Francoise Damay

Magnetic-rare-earth pyrochlore iridates exhibit a rich variety of unconventional phases, driven by the complex interactions within and between the rare-earth and the iridium sublattices. In this study, we investigate the peculiar magnetic state of Tb 2 Ir 2 O 7 , where a component of the Tb 3 + moment orders perpendicular to its local Ising anisotropy axis. By means of neutron diffraction and inelastic neutron scattering down to dilution temperatures, complemented by specific heat measurements, we show that this intriguing magnetic state is fully established at 1.5 K and we characterize its excitation spectrum across a broad range of energies. Our calculations reveal that bilinear interactions between Tb 3 + ions subjected to the Ir molecular field capture several key features of the experiments, but need to be supplemented to fully reproduce the observed behavior.

Combining macroscopic measurements, neutron scattering, and modeling, we identify in the GeFe_{2}O_{4} spinel a correlated paramagnetic state resulting from the predominance of third-neighbor antiferromagnetic interactions. These interactions materialize four interlaced families of triangular planes with 120° spins emerging from the underlying pyrochlore lattice. At lower temperatures, a phase transition occurs to a noncoplanar spin structure that is characterized by six propagation vectors. This unusual multi-q order is triggered by the presence of weaker interactions up to the sixth neighbors. The system is remarkably successful in coupling the different triangular planes while maintaining their two-dimensional 120° order. Our Letter highlights the hierarchy of interactions involved in GeFe_{2}O_{4}, which is singular among spinel compounds since first-neighbor interactions are only a small fraction of the dominant third-neighbor ones.

A few real case examples are presented on how to report magnetic structures, with precise step-by-step explanations, following the guidelines of the IUCr Commission on Magnetic Structures [Perez-Mato et al. (2024). Acta Cryst. B80, 219–234]. Four examples have been chosen, illustrating different types of single-k magnetic orders, from the basic case to more complex ones, including odd-harmonics, and one multi-k order. In addition to acquainting researchers with the process of communicating commensurate magnetic structures, these examples also aim to clarify important concepts, which are used throughout the guidelines, such as the transformation to a standard setting of a magnetic space group.

The Ca₂MnReO₆ double perovskite is a spin–orbit-assisted Mott insulator with exotic magnetic properties, including a largely non-collinear Mn²⁺ spin arrangement and nearly orthogonal coupling between such spins and the much smaller Re 5d magnetic moments. Here, the electron-doped compound Ca_1−x Y _x MnReO₆ (x = 0.1, 0.2 and 0.3) is reported and a detailed investigation is conducted for x = 0.3. Neutron and x-ray powder diffraction confirm that nearly full chemical order is maintained at the Mn and Re sites under the Y substitution at the Ca site. X-ray absorption measurements and an analysis of the Mn–O/Re–O bond distances show that the Mn oxidation state remains stable at +2 whereas Re is reduced upon doping. The electron doping increases the magnetic ordering temperature from T _c = 121 to 150 K and also enhances significantly the ferromagnetic component of the Mn spins at the expense of the antiferromagnetic component at the base temperature (T = 3 K). The lattice parameter anomalies at T _c observed in the parent compound are suppressed by the electron doping. The possible reasons for the enhanced magnetism and the suppressed magnetoelastic coupling in Ca_1.7Y_0.3MnReO₆ are discussed.