A topological insulator is a state of matter which does not break any symmetry and is characterized by topological invariants, the integer expectation values of nonlocal operators. Antiferromagnetism, on the other hand, is a broken symmetry state in which the translation symmetry is reduced and time reversal symmetry is broken. Can these two phenomena coexist in the same material? A proposal by Mong et al. [Phys. Rev. B 81, 245209 (2010)] asserts that the answer is yes. Moreover, it is theoretically possible that the onset of antiferromagnetism enables the nontrivial topology since it may create spin-orbit coupling effects which are absent in the nonmagnetic phase. The current work examines a real system, half-Heusler GdBiPt, as a candidate for topological antiferromagnetism. We find that the magnetic moments of the gadolinium atoms form ferromagnetic sheets which are stacked antiferromagnetically along the body diagonal. This magnetic structure may induce spin-orbit coupling on band electrons as they hop perpendicular to the ferromagnetic sheets.

Chemical solution deposition (CSD) of YBa2Cu3O7−δ (YBCO) nanocomposites from colloidal precursor solutions containing double metal oxide preformed nanocrystals is a promising, costeffective and reproducible approach to produce superconducting films with high critical current density (Jc) and enhanced pinning. Here, the influence of the preformed nanocrystal composition on the microstructure and superconducting properties of the YBCO nanocomposite films is studied, with a focus on establishing a simple and scalable process to grow nanocomposites that can be transferred to grow nano-added coated conductors. Colloidal stable BaZrO3, BaHfO3, BaTiO3 and SrZrO3 nanocrystals (3-6 nm in diameter) were synthesized and added to an environment-friendly low-fluorine YBCO precursor solution. High-quality superconducting layers were grown on LaAlO3 single-crystal substrates from these four nanocomposite precursor solutions in a single deposition process, without the need of a seed layer, yielding Jc of 4-5 MA/cm² at 77 K in self-field. The different YBCO microstructures produced by the four types of nanocrystals and the resulting microstrain of the films are compared and related with the magnetic-field and angular dependence of Jc. We demonstrate the BaHfO3-containing nanocomposite as the best-performing with a homogeneous distribution of nanoparticles with 7 nm in average diameter and a high density of stacking faults, which leads to some of the best superconducting properties ever achieved via low-fluorine CSD. The Jc exhibits a much smoother decay in applied magnetic fields and a much more isotropic behaviour for non-parallel magnetic fields, and the pinning force is increased by a factor of 3.5 at 77 K and 1 T with respect to the pristine film.

Magnetic measurements at 4.2K, 35K and 120K are reported for iron silicate (<-Fe2SiO4 in fields up to 15 Tesla. The two nonequivalent Fe2+ ions occupy two different octahedral sites in space group Pnma. Unpolarized neutron experiments gave different and reduced magnetic moments for the colinear antiferromagnetic region (23K < T < 65K). The difference is less pronounced in the canted structure below 23K. Polarized neutron experiments in the paramagnetic region with a field of 4.6 Tesla induced a magnetic moment of 0.1µB per atom. Magnetic form factors were derived and the preliminary analysis of the data gave some indication of magnetization density between Fe2+ and oxygen atoms

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