We measured the Fermi surface and energy distribution maps along
the high-symmetry directions at hn = 100 eV and T = 25 K. The compound has
quasi two-dimensional Fermi surface sheets centered at the M-A line of the
Brillouin zone. The band structure calculations have been carried out within
the local density approximation where the 4f electrons have been treated either
localized or itinerant. We discuss the comparison to the experimental data and
the implications for the nature of the 4f electrons at the given temperature.Comment: 21 pages, 5 figure
Electron penetration in the nucleus and its effect on the quadrupole interaction
A series expansion of the interaction between a nucleus and its surrounding
electron distribution provides terms that are well-known in the study of
hyperfine interactions: the familiar quadrupole interaction and the less
familiar hexadecapole interaction. If the penetration of electrons into the
nucleus is taken into account, various corrections to these multipole
interactions appear. The best known one is a scalar correction related to the
isotope shift and the isomer shift. This paper discusses a related tensor
correction, which modifies the quadrupole interaction if electrons penetrate
the nucleus: the quadrupole shift. We describe the mathematical formalism and
provide first-principles calculations of the quadrupole shift for a large set
of solids. Fully relativistic calculations that explicitly take a finite
nucleus into account turn out to be mandatory. Our analysis shows that the
quadrupole shift becomes appreciably large for heavy elements. Implications for
experimental high-precision studies of quadrupole interactions and quadrupole
moment ratios are discussed. A literature review of other small quadrupole-like
effects is presented as well
Interface effects on the magnetic properties of layered Ni<sub>2</sub>MnGa/Ni<sub>2</sub>MnSn alloys: A first-principles investigation
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