Yupei Wang

Low temperature growth of vanadium pentoxide nanomaterials by chemical vapour deposition using VO(acac)2 as precursor

Vanadium pentoxide (V2O5) nanomaterials with various morphologies were prepared by chemical vapour deposition at a relatively low temperature (evaporation temperature of 250u2009°C and growth temperature of 500u2009°C) using vanadyl acetylacetonate (VO(acac)2) powder as the vanadium precursor. The obtained samples were characterized by scanning electron microscopy, x-ray diffraction, Raman scattering and photoluminescence spectra. The results revealed that the samples including a V2O5 nanocluster film, V2O5 nanowires and V2O5 nanospheres were synthesized at different distances from the source material. For our chemical vapour transport system, we suggested that VOx vapour and VO(acac)2 vapour existed simultaneously during the growth process, which resulted in different morphologies of V2O5 nanomaterials. The quite different supersaturation distributions of VOx vapour and VO(acac)2 vapour led to three main growth areas. The V2O5 film was grown in the region where the supersaturation of the VOx vapour was high, V2O5 nanowires were obtained where the supersaturation of the VOx vapour was relatively low and V2O5 nanospheres were synthesized in the region where the supersaturation of the VO(acac)2 vapour was high. The growth pressure that influenced the vapour concentration controlled the morphologies of the nanowires. It was found that a specific level of low concentration was necessary to ensure the growth of V2O5 nanowires.

Current-induced magnetization switching in Pt/Co/Ta with interfacial decoration by insertion of Cr to enhance perpendicular magnetic anisotropy and spin–orbit torques

Perpendicular magnetic anisotropy (PMA) and spin–orbit torques (SOTs) are studied in a perpendicularly magnetized ultrathin Co film sandwiched between heavy metal Pt and Ta with an interfacial decoration performed by inserting a 3d transition metal Cr layer with a thickness of 2 nm between the Co and Ta. A significant enhancement of the perpendicular anisotropy field ( Oe) is established and estimated by measuring the extraordinary Hall resistance due to the Cr interfacial decoration. The improved antidamping-like field of ~18.59 × 10−6 Oe/(Acm−2) reveals a large effective spin Hall angle of Pt/Co/Cr/Ta ~0.41, which is caused by employing the dissimilar metals, Pt and Ta, with spin Hall angles of opposite sign and an additional interfacial spin–orbit coupling effect related to the Cr insertion. Thus, SOT-induced magnetization switching was achieved under a relatively small critical current density of the order of 106 A/cm2 owing to the improved SOTs in the Pt/Co/Cr/Ta system. Our results indicate that the PMA and SOTs in Pt/Co/Cr/Ta structures can be enhanced via a Cr interfacial decoration.

Current-Induced Domain Wall Motion and Tilting in Perpendicularly Magnetized Racetracks

The influence of C insertion on Dzyaloshinskii–Moriya interaction (DMI) as well as current-induced domain wall (DW) motion (CIDWM) and tilting in Pt/Co/Ta racetracks is investigated via a magneto-optical Kerr microscope. The similar DMI strength for Pt/Co/Ta and Pt/Co/C/Ta samples reveals that DMI mainly comes from the Pt/Co interface. Fast DW velocity around tens of m/s with current density around several MA/cm2 is observed in Pt/Co/Ta. However, it needs double times larger current density to reach the same magnitude in Pt/Co/C/Ta, indicating DW velocity is related to the spin-orbit torque efficiency and pinning potential barrier. Moreover, in CIDWM, DW velocity is around 103 times larger than that in field-induced DW motion (FIDWM) with current-generated effective field keeping the same magnitude as applied magnetic field, revealing that the current-generated Joule heating has an influence on DW motion. Interestingly, current-induced DW tilting phenomenon is observed, while this phenomenon is absent in FIDWM, demonstrating that the current-generated Oersted field may also play an essential role in DW tilting. These findings could provide some designing prospects to drive DW motion in SOT-based racetrack memories.

Hybrid nanogenerator of BaTiO3 nanowires and CNTs for harvesting energy

AbstractnLead-free piezoelectric nano-based generator with energy harvesting has drawn a great attention in the recent years. BaTiO3 as a lead-free material with high piezoelectric coefficient and dielectric constant has been widely examined to realize nanogenerators. In this work, high-quality BaTiO3 (BTO) nanowires were prepared by hydrothermal synthesis as the piezoelectric material and then BTO/PVDF-based nanogenerators have been fabricated. Furthermore, the CNTs were added to improve the output voltage performance of the nanogenerator. It shows high performance of a maximum output voltage density of 7.3xa0V/cm2 and the stable current density of 3.3xa0nA/cm2. This hybrid nanogenerator with enhanced performance is a potential material for the application in harvesting energy, self-powered electronics and low-frequency capacitors.