Octahedral distortion
in ABO3 perovskite materials is
ubiquitous because of the ionic size mismatch between A and B cations,
leading to various kinds of crystal symmetry. However, such a distortion
always results in centrosymmetric structures except for the covalent
bond formation because of the second-order Jahn–Teller (SOJT)
effect that occurs with d0 or lone-pair cations. Here,
we report that an unusual combination of the layered A-site cation
ordering and B-site rock salt ordering in NaYNiWO6 prepared
under high-pressure and high-temperature conditions results not only
in a polar (P21) structure, as revealed
by the neutron diffraction analysis, but exhibits multiferroic properties
below the magnetic ordering of Ni2+ ions (T
N = 21 K). Analysis of the neutron diffraction data at
20 K reveals an incommensurate sinusoidal spin ordering with the propagation
vector, k
i = (0.471(2), 0, 0.491(4)),
and a commensurate collinear spin structure with k
c = (0.5, 0, 0.5) below 18 K. X-ray diffraction data confirm
the polar structure in Dy, Ho, and Yb compounds. All four compounds
exhibit a switchable change in electric polarization (ΔP) at the magnetic ordering temperatures, demonstrating
coupling between ferroelectricity and magnetism.
The incommensurate magnetic structure
(0.47, 0, 0.49) of NaYNiWO6 exhibits unconventional spin-density
waves (SDWs) along the
[100] direction, in which up and down spins alternate in each half-wave.
This is in contrast to conventional SDWs, in which only one type of
spin is present in each half-wave. We probed the formation of these
unconventional SDWs by evaluating the spin exchanges of NaYNiWO6 based on density functional theory calculations and analyzing
the nature of the spin frustration in NaYNiWO6 and by noting
that a SDW is a superposition of two cycloids of opposite chirality.
The unconventional SDWs along the [100] direction originate from the
spin-frustrated antiferromagnetic chains of Ni2+ ions along
that direction, leading to conventional SDWs along the [101] direction
and unconventional SDWs along the [001] direction.
We report the structural, magnetic,
and electrical properties of
a new family of doubly ordered perovskites NaLnNiWO6 (Ln
= La, Pr, Nd, Sm, Eu, Gd, and Tb), synthesized at high-pressure (4.5
GPa) and high-temperature (1000 °C) conditions. These materials
crystallize in the monoclinic structure with the polar space group P21 as revealed by neutron diffraction (Ln =
La), X-ray diffraction, and second-harmonic-generation (SHG) studies.
These compounds exhibit a combined layered ordering of A-site cations
and rock-salt ordering of B-site cations with octahedral tilting,
which breaks the inversion symmetry and results in a polar structure.
The magnetic and heat capacity measurements reveal the antiferromagnetic
order of Ni2+ ion moments in the temperature range of 23–30
K, depending on the Ln ion. Analysis of neutron powder diffraction
data for the La compound reveals that the Ni2+ spins couple
antiferromagnetically along the a- and c-directions and ferromagnetically along the b-axis,
consistent with the propagation vector, k = (1/2,
0, 1/2). In contrast to the compounds with smaller lanthanide ions
(Ln = Y, Dy, Ho, and Yb), these compounds do not exhibit measurable
electric polarization at T
N but show a
dielectric anomaly.
We report a detailed study of superconductivity in polycrystalline SnTaS2 using electrical transport, magnetization and heat capacity measurements. SnTaS2 crystallizes in centrosymmetric hexagonal structure with space group P63/mmc. Electrical resistivity, magnetization and specific heat data suggest SnTaS2 to be a weakly coupled, type-II superconductor with Tc
≈ 2.8 K. First-principles calculations show signature for nodal line topology in the electronic band structure, protected by the spatial-inversion and time-reversal symmetries, that strongly gapped out by the inclusion of spin-orbit coupling (SOC). Superconductivity in layered SnTaS2 with nodal line topological state makes it a strong candidate to be considered for a 3D topological superconductor.
We report the multiferroic properties of doubly ordered perovskites NaLnCoWO 6 (Ln = Er, Tm, Yb, and Lu) and NaLuMnWO 6 synthesized under high-pressure (4.5 GPa) and high-temperature (1000 °C) conditions. Analysis of the powder Xray diffraction data reveals that these compounds crystallize in the polar monoclinic (P2 1 ) structure. These compounds are derived from the ABO 3 perovskite structure, where A-site cations (Na and Ln) exhibit layer ordering and B-site ions (M = Co or Mn and W) undergo commonly observed rock-salt ordering accompanied by a − a − c + octahedral tilting. All these materials, characterized by magnetic and dielectric measurements, reveal antiferromagnetic ordering (T N ∼ 6−8 K) accompanied by a dielectric anomaly. Furthermore, pyroelectrical current measurements show a nonswitchable polarization below T N for NaLnCoWO 6 (Ln = Er, Tm, and Yb) and NaLuMnWO 6 . In contrast, the polarization can be switched in NaLuCoWO 6 by changing the direction of the electric field (E) indicating the ferroelectric nature of this compound. The appearance of polarization below the magnetic ordering temperature (T N ) confirmed the magnetoelectric coupling of these compounds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.