Symmetry conditions for type II multiferroicity in commensurate magnetic structures

Elastic moduli from crystalline micro-mechanical oscillators carved by focused ion beam

The elastic moduli provide unique insights into the thermodynamics of quantum materials, particularly into the symmetries broken at their phase transition. Here, we present a workflow to carve crystalline resonators via focused ion beam milling from small and oddly shaped crystals unsuitable for traditional measurements of elasticity. The accuracy of this technique is first established in silicon. Next, we showcase the capacity to probe changes in the electronic state with a resolution on the measured resonance frequency as small as 0.01% on YNiO3, a rare-earth perovskite nickelate, in which bulk single crystals have typical length scales of ≈40μm. Here, we observe a sharp 0.2% discontinuity in Young's modulus of an YNiO3 cantilever at a magnetic phase transition. Finally, an additional potential of using free-standing cantilevers as a tool for examining the time-dependence of chemical changes is illustrated by laser-heating YNiO3.

Magnetic modes compatible with the symmetry of crystals

A classification of magnetic point groups is presented which gives an answer to the question: which magnetic groups can describe a given magnetic mode? There are 32 categories of magnetic point groups which describe 64 unique magnetic modes: 16 with a ferromagnetic component and 48 without. This classification focused on magnetic modes is helpful for finding the magnetic space group which can describe the magnetic symmetry of the material.

Synthesis, Structure, and Physical Properties of the Polar Magnet DyCrWO6

It has recently been reported that the ordered aeschynite-type polar ( Pna2₁) magnets RFeWO₆ (R = Eu, Tb, Dy, Y) exhibit type II multiferroic properties below T_N ∼ 15-18 K. Herein, we report a comprehensive investigation of the isostructural oxide DyCrWO₆ and compare the results with those of DyFeWO₆. The cation-ordered oxide DyCrWO₆ crystallizes in the same polar orthorhombic structure and undergoes antiferromagnetic ordering at T_N = 25 K. Contrary to DyFeWO₆, only a very weak dielectric anomaly and magnetodielectric effects are observed at the Néel temperature and, more importantly, there is no induced polarization at T_N. Furthermore, analysis of the low-temperature neutron diffraction data reveals a collinear arrangement of Cr spins but a noncollinear Dy-spin configuration due to single-ion anisotropy. We suggest that the collinear arrangement of Cr spins may be responsible for the absence of electric polarization in DyCrWO₆. A temperature-induced magnetization reversal and magnetocaloric effects are observed at low temperatures.

MAGNDATA: towards a database of magnetic structures. I. The commensurate case

A free web page under the name MAGNDATA, which provides detailed quantitative information on more than 400 published magnetic structures, has been developed and is available at the Bilbao Crystallographic Server (http://www.cryst.ehu.es). It includes both commensurate and incommensurate structures. This first article is devoted to explaining the information available on commensurate magnetic structures. Each magnetic structure is described using magnetic symmetry, i.e. a magnetic space group (or Shubnikov group). This ensures a robust and unambiguous description of both atomic positions and magnetic moments within a common unique formalism. A non-standard setting of the magnetic space group is often used in order to keep the origin and unit-cell orientation of the paramagnetic phase, but a description in any desired setting is possible. Domain-related equivalent structures can also be downloaded. For each structure its magnetic point group is given, and the resulting constraints on any macroscopic tensor property of interest can be consulted. Any entry can be retrieved as a magCIF file, a file format under development by the International Union of Crystallography. An online visualization tool using Jmol is available, and the latest versions of VESTA and Jmol support the magCIF format, such that these programs can be used locally for visualization and analysis of any of the entries in the collection. The fact that magnetic structures are often reported without identifying their symmetry and/or with ambiguous information has in many cases forced a reinterpretation and transformation of the published data. Most of the structures in the collection possess a maximal magnetic symmetry within the constraints imposed by the magnetic propagation vector(s). When a lower symmetry is realized, it usually corresponds to an epikernel (isotropy subgroup) of one irreducible representation of the space group of the parent phase. Various examples of the structures present in this collection are discussed.