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  1. Here, we report on the low-temperature magnetic properties of the DyScO3 perovskite, which were characterized by means of single crystal and powder neutron scattering, and by magnetization measurements. Below T N = 3.15 K, Dy 3+ moments form an antiferromagnetic structure with an easy axis of magnetization lying in the ab plane. The magnetic moments are inclined at an angle of ~ ±28° to the b axis. We show that the ground-state Kramers doublet of Dy 3+ is made up of primarily |±15/2> eigenvectors and well separated by a crystal field from the first excited state at E 1 =more » 24.9 meV. This leads to an extreme Ising single-ion anisotropy, M /M ~0.05. The transverse magnetic fluctuations, which are proportional to M 2 /M 2 , are suppressed, and only moment fluctuations along the local Ising direction are allowed. We also found that the Dy-Dy dipolar interactions along the crystallographic c axis are two to four times larger than in-plane interactions.« less
  2. Quantum materials such as antiferromagnets or superconductors are complex in that chemical, electronic, and spin phenomena at atomic scales can manifest in their collective properties. Although there are some clues for designing such materials, they remain mainly unpredictable. In this work, we find that enhancement of transition temperatures in BaFe 2As 2-based crystals are caused by removing local-lattice strain and electronic-structure disorder by thermal annealing. While annealing improves Neel-ordering temperature in BaFe 2As 2 crystal (T N=132K to 136K) by improving in-plane electronic defects and reducing overall a-lattice parameter, it increases superconducting-ordering temperature in optimally cobalt-doped BaFe 2As 2 crystalmore » (T c=23 to 25K) by precipitating-out the cobalt dopants and giving larger overall a-lattice parameter. And while annealing improves local chemical and electronic uniformity resulting in higher T N in the parent, it also promotes nanoscale phase separation in the superconductor resulting in lower disparity and strong superconducting band gaps in the dominant crystal regions, which lead to both higher overall T c and critical-current-density, J c« less
  3. Combined scanning tunneling microscopy, spectroscopy, and local barrier height (LBH) studies show that low-temperature-cleaved optimally doped Ba(Fe 1–xCo x) 2As 2 crystals with x = 0.06, with T c = 22 K, have complicated morphologies. Although the cleavage surface and hence the morphologies are variable, the superconducting gap maps show the same gap widths and nanometer size inhomogeneities irrelevant to the morphology. Based on the spectroscopy and LBH maps, the bright patches and dark stripes in the morphologies are identified as Ba- and As-dominated surface terminations, respectively. Magnetic impurities, possibly due to Co or Fe atoms, are believed to createmore » local in-gap state and, in addition, suppress the superconducting coherence peaks. Lastly, this study will clarify the confusion on the cleavage surface terminations of the Fe-based superconductors and its relation with the electronic structures.« less
  4. Fe 3GeTe 2 is known as an air-stable layered metal with itinerant ferromagnetism with a transition temperature of about 220 K. From extensive dc and ac magnetic measurements, we have determined that the ferromagnetic layers of Fe 3GeTe 2 order antiferromagnetically along the c-axis blow 152 K. The antiferromagnetic state was further substantiated by theoretical calculation to be the ground state. A magnetic structure model was proposed to describe the antiferromagnetic ground state as well as competition between antiferromagnetic and ferromagnetic states. Furthermore, Fe 3GeTe 2 shares many common features with pnictide superconductors and may be a promising system inmore » which to search for unconventional superconductivity.« less

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