Controlling inversion disorder in a stoichiometric spinel magnet.

In the study of frustrated quantum magnets, it is essential to be able to control the nature and degree of site disorder during the growth process, as many measurement techniques are incapable of distinguishing between site disorder and frustration-induced spin disorder. Pyrochlore-structured spinel oxides can serve as model systems of geometrically frustrated three-dimensional quantum magnets; however, the nature of the magnetism in one well-studied spinel, ZnFeO, remains unclear. Here, we demonstrate simultaneous control of both stoichiometry and inversion disorder in the growth of ZnFeO single crystals, directly yielding a revised understanding of both the collective spin behavior and lattice symmetry.

Na Bi Os O : A Diamagnetic Oxide Featuring a Pronouncedly Jahn-Teller-Compressed Octahedral Coordination of Osmium(VI).

The Jahn-Teller (JT) theorem constitutes one of the most fundamental concepts in chemistry. In transition-element chemistry, the 3d and 3d configurations in octahedral complexes are particularly illustrative, where a distortion in local geometry is associated with a reduction of the electronic energy. However, there has been a lasting debate about the fact that the octahedra are found to exclusively elongate.

Orbital Effects in Solids: Basics, Recent Progress, and Opportunities.

The properties of transition metal compounds are largely determined by nontrivial interplay of different degrees of freedom: charge, spin, lattice, and also orbital ones. Especially rich and interesting effects occur in systems with orbital degeneracy. For example, they result in the famous Jahn-Teller effect, leading to a plethora of consequences for static and dynamic properties, including nontrivial quantum effects.

Old puzzle of incommensurate crystal structure of calaverite AuTe and predicted stability of novel AuTe compound.

Gold is a very inert element, which forms relatively few compounds. Among them is a unique material-mineral calaverite, [Formula: see text] Besides being the only compound in nature from which one can extract gold on an industrial scale, it is a rare example of a natural mineral with incommensurate crystal structure. Moreover, it is one of few systems based on Au, which become superconducting (at elevated pressure or doped by Pd and Pt).

Unexpected 3+ valence of iron in FeO, a geologically important material lying "in between" oxides and peroxides.

Recent discovery of the pyrite FeO, which can be an important ingredient of the Earth's lower mantle and which in particular may serve as an extra source of water in the Earth's interior, opens new perspectives for geophysics and geochemistry, but this is also an extremely interesting material from physical point of view. We found that in contrast to naive expectations Fe is nearly 3+ in this material, which strongly affects its magnetic properties and makes it qualitatively different from well known sulfide analogue - FeS. Doping, which is most likely to occur in the Earth's mantle, makes FeO much more magnetic.

Covalent bonds against magnetism in transition metal compounds.

Magnetism in transition metal compounds is usually considered starting from a description of isolated ions, as exact as possible, and treating their (exchange) interaction at a later stage. We show that this standard approach may break down in many cases, especially in 4d and 5d compounds. We argue that there is an important intersite effect-an orbital-selective formation of covalent metal-metal bonds that leads to an "exclusion" of corresponding electrons from the magnetic subsystem, and thus strongly affects magnetic properties of the system.

Valence states and possible charge ordering in LaCo(1-x)Rh(x)O₃.

An unusual effect was discovered in Li et al (2010 J. Solid State Chem. 183 1388): the substitution of nonmagnetic low-spin Co(3+) in LaCoO3 by the formally isoelectronic and also nonmagnetic Rh(3+) led, surprisingly, to a rapid appearance of magnetism in LaCo(1-x)Rh(x)O3, even for small amounts of doping.

Metal-insulator transition and orbital order in PbRuO3.

Anomalous low temperature electronic and structural behavior has been discovered in PbRuO3. The structure [space group Pnma, a=5.563 14(1), b=7.

Bond- versus site-centred ordering and possible ferroelectricity in manganites.

Transition metal oxides with a perovskite-type structure constitute a large group of compounds with interesting properties. Among them are materials such as the prototypical ferroelectric system BaTiO(3), colossal magnetoresistance manganites and the high-T(c) superconductors. Hundreds of these compounds are magnetic, and hundreds of others are ferroelectric, but these properties very seldom coexist.