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 Mn$_3$Ir and Mn$_3$Sn, 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