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The analog switching behavior of resistive random access memory (RRAM) is crucial for its application in neuromorphic computing. This paper investigates the switching mechanism of RRAM under sub-nanosecond and nanosecond pulse programming, with selected device materials and structures, using the kinetic Monte Carlo simulation method. The microscopic distribution of oxygen vacancies is simulated in all three spatial dimensions and in the time dimension (four-dimensional). According to the simulation results, thermal effects are a critical factor affecting the switching behavior. The thermal effects inside the HfOx switching layer can be almost completely eliminated by using sub-nanosecond pulses with low voltage, finally leading to good analog behavior. When nanosecond pulses are applied, effective heat insulation is the key to realizing analog characteristics. In general, the switching process is proposed to involve three stages. Having the lowest energy consumption, the first stage shows the greatest potential for achieving analog behavior. The use of heat-isolating structures, like capping layers and side wall materials with lower thermal conductance, could be a solution to improve the analog behavior of RRAM at the first stage when down-scaling the device size. [ABSTRACT FROM AUTHOR]

Enhanced transmission, and specifically tunable enhanced transmission, of microwaves through a subwavelength metal aperture is of major significance for a variety of microwave applications. In this study, by placing a metamaterial resonator into a subwavelength aperture, we experimentally and numerically demonstrated a transmission enhancement of 20 dB at the first Mie resonant frequency of this metamaterial resonator. Importantly, this enhanced transmission is also thermally tunable because of the high temperature coefficient of resonant frequency of the dielectric-based metamaterial resonator. Over a temperature range from 20 °C to 90 °C, the enhanced transmission peak was adjusted from 11.6 GHz to 12.1 GHz. Therefore, thermally tunable enhanced transmission of microwaves through a subwavelength metal aperture was realized. [ABSTRACT FROM AUTHOR]

The magnetic anisotropy is of both scientific and technological interest for magneto-optical material GdFeCo film. We characterize the magnetic anisotropy of a 20 nm GdFeCo film from 265 K to 320 K via Kerr loops and ferromagnetic resonance. With increasing temperature, both of the first-order uniaxial magnetic anisotropy and shape anisotropy increase. However, the competition between them causes a temperature-driven spin reorientation transition (SRT) and the effective perpendicular magnetic anisotropy decrease from 2.22 x 104ergs/cm³ (288K) to --1.56 x 104ergs/cm³ (317K). The positive second-order uniaxial magnetic anisotropy determines an easy-cone state as the mediated state during SRT. [ABSTRACT FROM AUTHOR]

We report an investigation on magnetic anisotropy of Co/Si(111) films deposited at oblique incidence. An in-plane uniaxial magnetic anisotropy (UMA) with the easy axis perpendicular to the incident flux plane was observed to superimpose on sixfold magnetocrystalline anisotropy of Co films. We built a total energy model to investigate the magnetization reversal mechanism around hard axis. The simulated value of UMA is Ku=1.7×105 erg/cm3, which is consistent with Kshape=1.1×105 erg/cm3 calculated from scanning tunneling microscope image. This good agreement suggests the in-plane UMA is mainly originated from the shape of the oblique deposited Co stripes. [ABSTRACT FROM AUTHOR]

Fe single crystal film with thickness of 45 monolayer was fabricated on vicinal Si(111) substrate using ultrathin p(2×2) iron silicide as buffer layer. Scanning tunneling microscope images show that the Fe nanoclusters form chains on vicinal substrate. The first- and second-order magnetocrystalline anisotropies, uniaxial magnetic anisotropy constants of the films were obtained by fitting the ferromagnetic resonance data. The sixfold symmetry of the in-plane resonance field for Fe(111) film was changed into the superposition of a fourfold and a twofold contribution due to the effect of the vicinal substrate. [ABSTRACT FROM AUTHOR]

Magnetic properties of irregular Fe islands grown on Si(111) substrate with Pb buffer layer by molecular beam epitaxy have been investigated by means of Monte Carlo simulation. During the simulation, the dipolar interaction energy among islands and the demagnetization energy of each island were accurately calculated in the Fourier space with the aid of cluster multiple labeling technique. The simulated results, i.e., the magnetic hysteresis loops and the temperature dependence of remanent magnetization, are in good agreement with the experimental ones measured by in situ surface magneto-optical Kerr effect (SMOKE). [ABSTRACT FROM AUTHOR]