Browsing by Author "Lee, WTH"
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- ItemMagnetic 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, BPPOur 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
- ItemMagnetization enhancement by exchange coupling of antiferromagnetic nanoparticles embedded in ferromagnetic matrix(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Ding, X; Tseng, LT; Lee, WTH; Yi, JWe have observed enhanced magnetisation as a consequence of the exchange-coupling of antiferromagnetic nanoparticle embedded in ferromagnetic matrix. Magnetic behaviour in nanostructure has been found to be significantly different from the magnetic behaviour in bulk materials. As an example, Ni cluster has a saturation moment of 2 µB compared to 0.6 µB in bulk form [1]. In our previous work, we found NiO nanoparticles to be a ferromagnet with a saturation magnetization of 105 emu/g at 5 K, corresponding to 1.16 µB/Ni [2]. It should be noted that bulk NiO is an antiferromagnet. However, the high saturation magnetization in these materials can only be observed at very low temperature. In 2003, Skumryev et. al. found that nanostructured Co had an enhanced blocking temperature when coated with antiferromagnetic CoO due to the exchange coupling between Co core and CoO surface [3]. Exchange coupling has therefore been proposed to be a mechanism that can lead to room-temperature high-magnetisation materials. To test this hypothesis, we fabricated Ni/NiO composite thin films using laser-MBE method. Magnetisation measurement using SQUID and layer-by-layer chemical and magnetic structure determination using polarized neutron reflectivity both showed that nanostructured NiO embedded in Ni matrix has led to an enhancement of room-temperature magnetisation higher than that of pure Ni films, thus providing evidence that supports the hypothesis.