Search

Nonlinear dynamics of the magnetic vortex state in a circular nanodisk was studied under a perpendicular alternating magnetic field that excites the radial modes of the magnetic resonance. Here, we show that as the oscillating frequency is swept down from a frequency higher than the eigenfrequency, the amplitude of the radial mode is almost doubled to the amplitude at the fixed resonance frequency. This amplitude has a hysteresis vs. frequency sweeping direction. Our result showed that this phenomenon was due to a Duffing-type nonlinear resonance. Consequently, the amplitude enhancement reduced the vortex core-switching magnetic field to well below 10 mT. A theoretical model corresponding to the Duffing oscillator was developed from the Landau-Lifshitz-Gilbert equation to explore the physical origin of the simulation result. This work provides a new pathway for the switching of the magnetic vortex core polarity in future magnetic storage devices. [ABSTRACT FROM AUTHOR]

The skyrmion magnetic bubble in a ferromagnetic disk exhibits hypocycloidal gyrations contrary to the vortex gyration, showing a simple circular trajectory. To describe the hypocycloidal bubble gyration, a mass term is needed in Thiele's equation. In this study, we analytically derived both mass and spring constant term, which are crucial parameters for describing the bubble gyration. Values obtained by these analytic expressions were consistent with those obtained by simulations. We could find the dependences of these two terms on several external parameters, including the bubble radius. Especially using the radius's dependence, we could obtain regular polygonlike trajectories such as a square and a triangle confirmed by the numerical simulations. Based on this effective method to control the bubble gyration, the regular polygonlike trajectories of this skyrmion magnetic bubble make it possible to study the bubble gyration without time-resolved experiments. [ABSTRACT FROM AUTHOR]

We have observed unipolar-type resistance switching in an ultrathin niobium oxide film. An analysis of the temperature dependence of the resistance switching transport revealed that low-resistance state showed a type of electrical conduction typically observed in metals. The modification in chemical binding states of the film in different resistance states was studied using x-ray photoelectron spectroscopy. The analysis of XPS showed that metallic suboxides NbOδ (δ < 2), decomposed from some of Nb2O5 and NbO2 components of the film, were created after electroforming process, suggesting that the metallic suboxides are constituting elements of metallic channels in the low resistance state. [ABSTRACT FROM AUTHOR]

High-performance ultra-thin oxide layers are required for various next-generation electronic and optical devices. In particular, ultra-thin resistive switching (RS) oxide layers are expected to become fundamental building blocks of three-dimensional high-density non-volatile memory devices. Until now, special deposition techniques have been introduced for realization of high-quality ultra-thin oxide layers. Here, we report that ultra-thin oxide layers with reliable RS behavior can be self-assembled by field-induced oxygen migration (FIOM) at the interface of an oxide-conductor/oxide-insulator or oxide-conductor/metal. The formation via FIOM of an ultra-thin oxide layer with a thickness of approximately 2-5 nm and 2.5% excess oxygen content is demonstrated using cross-sectional transmission electron microscopy and secondary ion mass spectroscopy depth profile. The observed RS behavior, such as the polarity dependent forming process, can be attributed to the formation of an ultra-thin oxide layer. In general, as oxygen ions are mobile in many oxide-conductors, FIOM can be used for the formation of ultra-thin oxide layers with desired properties at the interfaces or surfaces of oxide-conductors in high-performance oxide-based devices. [ABSTRACT FROM AUTHOR]

Strong charge-spin coupling is found in a layered transition-metal trichalcogenide NiPS3, a van der Waals antiferromagnet, from studies of the electronic structure using several experimental and theoretical tools: spectroscopic ellipsometry, x-ray absorption, photoemission spectroscopy, and density functional calculations. NiPS3 displays an anomalous shift in the optical spectral weight at the magnetic ordering temperature, reflecting strong coupling between the electronic and magnetic structures. X-ray absorption, photoemission, and optical spectra support a self-doped ground state in NiPS3. Our work demonstrates that layered transition-metal trichalcogenide magnets are useful candidates for the study of correlated-electron physics in two-dimensional magnetic materials. [ABSTRACT FROM AUTHOR]