The electric-pulse-induced resistive switching effect is studied for Tio.s5Cro.15Ox （TCO） films grown on Ir-Si substrates by pulsed laser deposition. Such a TCO device exhibits bipolar switching behaviour with an electric-pulse- induced resistance ratio as large as about 1000% and threshold voltages smaller than 2 V. The resistive switching characteristics may be understood by resistance changes of a Schottky junction composed of a metal and an n-type semiconductor, and its nonvolatility is attributed to the movement of oxygen vacancies near the interface.
CoNiFe patterned films with rectangular elements, all 600-nm wide but of different lengths, were fabricated and inves- tigated by ferromagnetic resonance experiment and micromagnetic simulation. An in-plane magnetic uniaxial anisotropy was exhibited, and its value increases with the increase of the aspect ratio of the elements, which was fitted by the model, including a quasi-ellipsoid demagnetizing field and a non-uniform demagnetizing field. The relative importance of the non- uniform demagnetizing field decreased from 0.26 to 0.16 with the increase of the length-width aspect ratio of the patterned element from 1.5 to 10. The demagnetizing factors in the three principal axes were determined from the experimental data of ferromagnetic resonance, which agreed reasonably well with the values calculated by micromagnetic simulation. The calculation also indicated that the interaction between elements could be neglected when the edge-to-edge spacing between neighboring elements was larger than 3 μm in our patterned films.
The microwave slow-light delay-line has broad applications in signal processing systems,and the tunable slow-light delay-line is particularly important for adjusting the timing of wave packets and phased array beam shapers.We propose to construct multichannel microwave slow-light delay-lines using piezoelectric(PMN-PT)and piezomagnetic(CoFe_(2)O_(4))superlattices(PPS).The group velocity can be slowed down by a factor of 14612(31554)and a delay bandwidth product(DBP)of 25(47)can be achieved for the first(second)channels with a sample length of 1 cm around 10GHz(21 GHz).Furthermore,a tunable time-delay from 590 ps(590ps)to 480ns(1052 ns)can be realized by flipping the magnetic domains using an external magnetic field.The nonreciprocal polaritonic bands also contain the basic building blocks for designing the compact microwave isolator.
Giant resonance enhancement is demonstrated to be due to the Fano interference in a grating waveguide composed of gain-assisted silicon slabs. The Fano mode is characterized by its ultra-narrow asymmetric spectrum, different from that of a pure electric or magnetic dipole. The simulation indicates that a sharp Fano-interfered lineshape is responsible for the giant resonance enhancement featuring the small-gain requirements.
N-doped ZnO films were prepared in nitrogen plasma by pulsed laser deposition. Clear room temperature ferro- magnetism has been observed in the film prepared at a substrate temperature of 500 ℃. The structural characterizations of X-ray diffraction, Raman, and X-ray photoelectron spectroscopy confirm the substitution of O by N in ZnO, which has been considered to be the origin of the observed ferromagnetism. Furthermore, ferroelectricity has been observed at room temperature by piezoelectric force microscopy, indicating the potential multiferroic applications.
Bipolar resistive switching is studied in BiFe0.95Zn0.05O3 films prepared by pulsed laser deposition on （001） SrTiO3 substrate, with LaNiO3 as the bottom electrode, and Pt as the top electrode. Multiple steps of resistance change are ob- served in the resistive switching process with a slow voltage sweep, indicating the formation/rupture of multiple conductive filaments. A resistive ratio of the high resistance state （HRS） to the low resistance state （LRS） of over three orders of mag- nitude is observed. Furthermore, the conduction mechanism is confirmed to be space-charge-limited conduction with the Schottky emission at the interface with the top Pt electrodes in the HRS, and Ohmic in the LRS. Impedance spectroscopy demonstrates a conductive ferroelectric/interfacial dielectric 2-layer structure, and the formation/rupture of the conductive filaments mainly occurs at the interfacial dielectric layer close to the top Pt electrodes.
Anisotropic localization of Dirac fermions in graphene along both the x and y axes was studied using the transfer-matrix method. The two-parameter scaled behavior around the Dirac points was observed along the x axis with off-diagonal disorder. In contrast, the electronic state along the y axis with armchair edges was delocalized, which can be described well by single parameter scaling theory. This implies that the breakdown of the single-parameter scaling is related to the zigzag edge along the x axis. Furthermore, dimerization induced by the substrate suppresses the two-parameter scaling behavior along the x axis and preserves the delocalized state along the y axis. Our results also demonstrate anisotropic localization in graphene with diagonal disorder that can be tuned by dimerization.
A general model of a hybrid inteffacial domain wall （HIDW） in ferromagnetic/antiferromagnetic exchange biased bilayers is proposed, where an inteffacial domain wall is allowed to extend into either the ferromagnetic or antiferromagnetic layer or across both. The proposition is based on our theoretical investigation on thickness and field dependences of ferromagnetic domain wall （FMDW） and antiferromagnetic domain wall （AFDW）, respectively. Good match of the simulation to the hysteresis loops of a series of NiFe/FeMn exchange-biased bilayers confirms the existence of the HIDW, where the AFDW part is found to preferentially occupy the entire antiferromagnetic layer while the FMDW shrinks with the increased magnetic field as expected. The observed asymmetry between the ascending and descending branches of the hysteresis loop is explained naturally as a consequence of different partition ratios between AFDW and FMDW.
