W.J. Li

Exchange bias in two-step artificially grown one-dimensional hybrid Co-BiFeO3core-shell nanostructures

One-dimensional core-shell nanostructures consisting of a ferromagnetic cobalt core and a multiferroic BiFeO3 (BFO) shell were fabricated by an artificial two-step methodology. The coupling between the ferromagnetic core and multiferroic shell manifests a significant exchange bias effect which gives a clear demonstration of the anti-ferromagnetic functionality of the BFO shell material. Exchange biases of 30 Oe and 60 Oe are observed at 300 K and at 5 K, respectively. Superparamagnetic contributions at lower temperatures play an important role in contributing to overall magnetic behavior. Dominant shape anisotropy causes parallel alignment of the easy magnetization axis along the axis of core-shell nanowires. A coherent mode of the magnetization reversal mechanism is observed by the angular dependence of coercivity (H c). This versatile two-step methodology can be employed to fabricate and investigate many other hybrid nanostructures leading to a vast scope of investigation for researchers.

Enhanced exchange bias in IrMn/CoFe deposited on self-organized hexagonally patterned nanodots

Exchange biased nanostructures of IrMn/CoFe were deposited on anodized alumina with hexagonally patterned nanodot surface structures. Nanodots with diameters of 20, 70, and 100u2009nm were fabricated to investigate the size effect on the magnetic properties. Magnetometry and the first-order reversal curve method revealed significant enhancements of the exchange bias and coercivity in the nanodots compared with flat films. The enhancements can be attributed to the effective reduction of ferromagnet domain sizes and increased random fields due to the nanostructure morphology and domain wall pinning by the boundaries between adjacent nanodots.

Experimental investigation and micromagnetic simulations of hybrid CoCr2O4/Ni coaxial nanostructures

Multiphase CoCr2O4/Ni core-shell nanowires (NWs) have been synthesized within anodic aluminum oxide membranes by the combination of the sol-gel method with electrodeposition techniques. X-ray diffraction and x-ray photoemission spectroscopy results confirmed the formation of a cubic spinel structure of CoCr2O4 shell with space group Fd-3m (227). The morphology and composition of the as-grown NWs were studied by field emission scanning electron microscopy, as well as transmission electron microscopy. The magnetic properties of the CoCr2O4 NT shell and hybrid CoCr2O4/Ni NWs were measured at low temperature using a physical property measurement system. The temperature dependence of the magnetization curves showed that CoCr2O4 NTs undergo a transition from a paramagnetic state to a ferrimagnetic state at about 90 K and a spiral ordering transition temperature near 22 K. An enhanced coercivity and saturation field were observed for the CoCr2O4/Ni core-shell NWs compared to the single-phase Ni NWs. Micromagnetic simulation results indicated that there is a strong coupling between the shell and core layers during the magnetization reversal process. The combination of hard CoCr2O4 and soft Ni in a single NW structure may have potential applications in future multifunctional devices.

Wide-angle polarization-free plasmon-enhanced light absorption in perovskite films using silver nanowires

Since the successful implementation of organic-inorganic hybrid perovskites as light-absorbing materials, stunning progresses have been made towards the efficiency boost of perovskite solar cells. To build upon these successes, further impetus may derive from revisits to the intrinsic properties of perovskites, such as their optical properties. Herein, we introduce periodic Ag nanowire (AgNW) structures into perovskite films to optimize their solar absorption efficiency through plasmonic interactions. Numerical simulations show a remarkable integrated solar absorption enhancement of 25.9% attained by incorporating properly tailored AgNW arrays into perovskite films. The AgNW crosses are further introduced to achieve polarization-independent light harvesting capability. The omnidirectional light absorption enhancement ability of the AgNW embedded perovskite films is also demonstrated.

Fabrication, structural and magnetic properties of electrodeposited Fe 80 Pt 20 nanowires and nanotubes

Summary form only given. Magnetic nanostructures have attracted a great deal of attention during the last decade because of their prospective applications not only in microwave absorption, high density recording media, and biosensor applications but also in functional micro and nanodevices. Recently, significant investigations have been motivated to get excess of 1Tbit/in2 in magnetic storage devices but at smaller bit size superparamagnetic limit arises. The process of DC electrodeposition has been employed to synthesize highly ordered Fe80Pt20 nanowires (NWs) and nanotubes (NTs) in anodic aluminum oxide (AAO) templates with average pore diameter of about 200 nm. The structural and magnetic properties of nanostructures has been investigated before and after simple and magnetic field annealing. A significant influence of magnetic field annealing with field strength of 1 T has been observed in the direction parallel and perpendicular to NWs and NTs axis respectively. X-Ray Diffraction analysis showed face centered cubic (fcc) as the dominant phase for Fe80Pt20 NWs and post annealing led to better crystallinity with retained fcc phase. On the other hand, Fe80Pt20 NTs shows amorphous behavior before and after simple and magnetic field annealing. Furthermore, magnetic properties, including saturation magnetization (Ms), squareness (Mr/Ms), and coercivity (Hc), have been investigated as a function of annealing temperature by Vibrating Sample Magnetometer. In conclusion, behavior of coercivity (Hc) was based on prolate ellipsoid chain model. Microstructural and magnetic properties strongly correlate with each other.