30 research outputs found
First-principles theory of multipolar order in actinide dioxides
AbstractMagnetic phase transitions that involve multipolar degrees of freedom have been widely studied during the last couple of decades, challenging the common approximation which assumes that the physical properties of a magnetic material could be effectively described by purely dipolar degrees of freedom. Due to the complexity of the problem and to the large number of competing interactions involved, the simple (fcc) crystal structure of the actinide dioxides made them the ideal playground system for such theoretical and experimental studies. In the present paper, we summarize our recent attempts to provide an ab initio description of the ordered phases of UO2, NpO2, and AmO2 by means of state-of-the-art LDA+U first-principles calculations. This systematic analysis of the electronic structures is here naturally connected to the local crystalline fields of the 5f states in the actinide dioxide series. Related to these we find that the mechanisms which lead to the experimentally observed insulating ground states work in distinctly different ways for each compound
High-performance descriptor for magnetic materials:Accurate discrimination of magnetic symmetries
The magnetic structure is crucial in determining the physical properties
inherent in magnetic compounds. We present an adequate descriptor for magnetic
structure with proper magnetic symmetry and high discrimination performance,
which does not depend on artificial choices for coordinate origin, axis, and
magnetic unit cell in crystal. We extend the formalism called ``smooth overlap
of atomic positions'' (SOAP) providing a numerical representation of atomic
configurations to that of magnetic moment configurations. We introduce the
descriptor in terms of the vector spherical harmonics to describe a magnetic
moment configuration and partial spectra from the expansion coefficients. We
discuss that the lowest order partial spectrum is insufficient to discriminate
the magnetic structures with different magnetic anisotropy, and a higher order
partial spectrum is required in general to characterize detailed magnetic
structures on the same atomic configuration. We then introduce the fourth-order
partial spectrum and evaluate the discrimination performance for different
magnetic structures, mainly focusing on the difference in magnetic symmetry.
The modified partial spectra that are defined not to reflect the difference of
magnetic anisotropy are also useful in evaluating magnetic structures obtained
from first-principles calculations without spin-orbit coupling. We apply the
present method to the symmetry-classified magnetic structures for the crystals
of MnIr and MnSn, which are known to exhibit anomalous transport under
the antiferromagnetic order, and examine the discrimination performance of the
descriptor for different magnetic structures on the same crystal.Comment: 13 pages including supplementary information, 8 figure
High-throughput calculations of antiferromagnets hosting anomalous transport phenomena
We develop a high-throughput computational scheme based on cluster multipole
theory to identify new functional antiferromagnets. This approach is applied to
228 magnetic compounds listed in the AtomWork-Adv database, known for their
elevated N\'eel temperatures. We conduct systematic investigations of both
stable and metastable magnetic configurations of these materials. Our findings
reveal that 34 of these compounds exhibit antiferromagnetic structures with
zero propagation vectors and magnetic symmetries identical to conventional
ferromagnets, rendering them potentially invaluable for spintronics
applications. By cross-referencing our predictions with the existing MAGNDATA
database and published literature, we verify the reliability of our findings
for 26 out of 28 compounds with partially or fully elucidated magnetic
structures in the experiments. These results not only affirm the reliability of
our scheme but also point to its potential for broader applicability in the
ongoing quest for the discovery of new functional magnets.13Comment: 13 pages, 1 figur