Jiunn-Yuan Lin

Synthesis of Epitaxial Metal Oxide Nanocrystals via a Phase Separation Approach

Perovskite phase instability of BiMnO3 has been exploited to synthesize epitaxial metal oxide magnetic nanocrystals. Thin film processing conditions are tuned to promote the breakdown of the perovskite precursor into Bi2O3 matrix and magnetic manganese oxide islands. Subsequent cooling in vacuum ensures complete volatization of the Bi2O3, thus leaving behind an array of self-assembled magnetic Mn3O4 nanostructures. Both shape and size can be systematically controlled by the ambient oxygen environments and deposition time. As such, this approach can be extended to any other Bi-based complex ternary oxide system as it primarily hinges on the breakdown of parent Bi-based precursor and subsequent Bi2O3 volatization.

Large Magnetoresistance in Magnetically Coupled SrRuO3 –CoFe2O4 Self-Assembled Nanostructures

A new way to induce a large magnetoresistance has been achieved by self-assembled nanostructures consisting of ferromagnetic spinel CoFe₂O₄ (CFO) and metallic perovskite SrRuO₃ (SRO). The interdiffused Fe³⁺ ions in SRO have paved the way to strong magnetic couplings with CFO nanopillars, resulting in the suppression of spin-polarized electron scattering.

Thickness dependence of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 magnetoelectric interfaces

Magnetoelectric materials have great potential to revolutionize electronic devices due to the coupling of their electric and magnetic properties. Thickness varying La0.7Sr0.3MnO3 (LSMO)/PbZr0.2Ti0.8O3 (PZT) heterostructures were built and measured in this article by valence sensitive x-ray absorption spectroscopy. The sizing effects of the heterostructures on the LSMO/PZT magnetoelectric interfaces were investigated through the behavior of Mn valence, a property associated with the LSMO magnetization. We found that Mn valence increases with both LSMO and PZT thickness. Piezoresponse force microscopy revealed a transition from monodomain to polydomain structure along the PZT thickness gradient. The ferroelectric surface charge may change with domain structure and its effects on Mn valence were simulated using a two-orbital double-exchange model. The screening of ferroelectric surface charge increases the electron charges in the interface region, and greatly changes the interfacial Mn valence, which likely ...

Crossover between superconductivity and magnetism in SrRuO3 mesocrystal embedded YBa2Cu3O7−x heterostructures

The competition between superconductivity and ferromagnetism poses great challenges and has attracted renewed interest for applications in novel spintronic devices. In order to emphasize their interactions, we fabricated a heterostructure composed of superconducting YBa2Cu3O7-δ (YBCO) film embedded with itinerant ferromagnetic SrRuO3 (SRO) mesocrystals. Starting from a doping concentration of 10 vol% of SRO mesocrystal in a YBCO matrix, corresponding to the density of SRO nanocrystals ∼5 × 109 cm-2, which exhibits the typical characteristic of a metal-superconductor transition, and then increasing the magnetic interactions as a function of SRO embedment, the electronic correlation and the interplay between superconductivity and magnetism throughout the temperature regime were investigated. A metal-insulator transition in the normal state of YBCO and a crossover between superconductivity and magnetism at low temperatures were found upon increasing the density of nano-size SRO crystallites in the YBCO matrix as a consequence of competing interactions between these two ordered phases.

Negative and positive electroluminescence from a compensated p-type germanium in terahertz frequencies

Negative luminescence (NL) and positive luminescence in terahertz frequencies were observed from a compensated p-type Ge under various levels of pulse excitations at cryogenic temperatures. The NL spectra accompanying an S-type negative differential resistance phenomenon were attributed to the reduced emission transitions from the excited states to the ground states of the acceptors during the excitation. A possible excitation mechanism is also presented according to the measured data.