Novel Fe_3O_4@SiO_2@Ag@Ni trepang-like nanocomposites:High-efficiency and magnetic recyclable catalysts for organic dye degradation

A facile step-by-step approach is developed for synthesizing the high-efficiency and magnetic recyclable Fe_3O_4@SiO_2@Ag@Ni trepang-like nanocomposites.This method involves coating Fe_2O_3 nanorods with a uniform silica layer,reduction in 10%H_2/Ar atmosphere to transform the Fe_2O_3 into magnetic Fe_3O_4,and finally depositing Ag@Ni core-shell nanoparticles on the L-lysine modified surface of Fe_3O_4@SiO_2 nanorods.The fabricated nanocomposites are further characterized by x-ray diffraction,transmission electron microscopy,scanning electron microscope,Fourier transform infrared spectroscopy,and inductively coupled plasma mass spectroscopy.The Fe_3O_4@SiO_2@Ag@Ni trepang-like nanocomposites exhibit remarkably higher catalytic efficiency than monometallic Fe_3O_4@SiO_2@Ag nanocomposites toward the degradation of Rhodamine B(RhB) at room temperature,and maintain superior catalytic activity even after six cycles.In addition,these samples could be easily separated from the catalytic system by an external magnet and reused,which shows great potential applications in treating waste water.     

Structural and physical properties of BiFeO3 thin films epitaxially grown on SrTiO3（001） and polar（111） surfaces

The influence of surface polarity on the structural properties of BiFeO3 （BFO） thin films is investigated. BFO thin films are epitaxially grown on SrTiO3 （STO） （100） and polar （111） surfaces by oxygen plasma-assisted molecular beam epitaxy. It is shown that the crystal structure, surface morphology, and defect states of BFO films grown on STO substrates with nonpolar （001） or polar （111） surfaces perform very differently. BFO/STO （001）is a fully strained tetragonal phase with orientation relationship （001）[100]BFOII（001）[100]STO, while BFO/STO （111） is a rhombohedral phase. BFO/STO （111） has rougher surface morphology and less defect states, which results in reduced leakage current and lower dielectric loss. Moreover, BFO films on both STO （001） and STO （111） are direct band oxides with similar band gaps of 2.65 eV and 2.67 eV, respectively.     

Oscillation of coercivity between positive and negative in MnxGe1-x：H ferromagnetic semiconductor films

Amorphous MnxGe1-x :H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron cosputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1-x :H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1-x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6 :H film, the inverted Hall loop is also observed at 30 K, which is consistent with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1-x films for the application in spintronics.     

Multi-polar resistance switching and memory effect in copper phthalocyanine junctions

Copper phthalocyanine junctions, fabricated by magnetron sputtering and evaporating methods, show multi-polar （unipolar and bipolar） resistance switching and the memory effect. The multi-polar resistance switching has not been observed simultaneously in one organic material before. With both electrodes being cobalt, the unipolar resistance switching is universal. The high resistance state is switched to the low resistance state when the bias reaches the set voltage. Generally, the set voltage increases with the thickness of copper phthalocyanine and decreases with increasing dwell time of bias. Moreover, the low resistance state could be switched to the high resistance state by absorbing the phonon energy. The stability of the low resistance state could be tuned by different electrodes. In Au/copper phthalocyanine/Co system, the low resistance state is far more stable, and the bipolar resistance switching is found. Temperature dependence of electrical transport measurements demonstrates that there are no obvious differences in the electrical transport mechanism before and after the resistance switching. They fit quite well with Mott variable range hopping theory. The effect of A1203 on the resistance switching is excluded by control experiments. The holes trapping and detrapping in copper phthalocyanine layer are responsible for the resistance switching, and the interfacial effect between electrodes and copper phthalocyanine layer affects the memory effect.     

Controlled synthesis of ferromagnetic MnSe_x particles

The MnSe_x(x = 1,2) nanoparticles were synthesized under hydrothermal condition,by reaction of the reduced selenium and Mn~(2+) ion in the presence of hydrazine and acetic acid.By precisely controlling the pH value of the solution,a series of MnSe_x particles were synthesized.The structure and morphology of as-prepared particles were examined with x-ray diffractometer(XRD),transmission electron microscopy(TEM),and scanning electron microscopy(SEM).The average sizes of as-prepared particles varied from nanoscale to microscale with pH value increase.Furthermore,the nucleation and growth mechanism associated with pH values were discussed,which can be applied to the hydrothermal synthesis of metal chalcogenide in general.Finally,the optical and magnetic properties of as-prepared particles were measured.All as-made particles exhibit a ferromagnetic behavior with low coercivity and remanence at room temperature.     

Spin-independent transparency of pure spin current at normal/ferromagnetic metal interface

The spin transparency at the normal/ferromagnetic metal(NM/FM) interface was studied in Pt/YIG/Cu/FM multilayers. The spin current generated by the spin Hall effect(SHE) in Pt flows into Cu/FM due to magnetic insulator YIG blocking charge current and transmitting spin current via the magnon current. Therefore, the nonlocal voltage induced by an inverse spin Hall effect(ISHE) in FM can be detected. With the magnetization of FM parallel or antiparallel to the spin polarization of pure spin currents(σ(sc)), the spin-independent nonlocal voltage is induced. This indicates that the spin transparency at the Cu/FM interface is spin-independent, which demonstrates that the influence of spin-dependent electrochemical potential due to spin accumulation on the interfacial spin transparency is negligible. Furthermore, a larger spin Hall angle of Fe_(20)Ni_(80) (Py) than that of Ni is obtained from the nonlocal voltage measurements.     

Synchronization of nanowire-based spin Hall nano-oscillators

The synchronization of the spin Hall nano-oscillator (SHNO) device driven by the pure spin current has been investigated with micromagnetic simulations. It was found that the power spectra of nanowire-based SHNO devices can be synchronized by varying the current flowing in the heavy metal (HM) layer. The synchronized signals have relatively high power and narrow linewidth, favoring the potential applications. We also found that the synchronized spectra are strongly dependent on both the number and length of nanowires. Moreover, a periodic modulation of power spectra can be obtained by introducing interfacial Dzyaloshinskii-Moriya interaction (iDMI). Our findings could enrich the current understanding of spin dynamics driven by the pure spin current. Further, it could help to design novel spintronic devices.     

The origin of spin current in YIG/nonmagnetic metal multilayers at ferromagnetic resonance

Spin pumping in yttrium-iron-garnet(YIG)/nonmagnetic-metal(NM) layer systems under ferromagnetic resonance(FMR) conditions is a popular method of generating spin current in the NM layer.A good understanding of the spin current source is essential in extracting spin Hall angle of the NM and in potential spintronics applications.It is widely believed that spin current is pumped from precessing YIG magnetization into NM layer.Here,by combining microwave absorption and DC-voltage measurements on thin YIG/Pt and YIG/NM_1/NM_2(NM_1 =Cu or Al,NM_2 =Pt or Ta),we unambiguously showed that spin current in NM,instead of from the precessing YIG magnetization,came from the magnetized NM surface(in contact with thin YIG),either due to the magnetic proximity effect(MPE) or from the inevitable diffused Fe ions from YIG to NM.This conclusion is reached through analyzing the FMR microwave absorption peaks with the DC-voltage peak from the inverse spin Hall effect(ISHE).The voltage signal is attributed to the magnetized NM surface,hardly observed in the conventional FMR experiments,and was greatly amplified when the electrical detection circuit was switched on.