33 research outputs found
High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt
YbBiPt is a heavy-fermion compound possessing significant short-range
antiferromagnetic correlations below a temperature of K,
fragile antiferromagnetic order below K, a Kondo temperature
of K, and crystalline-electric-field splitting on the
order of K. Whereas the compound has a
face-centered-cubic lattice at ambient temperature, certain experimental data,
particularly those from studies aimed at determining its
crystalline-electric-field scheme, suggest that the lattice distorts at lower
temperature. Here, we present results from high-resolution, high-energy x-ray
diffraction experiments which show that, within our experimental resolution of
\AA, no structural phase transition
occurs between and K. In combination with results from dilatometry
measurements, we further show that the compound's thermal expansion has a
minimum at K and a region of negative thermal expansion for
K. Despite diffraction patterns taken at K which indicate that
the lattice is face-centered cubic and that the Yb resides on a
crystallographic site with cubic point symmetry, we demonstrate that the linear
thermal expansion may be modeled using crystalline-electric-field level schemes
appropriate for Yb residing on a site with either cubic or less than
cubic point symmetry.Comment: 7 pages, 3 figures, submitted to Phys. Rev.
Controlling Magnetic Order, Magnetic Anisotropy, and Band Topology in Semimetals and
Neutron diffraction and magnetic susceptibility studies show that
orthorhombic single-crystals of topological semimetals and undergo three
dimensional C-type antiferromagnetic (AFM) ordering of the Mn moments at
and K, respectively, significantly lower than that
of the parent SrMnSb with K. Magnetization versus applied
magnetic field (perpendicular to MnSb planes) below exhibits slightly
modified de Haas van Alphen oscillations for the Zn-doped crystal as compared
to that of the parent compound. By contrast, the Cu-doped system does not show
de Haas van Alphen magnetic oscillations, suggesting that either Cu
substitution for Mn changes the electronic structure of the parent compound
substantially, or that the Cu sites are strong scatterers of carriers that
significantly shorten their mean free path thus diminishing the oscillations.
Density functional theory (DFT) calculations including spin-orbit coupling
predict the C-type AFM state for the parent, Cu-, and Zn-doped systems and
identify the -axis (i.e., perpendicular to the Mn layer) as the easy
magnetization direction in the parent and 12.5% of Cu or Zn substitutions. In
contrast, 25% of Cu content changes the easy magnetization to the -axis
(i.e., within the Mn layer). We find that the incorporation of Cu and Zn in
SrMnSb tunes electronic bands near the Fermi level resulting in different
band topology and semi-metallicity. The parent and Zn-doped systems have
coexistence of electron and hole pockets with opened Dirac cone around the
Y-point whereas the Cu-doped system has dominant hole pockets around the Fermi
level with a distorted Dirac cone. The tunable electronic structure may point
out possibilities of rationalizing the experimentally observed de Haas van
Alphen magnetic oscillations
Competing magnetic fluctuations and orders in a multiorbital model of doped SrCoAs
We revisit the intriguing magnetic behavior of the paradigmatic itinerant
frustrated magnet , which shows strong and competing
magnetic fluctuations yet does not develop long-range magnetic order. By
calculating the static spin susceptibility within a
realistic sixteen orbital Hubbard-Hund model, we determine the leading
instability to be ferromagnetic (FM). We then explore the effect of doping and
calculate the critical Hubbard interaction strength that is required for
the development of magnetic order. We find that decreases under electron
doping and with increasing Hund's coupling , but increases rapidly under
hole doping. This suggests that magnetic order could possibly emerge under
electron doping but not under hole doping, which agrees with experimental
findings. We map out the leading magnetic instability as a function of doping
and Hund's coupling and find several antiferromagnetic phases in addition to
FM. We also quantify the degree of itinerant frustration in the model and
resolve the contributions of different orbitals to the magnetic susceptibility.
Finally, we discuss the dynamic spin susceptibility, , at finite frequencies, where we recover the anisotropy of the peaks
at and observed by inelastic neutron
scattering that is associated with the phenomenon of itinerant magnetic
frustration. By comparing results between theory and experiment, we conclude
that the essential experimental features of doped SrCoAs are well
captured by a Hubbard-Hund multiorbital model if one considers a small shift of
the chemical potential towards hole doping.Comment: 19 pages, 12 figure
Nitrogen Contamination in Elastic Neutron Scattering
Nitrogen gas accidentally sealed in a sample container produces various
spurious effects in elastic neutron scattering measurements. These effects are
systematically investigated and the details of the spurious scattering are
presented
Pressure-induced collapsed-tetragonal phase in SrCo2As2
We present high-energy x-ray diffraction data under applied pressures up to p
= 29 GPa, neutron diffraction measurements up to p = 1.1 GPa, and electrical
resistance measurements up to p = 5.9 GPa, on SrCo2As2. Our x-ray diffraction
data demonstrate that there is a first-order transition between the tetragonal
(T) and collapsed-tetragonal (cT) phases, with an onset above approximately 6
GPa at T = 7 K. The pressure for the onset of the cT phase and the range of
coexistence between the T and cT phases appears to be nearly temperature
independent. The compressibility along the a-axis is the same for the T and cT
phases whereas, along the c-axis, the cT phase is significantly stiffer, which
may be due to the formation of an As-As bond in the cT phase. Our resistivity
measurements found no evidence of superconductivity in SrCo2As2 for p <= 5.9
GPa and T >= 1.8 K. The resistivity data also show signatures consistent with a
pressure-induced phase transition for p >= 5.5 GPa. Single-crystal neutron
diffraction measurements performed up to 1.1 GPa in the T phase found no
evidence of stripe-type or A-type antiferromagnetic ordering down to 10 K.
Spin-polarized total-energy calculations demonstrate that the cT phase is the
stable phase at high pressure with a c/a ratio of 2.54. Furthermore, these
calculations indicate that the cT phase of SrCo2As2 should manifest either
A-type antiferromagnetic or ferromagnetic order.Comment: 6 pages, 5 figure
Zero-field magnetic ground state of EuMg2 Bi2
Layered trigonal EuMg2Bi2 is reported to be a topological semimetal that hosts multiple Dirac points that may be gapped or split by the onset of magnetic order. Here, we report zero-field single-crystal neutron-diffraction and bulk magnetic susceptibility measurements versus temperature χ(T) of EuMg2Bi2 that show the intraplane ordering is ferromagnetic (Eu2+,S=7/2) with the moments aligned in the ab plane while adjacent layers are aligned antiferromagnetically (i.e., A-type antiferromagnetism) below the Néel temperature
Strong cooperative coupling of pressure-induced magnetic order and nematicity in FeSe
A hallmark of the iron-based superconductors is the strong coupling between magnetic, structural and electronic degrees of freedom. However, a universal picture of the normal state properties of these compounds has been confounded by recent investigations of FeSe where the nematic (structural) and magnetic transitions appear to be decoupled. Here, using synchrotron-based high-energy x-ray diffraction and time-domain Mössbauer spectroscopy, we show that nematicity and magnetism in FeSe under applied pressure are indeed strongly coupled. Distinct structural and magnetic transitions are observed for pressures between 1.0 and 1.7 GPa and merge into a single first-order transition for pressures ≳1.7 GPa, reminiscent of what has been found for the evolution of these transitions in the prototypical system Ba(Fe1−xCox)2As2. Our results are consistent with a spin-driven mechanism for nematic order in FeSe and provide an important step towards a universal description of the normal state properties of the iron-based superconductors