Stochastic resonance (SR) is a phenomenon wherein an information-carrying signal is enhanced via noise in a nonlinear system. This phenomenon enables living beings to adapt to noisy environments and ...use environmental noise to obtain useful information. A novel activation function of the echo state network (ESN) based on bistable SR is proposed in this study. Instead of using the tanh activation function—which is representative of the traditional threshold activation function—the bistable SR activation function is used to improve the noise adaptability of the ESN. Further, the proposed activation function provides a short-term memory (STM) ability that is not provided by the widely used threshold activation function, and thus, a physical reservoir can be designed using the proposed function. An STM task and a parity check task are used to verify the short-term memory and nonlinear ability of the bistable SR activation function. Further, two different prediction benchmarks prove that the proposed activation function can improve the noise adaptability of ESN. Finally, a visual recognition task is performed to demonstrate the potential of the SR activation function for physical reservoir computing.
The physical implementation of reservoir computing (RC), a brain-inspired computing framework, is attracting increasing attention in various research fields owing to its capability of quick learning ...and the relatively simple training process. Although several physical RC models have been envisaged and realized, most of them require additional peripherals; it leads to an increase in the power consumption of the system. In this study, we propose a novel RC model that is based on an overdamped bistable system and exhibits a counter-intuitive phenomenon called stochastic resonance, through which it can transfer noise energy to the information-carrying signal to realize learning with a comparatively low power consumption. The proposed model also possesses the functional capability of filtering and amplification and thus does not require additional peripheral equipment. In order to prove the feasibility and determine the desired operation mode of the system, two basic benchmark tests, namely short-term memory and parity check tasks, were employed to assess the proposed model. The results verify that this work will potentially act as a stepping stone towards realizing even better low-power-consumption physical RC.
Alteration of the hydrogen-bond (H-bond) network by trehalose is acknowledged as a bioprotective agent. However, most studies exploring the hydration superiority of the trehalose structure are ...limited structure are limited by the computational cost or a narrow-range spectrum. In the present study, the structural and dynamical behaviors of the H-bond network of trehalose and maltose solutions were observed and compared with a broadband dielectric spectrum (100 MHz–18 THz) to investigate the influence of the trehalose structure on the bioprotective function. From the relaxation time, the reorientation cooperativity, resonant frequency, and damping constant of water–water vibration, the symmetric structure of trehalose allowed a more significant H-bond strengthening effect and homogeneous aqueous environment. In contrast, the difference in the hydration number between trehalose and maltose was negligible. Thus, the enhanced H-bond strengthening effect and homogeneous aqueous environment owing to the symmetric structure are the essential factors that contribute to the remarkable bioprotective effect of trehalose.
•Co2+ and Si4+-substituted Lu3Fe5O12 thin films were prepared by a PLD.•Magnetic measurements reveal the presence of spin cluster glass behaviors below TG = 190–220 K.•FMR study has confirmed ...increased perpendicular anisotropy energy induced by Co substitution.•Spin wave characteristics have been investigated in wide temperature range from 50 K to 450 K.
In this study, lutetium iron garnet (Lu3Fe5O12; LuIG) thin films have been grown on Y3Al5O12 (1 1 1) substrates by a pulsed laser deposition and are co-substituted with strong magnetically anisotropic ions of Co2+ and nonmagnetic ones of Si4+. LuIG is a garnet-structured ferrimagnet with an exceptionally low Gilbert damping constant as 10−5. The substitution of Co2+ and Si4+ induces a chemical disorder and competing antiferromagnetic and ferromagnetic interactions, which induce a spin glass behavior. When the Co–Si substitution ratio is increased, a spin-freezing behavior is observed below the spin-freezing temperature TG = 190–220 K of the Lu3Fe4Co0.5Si0.5O12 film; this indicates the presence of a cluster glass phase. The film demonstrates a characteristic memory effects in the temperature range 120–180 K, which are below TG; this reveals the presence of a metastable magnetic state in the multi-valley energy landscape with shallow activation energy barriers. Ferromagnetic resonance measurements confirm increased perpendicular anisotropy energy induced by Co substitution and spin-wave characteristics including the inverse spin Hall effect voltage (VISHE). Lu3Fe5-2xCoxSixO12 films show an increase in damping and a decrease in VISHE at the cryogenic temperature, which are attributed to the impurity relaxation mechanism. Therefore, the Co- and Si-substituted films exhibit strong spin-wave damping at a low temperature, which reflects the spin-freezing dynamics of cluster glass behaviors.
•The phase locking behavior of superparamagnetic tunnel junctions (STJs) as stochastic magnetic bits induced by colored noise is studied.•White, blue and violet noise can promote the subthreshold STJ ...synchronization.•The phase locking of STJs is suppressed by pink noise and red noise.•Blue noise can make STJs get the lowest phase locking power consumption with order of 10−13J.
Superparamagnetic tunnel junctions (STJs) are nanostructures with very low turnover barriers. The barrier height of an STJ is generally equal to the heat energy at room temperature; thus, it can oscillate automatically without external driving. Previous studies have shown that the randomness of an STJ can be driven by a subthreshold voltage. This synchronization can be adjusted using electrical noise, which is often considered as zero-field Gaussian white noise. However, the actual circuit and environment are inevitably associated with colored noise, which has not been considered previously. In this work, numerical simulations were performed to study the phase-locking characteristics of a single STJ with the aid of several typical types of colored noise. The results show that the phase-locked behavior of an STJ can be effectively enhanced by colored noise whose power spectral density per unit of bandwidth is proportional to its frequency. Meanwhile, colored noise whose power spectral density per unit of bandwidth and frequency are inversely proportional can suppress the synchronization of STJs by suppressing the increase in junction frequency.
