Magnetostriction-polarization coupling in multiferroic Mn2MnWO6

Double corundum-related polar magnets are promising materials for multiferroic and magnetoelectric applications in spintronics. However, their design and synthesis is a challenge, and magnetoelectric coupling has only been observed in Ni3TeO6 among the known double corundum compounds to date. Here we address the high-pressure synthesis of a new polar and antiferromagnetic corundum derivative Mn2MnWO6, which adopts the Ni3TeO6-type structure with low temperature first-order field-induced metamagnetic phase transitions (T N = 58 K) and high spontaneous polarization (~ 63.3 μC·cm−2). The magnetostriction-polarization coupling in Mn2MnWO6 is evidenced by second harmonic generation effect, and corroborated by magnetic-field-dependent pyroresponse behavior, which together with the magnetic-field-dependent polarization and dielectric measurements, qualitatively indicate magnetoelectric coupling. Piezoresponse force microscopy imaging and spectroscopy studies on Mn2MnWO6 show switchable polarization, which motivates further exploration on magnetoelectric effect in single crystal/thin film specimens

Spatio-Temporal Symmetry—Point Groups with Time Translations

Spatial symmetries occur in combination with temporal symmetries in a wide range of physical systems in nature, including time-periodic quantum systems typically described by the Floquet formalism. In this context, groups formed by three-dimensional point group symmetry operations in combination with time translation operations are discussed in this work. The derivation of these ’spatio-temporal’ groups from conventional point groups and their irreducible representations is outlined, followed by a complete listing. The groups are presented in a template similar to space group operations, and are visualized using a modified version of conventional stereographic projections. Simple examples of physical processes that simultaneously exhibit symmetry in space and time are identified and used to illustrate the application of spatio-temporal groups

Linear and nonlinear optical probe of the ferroelectric-like phase transition in a polar metal, LiOsO 3

LiOsO3 is one of the first materials identified in a recent literature as a 'polar metal', a class of materials that are simultaneously noncentrosymmetric and metallic. In this work, the linear and nonlinear optical susceptibility of LiOsO3 is studied by means of ellipsometry and optical second harmonic generation (SHG). Strong optical birefringence is observed using spectroscopic ellipsometry. The nonlinear optical susceptibility extracted from SHG polarimetry reveals that the tensor components are of the same magnitude as in isostructural insulator LiNbO3, except the component along the polar axis d33, which is suppressed by an order of magnitude. Temperature-dependent SHG measurements in combination with Raman spectroscopy indicate a continuous order-disorder type polar phase transition at 140 K. Linear and nonlinear optical microscopy techniques reveal 109 deg/71 deg ferroelastic domain walls, like in other trigonal ferroelectrics. No 180 deg polar domain walls are observed to emerge across the phase transition.Comment: Supplementary material in ancillary file

A(II)GeTeO₆ (A = Mn, Cd, Pb): Non-Centrosymmetric Layered Tellurates with PbSb₂O₆‑Related Structure

A­(II)­GeTeO₆ (A = Mn, Cd, Pb), new non-centrosymmetric (NCS) honeycomb-layered tellurates, were synthesized and characterized. A­(II)­GeTeO₆ (A = Mn, Cd, Pb) crystallize in trigonal space group <i>P</i>312 (No. 149) of edge-sharing Ge⁴⁺O₆ and Te⁶⁺O₆ octahedra, which form honeycomb-like-layers in the <i>ab</i>-plane with A­(II) (A = Mn, Cd, Pb) cations located between the layers. Their crystal structures are PbSb₂O₆-related, and the ordering of Ge⁴⁺ and Te⁶⁺ in octahedral environment breaks the inversion symmetry of the parent PbSb₂O₆ structure. The size of A­(II) cation in six coordination is an important factor to stabilize PbSb₂O₆-based structure. Temperature-dependent optical second harmonic generation measurements on A­(II)­GeTeO₆ confirmed non-centrosymmetric character in the entire scanned temperature range (0 to 600 °C). The materials exhibit a powder SHG efficiency of ∼0.37 and ∼0.21 times of KH₂PO₄ for PbGeTeO₆ and CdGeTeO₆, respectively. Magnetic measurements of MnGeTeO₆ indicate anti-ferromagnetic order at <i>T</i>_N ≈ 9.4 K with Weiss temperature of −22.47 K

Hybrid Improper Ferroelectricity in (Sr,Ca)SnO and Beyond Universal Relationship between Ferroelectric Transition Temperature and Tolerance Factor in n = 2 Ruddlesden-Popper Phases

International audienceHybrid improper ferroelectricity, which utilizes nonpolar but ubiquitous rotational/tilting distortions to create polarization, offers an attractive route to the discovery of new ferroelectric and multiferroic materials because its activity derives from geometric rather than electronic origins. Design approaches blending group theory and first principles can be utilized to explore the crystal symmetries of ferroelectric ground states, but in general, they do not make accurate predictions for some important parameters of ferroelectrics, such as Curie temperature ( T). Here, we establish a predictive and quantitative relationship between T and the Goldschmidt tolerance factor, t, by employing n = 2 Ruddlesden-Popper (RP) ABO as a prototypical example of hybrid improper ferroelectrics. The focus is placed on an RP system, (SrCa )SnO ( x = 0, 0.1, and 0.2), which allows for the investigation of the purely geometric (ionic size) effect on ferroelectric transitions, due to the absence of the second-order Jahn-Teller active (d and 6s) cations that often lead to ferroelectric distortions through electronic mechanisms. We observe a ferroelectric-to-paraelectric transition with T = 410 K for SrSnO. We also find that the T increases linearly up to 800 K upon increasing the Ca content, i.e., upon decreasing the value of t. Remarkably, this linear relationship is applicable to the suite of all known ABO hybrid improper ferroelectrics, indicating that the  T correlates with the simple crystal chemistry descriptor, t, based on the ionic size mismatch. This study provides a predictive guideline for estimating the T of a given material, which would complement the convergent group-theoretical and first-principles design approach

MnFe0.5Ru0.5O3: an above-room-temperature antiferromagnetic semiconductor

A transition-metal-only MnFe0.5Ru0.5O3 polycrystalline oxide was prepared by a reaction of starting materials MnO, MnO2, Fe2O3, RuO2 at 6 GPa and 1873 K for 30 minutes. A combination of X-ray and neutron powder diffraction refinements indicated that MnFe0.5Ru0.5O3 adopts the corundum (a-Fe2O3) structure type with space group R3 @#x0305;c, in which all metal ions are disordered. The centrosymmetric nature of the MnFe0.5Ru0.5O3 structure is corroborated by transmission electron microscopy, lack of optical second harmonic generation, X-ray absorption near edge spectroscopy, and Mössbauer spectroscopy. X-ray absorption near edge spectroscopy of MnFe0.5Ru0.5O3 showed the oxidation states of Mn, Fe, and Ru to be 2+/3+, 3+, and ~4+, respectively. Resistivity measurements revealed that MnFe0.5Ru0.5O3 is a semiconductor. Magnetic measurements and magnetic structure refinements indicated that MnFe0.5Ru0.5O3 orders antiferromagnetically around 400 K, with magnetic moments slightly canted away from the c axis. 57Fe Mössbauer confirmed the magnetic ordering and Fe3+ (S = 5/2) magnetic hyperfine splitting. First principles calculations are provided to understand the electronic structure more thoroughly. A comparison of synthesis and properties of MnFe0.5Ru0.5O3 and related corundum Mn2BB'O6 derivatives is discussed