Narrow Results

A new and efficient algorithm is presented for the calculation of the partition function in the S=±1 Ising model. As an example, we use the algorithm to obtain the thermal-dependence of the magnetic spin susceptibility of an Ising antiferromagnet for a 8×8 square lattice with open boundary conditions. The results agree qualitatively with the prediction of the Monte Carlo simulations and the experimental data, and they are better than the mean field approach results. For the 8×8 lattice, the algorithm reduces the computation time by nine orders of magnitude.

In this paper, we present ab initio calculations within density functional theory (DFT) to investigate structure, electronic and magnetic properties of Ru₂CrZ (Z = Si, Ge and Sn) full-Heusler alloys. We have used the developed full-potential linearized muffin tin orbitals (FP-LMTO) based on the local spin density approximation (LSDA) with the PLane Wave expansion (PLW). In particular, we found that these Ruthenium-based Heusler alloys have the antiferromagnetic (AFM) type II as ground state. Then, we studied and discussed the magnetic properties belonging to our different magnetic structures: AFM type II, AFM type I and ferromagnetic (FM) phase. We also found that Ru₂CrSi and Ru₂CrGe exhibit a semiconducting behavior whereas Ru₂CrSn has a semimetallic-like behavior as it is experimentally found. We made an estimation of Néel temperatures (T_N) in the framework of the mean-field theory and used the energy differences approach to deduce the relevant short-range nearest-neighbor (J₁) and next-nearest-neighbor (J₂) interactions. The calculated T_N are somewhat overestimated to the available experimental ones.

Structural and magnetic properties as well as the electronic structures of ${\mathrm{\text{Ru}}}_2\mathrm{\text{YGe}}(\mathrm{\text{Y}}=\mathrm{\text{Cr}},\mathrm{\text{Mn}})$ Heusler alloys were investigated in the framework of first principle calculation. Using the full-potential linearized augmented plane wave (FP-LAPW) in connection with the generalized gradient approximation (GGA) treatment of exchange-correlation energy, we have performed the structural optimization in the non-magnetic (NM) and three different magnetic configurations: FM, AFM-I and AFM-II. We have found that our two compounds are stable for the AFM-II state, which agree with the available experimental and theoretical results. The exchange constants $J_1$ and $J_2$ as well as the temperature of transition to the paramagnetic state $(T_N)$ were estimated here by the use of the energy difference method and the mean field approximation. The electronic structure of our compounds in their magnetic state was also studied. The GGA + U method has also been used to take into account the strong correlations among the d orbitals of $\mathrm{\text{Ru}},\mathrm{\text{Cr}}$ and $\mathrm{\text{Mn}}$ atoms. This has considerably improved both the electronic and magnetic results which became close to the corresponding experimental data. We have finally studied the thermodynamic properties using the quasi-harmonic Debye model as implemented in the Gibbs Program.

In this paper, we have calculated the structural, electronic, magnetic and optical properties of Sr₂NiO₃ and Sr₂CoO₃ using density functional theory (DFT) within generalized gradient approximation (GGA). The crystal structure of both materials is well described with Immm (No. 71) symmetry which are isostructural with Sr₂CuO₃ and both are quasi-one-dimensional (1D) rectangular lattice G-type antiferromagnets, in consistent with the experimental data.

Due to a distortion, Sr₂CoO₃ lifts the near-degeneracy $d_{xz}$ and $d_{yz}$ states of the local Co electronic configuration, which demonstrates a strong coupling between the structural lattice and the electronic configuration. The calculated band structure shows a band gap of 1.376 eV for Sr₂NiO₃ and a band gap of 1.735 eV for Sr₂CoO₃. Ni and Co ions are in the high-spin $S=1$ and $S=3/2$ configurations with the magnetic moments of 1.585 ${\mu }_B$ and 2.587 ${\mu }_B$, respectively. Based on the Heisenberg Hamiltonian model, we conclude that the superexchange intrachain TM–O–TM superexchange interaction is predominant and interaction between the 1D chains is weak. According to the calculated dielectric function, absorption spectrum and electron energy loss spectrum, the optical responses suggest that Sr₂NiO₃ shows the unique anisotropic structure and interaction of the application in optoelectronics.

The manipulation and detection of antiferromagnetic (AFM) in exchange bias (EB)-based MRAM using spin-orbit torque (SOT) holds promise for developing highly reliable and ultrafast spintronic memory devices. However, the high switching current induced by the SOT-induced EB field remains a major drawback. Additionally, the mechanism behind the interaction between the EB field and the SOT remains unclear. To address this issue, we have introduced a thin layer of Mo between the AFM and ferromagnetic-free layers to tune the EB field and study the SOT-induced switching properties. Our findings indicate that when the SOT is dominant during short pulses of a few nanoseconds, Mo insertion can significantly reduce the EB field and decrease the SOT switching current, leading to a reduction in power consumption of these memories. This approach could open up new possibilities for optimizing EB-MRAM and improving our understanding of AFM electronics.

The electrical excitation of spin dynamics in antiferromagnets is important for the development of high-speed spintronic devices with a low power consumption. Here, we present a theoretical study of the spin dynamics generated in the Ni/Cu/Mn₂Au/Cu/Ni nanostructure by a perpendicular-to-plane electric current. Our investigation includes atomistic simulations of spin reorientations in a few monolayer antiferromagnetic Mn₂Au film and numerical calculations of nonequilibrium spin accumulation in the nanostructure comprising ferromagnetic Ni polarizers with antiparallel magnetizations. This combined approach enables us to quantify the dynamics of Mn magnetic moments induced by the spin-transfer torque created by the spin-polarized charge flow. The calculations show that the direct electric current with the density exceeding some temperature-dependent threshold value gives rise to steady-state auto-oscillations of the Néel vector in the $(001)$-oriented Mn₂Au nanolayer. As the precession of Mn magnetic moments occurs around an out-of-plane direction strongly deflected from their initial in-plane orientations, the emergence of auto-oscillations should be regarded as the realization of a dynamic spin reorientation transition in the antiferromagnetic crystal. Remarkably, the precession frequency rises with increasing current density J and exceeds 1THz at $J\approx 1.4\times 10^{13}$Am${}^{-2}$, which makes the described antiferromagnetic spin transfer nano-oscillator attractive for device applications. Furthermore, our simulations demonstrate that a picosecond current pulse injected into the Ni/Cu/Mn₂Au/Cu/Ni nanostructure can induce a precessional switching of the Néel vector. Depending on the current density and pulse duration, the Néel vector rotates by either 90° or 180° and attains stable orientation along the corresponding $〈110〉$ easy axis in the plane of the Mn₂Au nanolayer. This feature shows that the Ni/Cu/Mn₂Au/Cu/Ni nanostructure could be used as a nonvolatile memory cell with the electrical writing and readout.

Current-induced spin–orbit torque (SOT) switching is an efficient manipulation of noncollinear antiferromagnet states with exotic topological transport properties. However, stable switching of the spin chirality is still challenging, and the role of symmetry in SOT-driven switching is unclear. Here, we introduce asymmetric interfacial Dzyaloshinskii–Moriya interaction (DMI) by varying the value of one of the DMI vectors ($D_3)$. By using an atomistic model, it is shown that in Mn₃Ir monolayer, stable spin chiral switching driven by SOT can be realized. In particular, it can effectively reduce the critical switching current density and the switching time by increasing the value of $D_3$. We also provide switching phase diagrams with different $D_3$ and SOT coefficients. Our results help further understand the switching mechanism of antiferromagnets and develop promising applications of antiferromagnetic (AFM) spintronic devices.