Muons and magnets

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Microscopic effects of Dy-doping in the topological insulator Bi2Te3

(2018)

Authors:

LB Duffy, N-J Steinke, JA Krieger, AI Figueroa, K Kummer, T Lancaster, SR Giblin, FL Pratt, SJ Blundell, T Prokscha, A Suter, S Langridge, VN Strocov, Z Salman, G van der Laan, T Hesjedal

Evidence for $J_{\rm eff} = 0$ ground state and defect-induced spin glass behaviour in the pyrochlore osmate Y$_{2}$Os$_{2}$O$_{7}$

(2018)

Authors:

NR Davies, CV Topping, H Jacobsen, AJ Princep, FKK Kirschner, MC Rahn, M Bristow, JG Vale, I da Silva, PJ Baker, Ch J Sahle, Y-F Guo, D-Y Yan, Y-G Shi, SJ Blundell, DF McMorrow, AT Boothroyd

Spin Jahn-Teller antiferromagnetism in CoTi$_2$O$_5$

(2018)

Authors:

Franziska KK Kirschner, Roger D Johnson, Franz Lang, Dmitry D Khalyavin, Pascal Manuel, Tom Lancaster, Dharmalingam Prabhakaran, Stephen J Blundell

Doped Sr2FeIrO6-Phase Separation and a Jeff ≠ 0 State for Ir5.

Inorganic chemistry 57:16 (2018) 10303-10311

Authors:

Jacob E Page, Craig V Topping, Alex Scrimshire, Paul A Bingham, Stephen J Blundell, Michael A Hayward

Abstract:

High-resolution synchrotron X-ray and neutron powder diffraction data demonstrate that, in contrast to recent reports, Sr2FeIrO6 adopts an I1̅ symmetry double perovskite structure with an a-b-c- tilting distortion. This distorted structure does not tolerate cation substitution, with low levels of A-site (Ca, Ba, La) or Fe-site (Ga) substitution leading to separation into two phases: a stoichiometric I1̅ phase and a cation-substituted, P21/ n symmetry, a-a-c+ distorted double perovskite phase. Magnetization, neutron diffraction, and 57Fe Mössbauer data show that, in common with Sr2FeIrO6, the cation substituted Sr2- xA xFe1- yGa yIrO6 phases undergo transitions to type-II antiferromagnetically ordered states at TN ∼ 120 K. However, in contrast to stoichiometric Sr2FeIrO6, cation substituted samples exhibit a further magnetic transition at TA ∼ 220 K, which corresponds to the ordering of Jeff ≠ 0 Ir5+ centers in the cation-substituted, P21/ n symmetry, double perovskite phases.

Ultra-high critical current densities, the vortex phase diagram and the effect of granularity of the stoichiometric high-Tc superconductor, CaKFe4As4

Physical Review Materials American Physical Society 2:2018 (2018) 074802

Authors:

Shiv Singh, Matthew Bristow, WR Meier, Patrick Taylor, Stephen Blundell, PC Canfield, Amalia Coldea

Abstract:

We present a comprehensive study of the critical current densities and the superconducting vortex phase diagram in the stoichiometric superconductor CaKFe4As4 which has a critical temperature of ∼35 K. We performed detailed magnetization measurements both of high quality single crystals for different orientations in an applied magnetic field up to 16 T and for a powder sample. We find an extremely large critical current density, Jc, up to 108 A/cm2 for single crystals when H(ab) at 5 K, which remains robust in fields up to 16 T, being the largest of any other iron-based superconductor. The critical current density is reduced by a factor 10 in single crystals when Hc at 5 K and significantly suppressed by the presence of grain boundaries in the powder sample. We also observe the presence of the fishtail effect in the magnetic hysteresis loops of single crystals when Hc. The flux pinning force density and the pinning parameters suggest that the large critical current could be linked to the existence of point core and surface pinning. Based on the vortex phase diagram and the large critical current densities, CaKFe4As4 is now established as a potential iron-based superconductor candidate for practical applications.