Emma E. McCabe

Structural characterization and physical properties of the new transition metal oxyselenide La2O2ZnSe2.

The quaternary transition metal oxyselenide La(2)O(2)ZnSe(2) has been shown to adopt a ZrCuSiAs-related structure with Zn(2+) cations in a new ordered arrangement within the [ZnSe(2)](2-) layers. This cation-ordered structure can be derived and described using the symmetry-adapted distortion mode approach. La(2)O(2)ZnSe(2) is an direct gap semiconductor with an experimental optical band gap of 3.4(2) eV, consistent with electronic structure calculations.

Infinitely Adaptive Transition-Metal Ordering in Ln2O2MSe2-Type Oxychalcogenides

A number of Ln2O2MSe2 (Ln = La and Ce; M = Fe, Zn, Mn, and Cd) compounds, built from alternating layers of fluorite-like [Ln2O2](2+) sheets and antifluorite-like [MSe2](2-) sheets, have recently been reported in the literatures. The available MSe4/2 tetrahedral sites are half-occupied, and different compositions display different ordering patterns: [MSe2](2-) layers contain MSe4/2 tetrahedra that are exclusively edge-sharing (stripe-like), exclusively corner-sharing (checkerboard-like), or mixtures of both. This paper reports 60 new compositions in this family. We reveal that the transition-metal arrangement can be systematically controlled by either Ln or M doping, leading to an infinitely adaptive structural family. We show how this is achieved in La2O2Fe1-xZnxSe2, La2O2Zn1-xMnxSe2, La2O2Mn1-xCdxSe2, Ce2O2Fe1-xZnxSe2, Ce2O2Zn1-xMnxSe2, Ce2O2Mn1-xCdxSe2, La2-yCeyO2FeSe2, La2-yCeyO2ZnSe2, La2-yCeyO2MnSe2, and La2-yCeyO2CdSe2 solid solutions.

Weak spin interactions in Mott insulating La2O2Fe2OSe2

Identifying and characterizing the parent phases of iron-based superconductors is an important step towards nunderstanding the mechanism for their high-temperature superconductivity. We present an investigation into nthe magnetic interactions in the Mott insulator La2O2Fe2OSe2. This iron oxyselenide adopts a 2-k magnetic nstructure with low levels of magnetic frustration. This magnetic ground state is found to be dominated by nnext-nearest-neighbor interactions J2 and J2? and the magnetocrystalline anisotropy of the Fe2+ site, leading nto 2D-Ising-like spin S = 2 fluctuations. In contrast to calculations, the values are small and confine the spin nexcitations below ?25 meV. This is further corroborated by sum rules of neutron scattering. This indicates that nsuperconductivity in related materials may derive from a weakly coupled and unfrustrated magnetic structure.

The magnetic and electronic properties of oxyselenides-influence of transition metal ions and lanthanides.

Magnetic oxyselenides have been a topic of research for several decades, firstly in the context of photoconductivity and thermoelectricity owing to their intrinsic semiconducting properties and ability to tune the energy gap through metal ion substitution. More recently, interest in the oxyselenides has experienced a resurgence owing to the possible relation to strongly correlated phenomena given the fact that many oxyselenides share a similar structure to unconventional superconducting pnictides and chalcogenides. The two dimensional nature of many oxyselenide systems also draws an analogy to cuprate physics where a strong interplay between unconventional electronic phases and localised magnetism has been studied for several decades. It is therefore timely to review the physics of the oxyselenides in the context of the broader field of strongly correlated magnetism and electronic phenomena. Here we review the current status and progress in this area of research with the focus on the influence of lanthanides and transition metal ions on the intertwined magnetic and electronic properties of oxyselenides. The emphasis of the review is on the magnetic properties and comparisons are made with iron based pnictide and chalcogenide systems.

Crystal field excitations and magnons : their roles in oxyselenides Pr2O2M2OSe2 (M = Mn, Fe).

We present the results of neutron scattering experiments to study the crystal and magnetic structures of the Mott-insulating transition metal oxyselenides Pr2O2M2OSe2 (M = Mn, Fe). The structural role of the non-Kramers nPr3+ ion was investigated, and analysis of Pr3+ crystal field excitations was performed. Long-range order of Pr3+ nmoments in Pr2O2Fe2OSe2 can be induced by an applied magnetic field.

Magnetism of the Fe2+ and Ce3+ sublattices in Ce2O2FeSe2 : a combined neutron powder diffraction, inelastic neutron scattering, and density functional study.

The discovery of superconductivity in the 122 iron selenide materials above 30 K necessitates an understanding of the underlying magnetic interactions. We present a combined experimental and theoretical investigation of magnetic and semiconducting Ce 2 O 2 FeSe 2 composed of chains of edge-linked iron selenide tetrahedra. The combined neutron diffraction and inelastic scattering study and density functional calculations confirm the ferromagnetic nature of nearest-neighbor Fe-Se-Fe interactions in the ZrCuSiAs-related iron oxyselenide Ce 2 O 2 FeSe 2 . Inelastic measurements provide an estimate of the strength of nearest-neighbor Fe-Fe and Fe-Ce interactions. These are consistent with density functional theory calculations, which reveal that correlations in the Fe-Se sheets of Ce 2 O 2 FeSe 2 are weak. The Fe on-site repulsion U Fe is comparable to that reported for oxyarsenides and K 1−x Fe 2−y Se 2 , which are parents to iron-based superconductors.

Magnetic order and phase transition in the iron oxysulfide La2O2Fe2OS2

Abstract The Mott-insulating iron oxychalcogenides exhibit complex magnetic behaviour and we report here a neutron diffraction investigation into the magnetic ordering in La2O2Fe2OS2. This quaternary oxysulfide adopts the anti-Sr2MnO2Mn2Sb2-type structure (described by space group I4/mmm) and orders antiferromagnetically below TNxa0=xa0105xa0K. We consider both its long-range magnetic structure and its magnetic microstructure, and the onset of magnetic order. It adopts the multi-k vector “2k” magnetic structure (kxa0=xa0(1/2xa00xa01/2) and kxa0=xa0(0xa01/2xa01/2) and has similarities with related iron oxychalcogenides, illustrating the robust nature of the “2k” magnetic structure.

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 (TNu2009=u200958u2009K) 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.Double corundum-related polar magnets are promising for multiferroic and magnetoelectric applications in spintronics, but are limited by the challenging design and synthesis. Here the authors report the synthesis of Mn2MnWO6 as well as its appealing multiferroic and magnetoelectric properties.

Structural and magnetic characterization of iron oxyselenidesCe2O2Fe2OSe2andNd2O2Fe2OSe2

We present here an investigation of the magnetic ordering in the Mott insulating oxyselenide materials Ln2O2Fe2OSe2 (Ln = Ce, Nd). Neutron powder diffraction data are consistent with a non-collinear multi-k ordering on the iron sublattice structure and analysis indicates a reduced magnetic correlation length perpendicular to the [Fe2O]2+ layers. The magnetic role of the Ln3+ cations is investigated and Ce3+ moments are found to order for T < 16 K.

Structural and magnetic characterization of iron oxyselenides Ce2O2Fe2OSe2 and Nd2O2Fe2OSe2

We present here an investigation of the magnetic ordering in the Mott insulating oxyselenide materials Ln2O2Fe2OSe2 (Ln = Ce, Nd). Neutron powder diffraction data are consistent with a non-collinear multi-k ordering on the iron sublattice structure and analysis indicates a reduced magnetic correlation length perpendicular to the [Fe2O]2+ layers. The magnetic role of the Ln3+ cations is investigated and Ce3+ moments are found to order for T < 16 K.