Off-plane polarization in two dimensional materials is significant during the designation of functional nano-devices. As a prototype, the metal chalcogen-diphosphate CuInP 2 S 6 monolayer is selected, and the structure transition from the initial antiferroelectric (AFE) state to off-plane ferroelectric (FE) state is realized under the combined action of normal strain and electric field. With the introduce of compressed strain, the critical driven field for the transition is remarkably lowered, which is favorable for actual device operation and avoids the possible breakdown of film. As the compressed strain increases, the FE state changes to ground state, and the height of barrier between AFE state and FE state is lowered simultaneously. It is confirmed that the FE state keeps stable at room temperature even if the strain and the electric field are removed. Furthermore, the band gap of the monolayer changes from indirect to direct as the structure transition occurs, which will have potential photovoltaic applications. We hope our theoretical investigation can supply an alternative avenue to modify and improve the functionality of low-dimensional materials.

Cr 2 O 3 nanoparticles were prepared via one-step reactive laser ablation of Cr in oxygen. The metastable CrO 2 phase was obtained through the subsequent oxidation of Cr 2 O 3 nanoparticles under O 2 with gas pressures of up to 40 MPa. The as-prepared Cr 2 O 3 nanoparticles are spherical or rectangular in shape with sizes ranging from 20 nm to 50 nm. High oxygen pressure annealing is effective in producing meta-stable CrO 2 from as-dried Cr 2 O 3 nanoparticles, and the Cr 2 O 3 nanoparticles exhibit a weak ferromagnetic behavior with an exchange bias of up to 11 mT that can be ascribed to the interfacial exchange coupling between uncompensated surface spins and the antiferromagnetic core. The Cr 2 O 3 /CrO 2 nanoparticles exhibit an enhanced saturation magnetization and a reduced exchange bias with an increasing faction of CrO 2 due to the elimination of uncompensated surface spins over the Cr 2 O 3 nanoparticles when exposed to a high pressure of O 2 and/or possible phase segregation that results in a smaller grain size for both Cr 2 O 3 and CrO 2 .

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A ferromagnetic monolayer with competing long-range dipolar interaction, short-range interaction and magnetic uniaxial anisotropy is studied using Monte Carlo simulation. Striped domain patterns are found and reveal the microstructure of the magnetization transition at the ground state via the competing between dipolar interaction and uniaxial anisotropy. We present the finite temperature phase diagram and find a temperature-induced magnetization reorientation from out-of-plane to in-plane phase. The influence of the various interactions on the structure of the striped phase and reorientation behavior has been discussed.

The influnence of the amplitude (H0) and frequency of sweeped magnetic field on the exchange bias He and coercivity Hc for ferromagnetic/ antiferromagnetic films has been simulated with Monte Carlo method. In a cycle, the sweeped frequency is inversely proportional to Monte Carlo steps (MCSs). It is observed that, for smaller MCSs, the values of He and the blocking tempreture Tb reduce evidently with increasing MCSs; for larger MCSs, the values of He and Tb decrease gently with increasing MCSs. It is also found the values of He and Tb decrease obviously with increasing values of H0 (HN0). However, on the contrary, the value of Hc increases with increasing values of H0 (HN0). At low temperature and little HN0, the asymmetric loop may appear, which is attributed to the competition between the relaxation time and the period of the external magnetic field. Moreover, the symmetry of the loops influences evidently the values of He and Hc.