Browsing by Author "Mallett, BPP"

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    Magnetic ordering in superconducting sandwiches
    (Australian Nuclear Science and Technology Organisation, 2021-11-24) Chan, A; van der Heijden, NJ; Causer, GL; Söhnel, T; Simpson, MC; Rule, KC; Lee, WTH; Bernhard, C; Mallett, BPP
    Our cuprate-manganite ‘superconducting sandwich’ multilayers exhibit a highly unusual magnetic-field induced insulating-to-superconducting transition (IST), contrary to the commonly held understanding that magnetic fields are detrimental to superconductivity [1, 2]. This new behaviour is a result of the specific magnetic and electronic properties of the manganite coupling with the high-Tc cuprate (YBa2Cu3O7-δ, YBCO). Due to the specific manganite composition, Nd0.65(Ca0.7Sr0.3)0.35MnO3 (NCSMO), we hypothesize the behaviour to originate from CE-type antiferromagnetic ordering as well as charge and orbital ordering [3]. The magnetic data presented here will focus on polarized neutron reflectometry (PNR) and elastic neutron scattering on a YBCO-NCSMO trilayer and superlattice. The model that best described the PNR data for the trilayer had antiparallel moments at the YBCO-NCSMO interfaces. In the superlattice, the direction of moments at NCSMO interfaces were found to alternate with film depth whose long-ranged ordering was broken below 35 K in a 1 T applied field. The stability of the AFM order in the superlattice was further supported by a robustness of magnetic in-plane half-order elastic scattering peaks at 9 T. This evidences the interplay of magnetism and superconductivity that play a role in realizing the IST effect in our superconducting sandwiches. © The Authors
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    Magnetic ordering in superconducting sandwiches
    (Australian Institute of Physics, 2020-02-04) Chan, A; van der Heijden, NJ; Söhnel, T; Simpson, MC; Rule, KC; Causer, GL; Lee, WT; Bernard, C; Mallett, BPP
    Our cuprate-manganite ‘superconducting sandwich’ multilayers exhibit a highly unusual magnetic-field induced insulating-to-superconducting transition, contrary to the commonly held understanding that magnetic fields are detrimental to superconductivity. This new behaviour is a result of the specific magnetic and electronic properties of the manganite coupling with the cuprate (YBa2Cu3O7-δ, YBCO). Due to the specific manganite composition, Nd0.65(Ca0.7Sr0.3)0.35MnO3 (NCSMO), we hypothesize the behaviour to originate from CE-type antiferromagnetic ordering as well as charge and orbital ordering. Zero-field cooled polarized neutron reflectometry (PNR) data in Fig 1(A) shows a sizable spin-flip (R+-) signal which may result from disordered ferromagnetic domains which sum to give a vanishing macroscopic magnetization. Initial elastic neutron scattering measurements performed on 100 nm thin film NCSMO display signatures of magnetic ordering (Fig 1(B)). Future neutron scattering measurements will look at the modification of magnetic order in a superlattice to better understand the relationship between NCSMO magnetization and our newly discovered insulating-to-superconducting transition.
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    Oxygen isotope effect in high temperature superconductors - phonons or magnons?
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2012-11-07) Barber, FJ; Tallon, JL; Mallett, BPP; Avdeev, M
    The oxygen isotope effect displayed in the critical temperature, Tϲ, by high temperature superconducting (HTS) cuprates was studied using polycrystalline samples of YBa2Cu3O6. The dominant perspective within the community is that this isotope effect is resultant from lattice vibrations or 'phonons'. In contrast, our treatment assesses the viability of explaining this effect by an indirectly acting magnetic mechanism. This proposed mechanism involves an increase in the anti- ferromagnetic super-exchange interaction energy, J, between adjacent Cu(2) ions as a result of decreasing unit cell basal area from a decrease in lattice vibration magnitudes. Polycrystalline YBa2Cu3O6 samples of similar mass were synthesised under identical conditions, then co-annealed under 16O and 18O gas respectively. Neutron diffraction experiments were performed on these samples at 3K, 50K and 100K to accurately determine structural parameters. Rietveld refinement produced inferred critical temperature isotope exponents, α = of α-(3K)=(3.6±0.4)x103, α(50K)=(4.3±0.6)x103, and α (100K)=(7.2±0.9)x103. Comparison with the experimentally measured isotope effect of α=0.06 in the overdoped region indicates that our mechanism is unlikely to be sufficient to account for the isotope effect in Tϲ. We note, however, that there remains a possibility of a secondary contribution from this mechanism. This project plans for further back-exchange and repeated diffraction measurements, which will aid in confirming and comparing these results.