Recent experiments revealed that monolayer α-RuCl 3 can be obtain by chemical exfoliation method and exfoliation or restacking of nanosheets can manipulate the magnetic properties of the materials. In this present paper, the electronic and magnetic properties of α-RuCl 3 monolayer are investigated by combining first-principles calculations and Monte Carlo simulations. From first-principles calculations, we found that the spin configuration FM corresponds to the ground state for α-RuCl 3 , however, the other excited zigzag oriented spin configuration has energy of 5 meV/atom higher than the ground state. Energy band gap has been obtained as 3 meV using PBE functionals. When spin-orbit coupling effect is taken into account, corresponding energy gap is determined to be as 57 meV. We also investigate the effect of Hubbard U energy terms on the electronic band structure of α-RuCl 3 monolayer and revealed band gap increases approximately linear with increasing U value. Moreover, spin-spin coupling terms (J 1 , J 2 , J 3 ) have been obtained using first principles calculations. By benefiting from these terms, Monte Carlo simulations with single site update Metropolis algorithm have been implemented to elucidate magnetic properties of the considered system. Thermal variations of magnetization, susceptibility and also specific heat curves indicate that monolayer α-RuCl 3 exhibits a phase transition between ordered and disordered phases at the Curie temperature 14.21 K. We believe that this study can be utilized to improve two-dimensional magnet materials.

Theoretical and experimental studies present that metal halogens in MX3 forms can show very interesting electronic and magnetic properties in their bulk and monolayer phases. Many MX3 materials have layered structures in their bulk phases, while RuBr3 and RuI3 have one-dimensional chains in plane. In this paper, we show that these metal halogens can also form two-dimensional layered structures in the bulk phase similar to other metal halogens, and cleavage energy values confirm that the monolayers of RuX3 can be possible to be synthesised. We also find that monolayers of RuX3 prefer ferromagnetic spin orientation in the plane for Ru atoms. Their ferromagnetic ground state, however, changes to antiferromagnetic zigzag state after U is included. Calculations using PBE+U with SOC predict indirect band gap of 0.70 eV and 0.32 eV for the optimized structure of RuBr3 and RuI3, respectively. Calculation based on the Monte Carlo simulations reveal interesting magnetic properties of RuBr3, such as large Curie temperature against RuI3, both in bulk and monolayer cases. Moreover, as a result of varying exchange couplings between neighboring magnetic moments, magnetic properties of RuBr3 and RuI3 can undergo drastic changes from bulk to monolayer. We hope our findings can be useful to attempt to fabricate the bulk and monolayer of RuBr3 and RuI3.

The magnetic properties of a spin-1 Blume-Capel (BC) model on a square lattice (q = 4) with a ferromagnetic interaction have been examined here by the use of Monte Carlo (MC) simulation technique and an introduced effective-field approximation (IEFT), which includes the correlations between different spins that emerge when expanding the identities. The effects of the external magnetic field and crystal field on the magnetic properties of the spin system are discussed in detail. In order to obtain credible results, a detailed comparison of the results obtained by the two methods has been made with those of the other methods in the literature. A number of interesting phenomena originating from the temperature, crystal field and external field have been found.

Transition metal boro-carbide (TM2BC) structures crystalize in the layered orthorhombic structure in their bulk phases. In this study, however, we find that TM2BC (TM = Cr, Mn) prefer tetragonal (t)...

In this manuscript, we have carried out a combined study of density functional theory and Monte Carlo (MC) simulations for a thorough examination of a single-layer (SL) Ti 2 B structure. On the basis of first-principles, spin-polarized density functional calculations, we showed that a free standing SL-Ti 2 B structure is dynamically and thermally stable. The atomic structure, phonon spectrum, electronic and magnetic properties of the SL-Ti 2 B structure are analyzed. In order to determine ground state, the structure of Ti 2 B is optimized for four types of spin oriented configurations, namely ferromagnetic (FM), antiferromagnetic Néel, antiferromagnetic Zigzag and antiferromagnetic Stripy and non-magnetic states. We found that the spin configuration FM corresponds to the ground state for SL-Ti 2 B . We also found that the Raman-active modes are softening in the antiferromagnetic cases. On the basis of these results, MC simulations show that the magnetic susceptibility, thermal variations of magnetization, and specific heat curves of Ti 2 B exhibit a phase transition between paramagnetic and FM phases at the Curie temperature of 39.06 K. While SL-Ti 2 B possess a little out-of-plane magnetic anisotropy, it has not any in plane magnetic anisotropy energy.