Abstract
Reservoir computing is a brain heuristic computing paradigm that can complete training at a high speed. The learning performance of a reservoir computing system relies on its nonlinearity ...and short-term memory ability. As physical implementation, spintronic reservoir computing has attracted considerable attention because of its low power consumption and small size. However, few studies have focused on developing the short-term memory ability of the material itself in spintronics reservoir computing. Among various magnetic materials, spin glass is known to exhibit slow magnetic relaxation that has the potential to offer the short-term memory capability. In this research, we have quantitatively investigated the short-term memory capability of spin cluster glass based on the prevalent benchmark. The results reveal that the magnetization relaxation of Co, Si-substituted Lu
3
Fe
5
O
12
with spin glass behavior can provide higher short-term memory capacity than ferrimagnetic material without substitution. Therefore, materials with spin glass behavior can be considered as potential candidates for constructing next-generation spintronic reservoir computing with better performance.
Near-zero-index materials and structures, with their extraordinary optical behaviors of phase-free propagation resulting in directional radiation, provide a possible approach for directional coupling ...and optical logic gates in photonic integrated circuits. However, the radiation from the near-zero-index structures is limited to a short range of a few hundreds of nanometers. A Bloch surface wave (BSW), an electromagnetic surface wave that can be excited at the interface between an all-dielectric multilayer and a dielectric medium with a low-loss optical mode, provides a solution to increase the propagation length. In this work, we present a nanostructured near-zero-index slab integrated on the all-dielectric metal-free BSW platform for long-range surface wave radiation. By employing the long-range directional surface-wave radiation, a directional coupler and optical logic gates based on the BSW near-zero-index slabs are realized. The proposed directional couplers achieve long coupling distances (the electric-field magnitude ratio between the input slab and output slab is 0.22 with a 50 μm coupling distance), which is 2 orders of magnitude longer than that of conventional directional couplers based on evanescent wave coupling. By controlling the interference pattern of the BSW between the slabs, the XOR logic gate is experimentally demonstrated with a significant extinction ratio of 27.9 dB at telecommunications wavelengths. The BSW near-zero-index logic gates and the directional coupler with long-range light propagation provide an approach to the development of photonic integrated circuits and metal-free surface wave-based applications.
Spin waves (SWs) have tremendous application potential in wave-based computation utilizing a broad frequency spectrum spanning from the gigahertz-to-terahertz ranges. Like optical and other ...electromagnetic waves, SWs also promise to usher in a new era of parallel data processing with low-power consumption without Joule heating. However, this potential is undermined by the lack of investigation on multichannel networking and operation on single chips under a uniform bias magnetic field. This study proposes a multifrequency SW propagation based on shape anisotropy in microstructured rectangular waveguides made of yttrium iron garnet (YIG). The width-dependent transmission properties of magnetostatic surface SWs in the YIG waveguides were experimentally demonstrated. We revealed that the smaller width of the waveguide results in lower SWs frequency due to the demagnetizing field along the width direction. Multifrequency SW propagation was demonstrated in a device where three waveguides with widths of 10, 20, and <inline-formula> <tex-math notation="LaTeX">100~\mu \text{m} </tex-math></inline-formula> were connected to the common antennas. SWs propagation with the frequencies of 1.98, 2.11, and 2.18 GHz have been transmitted under a uniform bias magnetic field. Furthermore, we investigated SWs transmission in a device where three waveguides with different widths were interconnected at their ends and under one side of the antenna. We observed that the interconnected waveguides result in a single resonant frequency with flat band transmission because the whole waveguide structure is considered a single magnetic body. The results presented here provide guidelines for complex networks in frequency-division multiplexing operation.
We present a comparison of the spin wave propagation in Au/Y3Fe5O12 and Pt/Y3Fe5O12 bilayers. Microwave technique with a co-planner waveguide arrangement was used to excite and detect the spin wave. ...We observed a suppression in the propagating spin wave intensity when a metal stripe is placed on the surface of Y3Fe5O12 in the spin wave propagation path due to the spin pumping from Y3Fe5O12 to nonmagnetic metal stripe. However, a significant difference in the suppression property was observed with the Au and Pt electrode layers, which cannot be explained by the enhancement of the damping constant induced by spin pumping alone. The significant suppression of the spin wave propagation in the Au/Y3Fe5O12 bilayer system is attributed to the spin backflow and two magnon scattering.
•A nano-zigzag pattern is self-organized in the manganite thin films grown by pulsed laser deposition.•A thermal annealing treatment promotes crystalline phase separation in nanoscale driven by the ...Jahn-Teller effect.•The magnetic properties strongly depend on the annealing time, which can be attributed to the inter-diffusion of cations.
The fabrication of highly-ordered nanostructures by self-organization is one of the greatest challenges in nano science. Herein, we report the formation of a self-organized nanostructure in the CoGa0.8Mn1.2O4 thin film through a thermal annealing treatment. The thin film as-deposited by pulsed laser deposition exhibits a single crystalline phase epitaxially oriented along the 001 direction the SrTiO3 001 substrate. Post-annealing in air was found to promote crystalline phase separation into tetragonal and cubic phases driven by the Jahn–Teller effect resulting in the formation of the nano-zigzag pattern. The structural and magnetic properties of the nanostructured films strongly depend on the annealing time, which can be attributed to the inter-diffusion of Ga and Mn ions.
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