Multiferroic materials are potential to be applied in novel magnetoelectric devices, for example, highdensity non-volatile storage. Last decades, research on multiferroic materials was focused on threedimensional (3D) materials. However, 3D materials suffer from the dangling bonds and quantum tunneling in the nano-scale thin films. Two-dimensional (2D) materials might provide an elegant solution to these problems, and thus are highly on demand. Using first-principles calculations, we predict ferromagnetism and driven ferroelectricity in the monolayer and even a few-layers of CuCrP2S6.Although the total energy of the ferroelectric phase of monolayer is higher than that of the antiferroelectric phase, the ferroelectric phases can be realized by applying a large electric field. Besides the degrees of freedoms in the common multiferroic materials, the valley degree of freedom is also polarized according to our calculations. The spins, electric dipoles and valleys are coupled with each other as shown in the computational results. In experiment, we observe the out-of-plane ferroelectricity in a few-layer CuCrP2S6 (approximately 13 nm thick) at room temperature. 2D ferromagnetism of fewlayers is inferred from magnetic hysteresis loops of the massively stacked nanosheets at 10 K. The experimental observations support our calculation very well. Our findings may provide a series of 2D materials for further device applications.

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Magnetic properties with three different sizes of Ni nanochains, synthesized by a technique of wet chemical solution, have been investigated experimentally. The sample sizes (average diameter of the nano-particles) are 50, 75, and 150 nm, with a typical length of a few microns. The characterizations by XRD and TEM reveal that the samples consist of Ni nano-particles forming a one-dimensional (1D) chain-like structure. Magnetic properties have been investigated by temperature dependent magnetization M(T ) and field dependent magnetization M(H ) measurements. The results are explained within the context of the core-shell model. First, the freezing of disordered spins in the shell layer has resulted in a peak structure on the zero-field-cooled (ZFC) M(T ) curve. The peak position is identified as the freezing temperature T F . It is well described by the de Almeida-Thouless (AT) equation for the surface spin glass state. Second, the shape anisotropy of the 1D structure has caused a wide separation between the field-cooled (FC) and ZFC M(T ) curves. This is mainly attributed to the blocking of the core magnetism by an anisotropy barrier, E A . Third, by the M(H ) measurement in the low field region, the open hysteresis loop measured at T = 5 K < T F is significantly enlarged in comparison with that taken at T > T F . This indicates that a significant part of the contribution to the magnetic irreversibility at T < T F is arising from the disordered spins in the shell layer. Last, with the reduced sample size, the coercivity, H C , increases whereas the saturation magnetization goes down substantially. These imply that, as the sample size reduces, the effect of shape anisotropy becomes larger in the magnetization reversal process and the contribution to the magnetism from the ferromagnetically ordered core becomes smaller.

Measurement of the orientation of acetabular components on plain AP radiographs is reliable and accurate compared with measurement on CT.