Percolation-Induced Ferrimagnetism from Vacancy Order in [Gua]MnFe(HCOO) Hybrid Perovskites.

We report the magnetic behavior of the hybrid perovskites [Gua]MnFe□(HCOO) (0 ≤ ≤ 0.88), showing that vacancy ordering drives bulk ferrimagnetism for > 0.6.

Interplay of thermal diffuse scattering and correlated compositional disorder in KClBr.

Single-crystal X-ray diffuse scattering measurements are reported of the compositional series KClBr, a model system for the broader family of disordered rocksalts. Using a combination of Monte Carlo simulations and lattice dynamical calculations, we show that the observed diffuse scattering is well described in terms of (i) non-statistical anion distributions, (ii) local lattice relaxations accompanying Cl/Br substitution, and (iii) the contribution from low-energy phonons. It is found that a tendency for compositional domain formation broadens the thermal diffuse scattering by splitting and softening the acoustic phonon branches.

Geometric Frustration on the Trillium Lattice in a Magnetic Metal-Organic Framework.

In the dense metal-organic framework Na[Mn(HCOO)_{3}], Mn^{2+} ions (S=5/2) occupy the nodes of a "trillium" net. We show that the system is strongly magnetically frustrated: the Néel transition is suppressed well below the characteristic magnetic interaction strength; short-range magnetic order persists far above the Néel temperature; and the magnetic susceptibility exhibits a pseudo-plateau at 1/3-saturation magnetization. A simple model of nearest-neighbor Heisenberg antiferromagnetic and dipolar interactions accounts quantitatively for all observations, including an unusual 2-k magnetic ground state.

Efficient fitting of single-crystal diffuse scattering in interaction space: a mean-field approach.

The diffraction patterns of crystalline materials with strongly correlated disorder are characterized by the presence of structured diffuse scattering. Conventional analysis approaches generally seek to interpret this scattering either atomistically or in terms of pairwise (Warren-Cowley) correlation parameters. Here it is demonstrated how a mean-field methodology allows efficient fitting of diffuse scattering directly in terms of a microscopic interaction model.

Ferroic multipolar order and disorder in cyanoelpasolite molecular perovskites.

We use a combination of variable-temperature high-resolution synchrotron X-ray powder diffraction measurements and Monte Carlo simulations to characterize the evolution of two different types of ferroic multipolar order in a series of cyanoelpasolite molecular perovskites. We show that ferroquadrupolar order in [CNH]Rb[Co(CN)] is a first-order process that is well described by a four-state Potts model on the simple cubic lattice. Likewise, ferrooctupolar order in [NMe]B[Co(CN)] (B = K, Rb, Cs) also emerges via a first-order transition that now corresponds to a six-state Potts model.