The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202207152. Magnetic materials with the spinel structure (A 2+ B 3+2 O 4 ) form the core of numerous magnetic devices, and ZnFe 2 O 4 constitutes a peculiar example where the nature of the magnetism is still unresolved. Susceptibility measurements revealed a cusp around T c = 13 K resembling an antiferromagnetic transition, despite the positive Curie-Weiss temperature determined to be Θ CW = 102.8(1) K. Bifurcation of field-cooled and zero-field-cooled data below T c in conjunction with a frequency dependence of the peak position and a non-zero imaginary component below T c shows it is in fact associated with a spin-glass transition. Highly structured magnetic diffuse neutron scattering from single crystals develops between 50 K and 25 K revealing the presence of magnetic disorder which is correlated in nature. Here, the 3D-mΔPDF method is used to visualize the local magnetic ordering preferences, and ferromagnetic nearest-neighbor and antiferromagnetic third nearest-neighbor correlations are shown to be dominant. Their temperature dependence is extraordinary with some flipping in sign and a strongly varying correlation length. The correlations can be explained by orbital interaction mechanisms for the magnetic pathways and a preferred spin cluster. This study demonstrates the power of the 3D-mΔPDF method in visualizing complex quantum phenomena thereby providing a way to obtain an atomic-scale understanding of magnetic frustration.

An important frontier in materials science is to understand, characterize and quantize disorder in inorganic materials and its relation to their properties. This requires deep knowledge of both the average structure and the defects present in the samples. Spinel-type compounds form a family of industrially relevant materials1 that potentially exhibit both atomic and/or magnetic disorder.2, 3 Spinel ferrites, AFe2O4, in particular have seen use in high-frequency applications due to their magnetism in conjunction with electrically insulating properties. The spinel structure consists of a distorted cubic closest packing of oxygen, in which 1/8 of the tetrahedral holes and 1/2 of the octahedral holes are occupied by cations. The general formula is AB2O4, where A are divalent and B trivalent cations.Single crystals larger than 1 mm3 of ZnFe2O4 and NiFe2O4 have been grown using the flux method. These were chosen as model spinel ferrites exhibiting the normal and inverse configuration, respectively, with the possibility of magnetic disorder studies in ZnFe2O4.4 X-ray fluorescence measurements confirmed a low degree of flux inclusions in the crystals, on the order of 0.1 wt%.Extensive diffraction data has been collected for initial benchmark structure determination, with synchrotron powder X-ray diffraction and single crystal X-ray diffraction being collected at SPring-8 in Japan, and single crystal neutron diffraction being collected at the Spallation Neutron Source at Oak Ridge National Laboratory. Initial data modelling shows some systematic discrepancies between the structural parameters obtained from the different sets of diffraction data. Rietveld modelling of the powder data gives lower lattice parameters than either single crystal method, which has been attributed to abnormal peak asymmetry caused by a nonsymmetric X-ray beam profile. The atomic displacement parameters obtained from the X-ray single crystal and powder data of ZnFe2O4 differs both in magnitude and temperature dependence, the cause of which has not been identified yet.The powder patterns of NiFe2O4 reveal left shoulders at reflections with miller indices that are all multiples of four, which could be related to the compound's magnetism.The single crystal data show peak splitting indicating a degree of twinning on both spinel samples. Maximum entropy method analysis of the structure factors from the single crystal X-ray data showed no evidence of residual electron density at potential interstitial sites in the structure.

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Thermoelectric materials allow for conversion of waste heat into electrical energy, and they represent a green solution for improving our energy efficiency. Inclusion of 4f electrons near the Fermi level may boost the Seebeck coefficient, which is essential for high thermoelectric performance. In this study, Ce was successfully substituted for Ba on the guest atom sites in the type-I clathrate Ba8–x Ce x Au y Si46–y and the material was characterized using high-resolution synchrotron powder X-ray diffraction data measured from 100 K to 1000 K to investigate potential structural implications of the inclusion of a 4f element. The thermal expansion and bonding of the host structure are not affected by the presence of Ce, as seen from the linear coefficient of unit-cell thermal expansion of 7.30 (8) × 10−6 K−1 and the average host Debye temperature of 404 (7) K determined from the multi-temperature atomic displacement parameters, both of which are similar to values obtained for pure Ba8Au y Si46–y . The anisotropic atomic displacement parameters on the guest atom site in the large clathrate cage populated by Ba surprisingly reveals isotropic behavior, which is different from all other clathrates reported in literature, and thus represents a unique host–guest bonding situation.