Insights from angle-resolved photoemission spectroscopy on the metallic states of YbB6(001): E(k) dispersion, temporal changes, and spatial variation Frantzeskakis, E.; de Jong, N.; Zhang, J.X.; Zhang, X.; Li, Z.; Liang, C.L.; Wang, Y.; Varykhalov, A.; Huang, Y.; Golden, M.S. Published in:Physical Review B DOI:10.1103/PhysRevB.90.235116 Link to publicationCitation for published version (APA): Frantzeskakis, E., de Jong, N., Zhang, J. X., Zhang, X., Li, Z., Liang, C. L., ... Golden, M. S. (2014). Insights from angle-resolved photoemission spectroscopy on the metallic states of YbB6(001): E(k) dispersion, temporal changes, and spatial variation. Physical Review B, 90(23), 235116. https://doi.org/10.1103/PhysRevB.90.235116 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We report high-resolution angle-resolved photoelectron spectroscopy (ARPES) results on the (001) cleavage surface of YbB 6 , a rare-earth compound that has been recently predicted to host surface electronic states with topological character. We observe two types of well-resolved metallic states, whose Fermi contours encircle the time-reversal invariant momenta of the YbB 6 (001) surface Brillouin zone, and whose full E(k) dispersion relation can be measured wholly unmasked by states from the rest of the electronic structure. Although the two-dimensional character of these metallic states is confirmed by their lack of out-of-plane dispersion, our work reveals two aspects which were not observed in previous experiments. First, these states do not resemble two branches of opposite, linear velocity that cross at a Dirac point, but rather straightforward parabolas that terminate to high binding energy with a clear band bottom. Secondly, these states are sensitive to time-dependent changes of the YbB 6 surface under ultrahigh-vacuum conditions. Adding the fact that these data from cleaved YbB 6 surfaces also display spatial variations in the electronic structure, it appears there is little in common between the theoretical expectations for an idealized YbB 6 (001) crystal truncation on the one hand, and these ARPES data from real cleavage surfaces on the other.

Magnetocaloric materials can be useful in magnetic refrigeration applications, but to be practical the magneto-refrigerant needs to have a very large magnetocaloric effect (MCE) near room temperature for modest applied fields (<2 Tesla) with small hysteresis and magnetostriction, and should have a complete magnetic transition, be inexpensive, and environmentally friendly. One system that may fulfill these requirements is Mn x Fe 2-x P 1-y Ge y , where a combined first-order structural and magnetic transition occurs between the high temperature paramagnetic and low temperature ferromagnetic phase. We have used neutron diffraction, differential scanning calorimetry, and magnetization measurements to study the effects of Mn and Ge location in the structure on the ordered magnetic moment, MCE, and hysteresis for a series of compositions of the system near optimal doping. The diffraction results indicate that the Mn ions located on the 3f site enhance the desirable properties, while those located on the 3g sites are detrimental. The entropy changes measured directly by calorimetry can exceed 40 J/kg·K. The phase fraction that transforms, hysteresis of the transition, and entropy change can be controlled by both the compositional homogeneity and the particle size, and an annealing procedure has been developed that substantially improves the performance of all three properties of the material. On the basis of these results we have identified a pathway to optimize the MCE properties of this system for magnetic refrigeration applications.

Spark plasma sintering technique had been applied to prepare bulk isotropic and anisotropic nanostructured Nd–Fe–B permanent magnets via hot pressing and subsequent hot deformation process. Influences of processing conditions and deformation height reduction on the structure and magnetic properties of the magnets were investigated. For the hot deformed magnet with 80% height reduction, XRD patterns of the anisotropic magnets show dominant (00l) diffraction peaks indicating evident c-axis crystallographic alignment in the magnet. Under the optimal processing conditions, the anisotropic magnet with 80% height reduction exhibits excellent magnetic properties as remanence (Br) of 1.492 T, coercive force (Hci) of 1004 kA/m, and the maximum energy product [(BH)max] of 400 kJ/m3, which are among the highest reported magnetic properties of nanostructured Nd–Fe–B permanent magnets.

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