Semi-active vehicle suspension with magnetorheological dampers is a promising technology for improving the ride comfort of a ground vehicle. However, the magnetorheological damper always exhibits nonlinear hysteresis between its output force and relative velocity, and additional nonlinear stiffness owing to the state transition from liquid to semi-solid or solid, so that the semi-active suspension with magnetorheological dampers features nonlinearity by nature. To control such nonlinear dynamic systems subject to random road roughness, in this paper we present a neural network control, which includes an error back propagation algorithm with quadratic momentum of the multilayer forward neural networks. Both the low frequency of road-induced vibration of the vehicle body and the fast response of the magnetorheological damper enable the neural network control to work effectively on-line. The numerical simulations and an experiment for a quarter-car model indicate that the semi-active suspension with a magnetorheological damper and neural network control is superior to the passive suspensions in a range of low frequency.

Two-dimensional (2D) magnetic materials have attracted much attention due to their unique magnetic properties and promising applications in spintronics. Here, we report on the growth of ferrous chloride (FeCl2) films on Au(111) and graphite with atomic thickness by molecular-beam epitaxy (MBE) and the layer-dependent magnetic properties by density functional theory (DFT) calculations. The growth follows a layer-by-layer mode with adjustable thickness from sub-monolayer to a few layers. Four types of moiré superstructures of a single-layer FeCl2 on graphite and two types of atomic vacancies on Au(111) have been identified based on high-resolution scanning tunneling microscopy (STM). It turned out that the single- and few-layer FeCl2 films grown on Au(111) exhibit a 1T structure. The DFT calculations reveal that a single-layer 1T-FeCl2 has a ferromagnetic ground state. The minimum-energy configuration of a bilayer FeCl2 is satisfied for the 1T–1T structure with ferromagnetic layers coupled antiferromagnetically. These results make FeCl2 a promising candidate as ideal electrodes for spintronic devices providing large magnetoresistance.

Single-and few-layer chromium triiodide (CrI3), which has been intensively investigated as a promising platform for two-dimensional magnetism, was usually prepared by mechanical exfoliation. Here, we report on the growth of single-layer CrI3 by molecular beam epitaxy under ultrahigh vacuum. The atomic structures and local density of states have been revealed by scanning tunneling microscopy (STM). Iodine trimers, each of which consists of three I atoms surrounding a three-fold Cr honeycomb center, have been identified as the basic units of the topmost I layer. Different superstructures of single-layer CrI3 with characteristic periodicity around 2-4 nm were obtained on Au(111), but only pristine structure was observed on graphite.At elevated temperatures (423 K), CrI3 was partially decomposed, resulting in the formation of single-layer chromium diiodide. Our bias-dependent STM images suggest that the unoccupied and occupied states are distributed spatial-separately, which is consistent with our density functional theory calculations. The effect of charge distribution on the superexchange interaction in single-layer CrI3 was discussed.Keywords: two-dimensional magnetic materials, CrI3, molecular beam epitaxy, scanning tunneling microscopy 2 / 18 Two-dimensional (2D) magnetic materials, which serve as ideal platforms for investigating spin-related emergent phenomena at reduced dimensions and exhibit potential applications in optoelectronics and spintronics, 1,2 have long been sought. However, as revealed by Mermin-Wagner theorem, long-range magnetic order in 2D systems with isotropic local magnetic interactions are thermodynamically instable at finite temperatures owing to enhanced thermal fluctuations. 3 By introducing magnetic anisotropy, on the other hand, 2D magnetism may exist in a number of layered van der Waals (vdW) materials, for example, transition metal chacogenides and halides. 4-6 Among them, single-and bi-layer chromium triiodide (CrI3) has been recently confirmed with intralayer ferromagnetism (FM) and interlayer antiferromagnetism (AFM). 7,8 The FM coupling in single-layer CrI3, which exhibits a Curie temperature of 45 K, slightly lower than that of the bulk counterpart (61 K), is mainly ascribed to the superexchange interaction between the neighboring Cr atoms mediated by the bridging I atoms. 9 The easy magnetization direction is out of plane with an anisotropy energy about 0.50-0.69 meV/Cr, according to density functional theory (DFT) calculations. 10,11 The magnetic tunneling junction consisting of four-layer CrI3 sandwiched with two graphene layers as the electrodes performs a magnetoresistance change as large as 19,000%, 12 demonstrating the advantages of layered vdW materials for fabricating advanced spintronic devices. [12][13][14][15] Besides CrI3, other layered materials, such as Cr2Ge2Te6, CrCl3, CrBr3, Fe3GeTe2 and FePS3, have been already obtained and verified with long-range magnetic order. [16][17][18][19][20][21] So far, mechanical exfoliation is the major method for preparing 2D magn...