Origin of the Ising Ferrimagnetism and Spin-Charge Coupling in LuFe2O4

Nontrivial ferrimagnetism of the Heisenberg model on the Union Jack strip lattice

We study the ground-state properties of the S=1/2 antiferromagnetic Heisenberg model on the Union Jack strip lattice by using the exact-diagonalization and density matrix renormalization group methods. We confirm a region of the intermediate-magnetization state between the Neel-like spin liquid state and the conventional ferrimagnetic state of Lieb-Mattis type. In the intermediate-state, we find that the spontaneous magnetization changes gradually with respect to the strength of the inner interaction. In addition, the local magnetization clearly shows an incommensurate modulation with long-dis…

Two-Dimensional Semiconducting Metal Organic Frameworks with Auxetic Effect, Room Temperature Ferrimagnetism, Chiral Ferroelectricity, Bipolar Spin Polarization and Topological Nodal Lines/Points

Two-dimensional (2D) semiconductors integrated with two or more functions are the cornerstone for constructing multifunctional nanodevices, but remain largely limited. Here, by tuning the spin state of organic linkers and the symmetry/topology of crystal lattice, we predict a class of unprecedented multifunctional semiconductors in 2D Cr(II) five-membered heterocyclic metal organic frameworks that simultaneously possess auxetic effect, room temperature ferrimagnetism, chiral ferroe-lectricity, electrically reversible spin polarization and topological nodal lines/points. Taking 2D Cr(TDZ)$_2$ (…

单层NbTe2中的交替手性电荷密度波与混合亚铁磁性

Alternating-Chiral Charge Density Waves and Hybrid Ferrimagnetism in Monolayered NbTe2

本研究发现单层NbTe2中晶格、电荷与自旋自由度协同产生交替手性电荷密度波与混合亚铁磁序，揭示其关联驱动的起源，拓展了关联电子体系手性序研究并为手性自旋电子学提供新平台。

Ferrimagnetism in stable non-metal covalent organic framework

We synthesized a pure organic non-metal crystalline covalent organic framework TAPA-BTD-COF by bottom-up Schiff base chemical reaction. And this imine-based COF is stable in aerobic condition and room-temperature. We discovered that this TAPA-BTD-COF exhibited strong magneticity in 300 K generating magnetic hysteresis loop in M-H characterization and giant chimol up to 0.028. And we further conducted zero-field cooling and field-cooling measurement of M-T curves. The as-synthesized materials showed a large chi/mol up to 0.028 in 300 K and increasing to 0.037 in 4.0 K with 200 Oe measurement fi…

Origin of Ising magnetism in Ca3Co2O6 unveiled by orbital imaging

The one-dimensional cobaltate Ca3Co2O6 is an intriguing material having an unconventional magnetic structure, displaying quantum tunneling phenomena in its magnetization. Using a newly developed experimental method, s-core-level non-resonant inelastic x-ray scattering (s-NIXS), we were able to image the atomic Co 3d orbital that is responsible for the Ising magnetism in this system. We show that we can directly observe that it is the complex d2 orbital occupied by the sixth electron at the high-spin Co-trig{3+} (d6) sites that generates this behavior. This is extremely rare in the research fie…

Ising magnetism and ferroelectricity in Ca$_3$CoMnO$_6$

The origin of both the Ising chain magnetism and ferroelectricity in Ca$_3$CoMnO$_6$ is studied by $ab$ $initio$ electronic structure calculations and x-ray absorption spectroscopy. We find that Ca$_3$CoMnO$_6$ has the alternate trigonal prismatic Co$^{2+}$ and octahedral Mn$^{4+}$ sites in the spin chain. Both the Co$^{2+}$ and Mn$^{4+}$ are in the high spin state. In addition, the Co$^{2+}$ has a huge orbital moment of 1.7 $μ_B$ which is responsible for the significant Ising magnetism. The centrosymmetric crystal structure known so far is calculated to be unstable with respect to exchange st…

Mean field theory and Monte Carlo simulation of Phase transitions and Magnetic Properties of a tridimensional Fe7S8 Compound

The structural, electronic and magnetic properties of Fe7S8 material have been studied within the framework of the ab-initio calculations, the mean field approximation (MFA) and Monte Carlo simulation (MCS). Our study shows that two forms of the iron atoms, Fe2+ with spin S=2, and Fe3+ with spin σ=5/2 are the most probable configurations. A mixed Ising model with ferromagnetic spin coupling between Fe2+ and Fe3+ ions and between Fe3+ and Fe3+ ions, and with antiferromagnetic spin coupling between Fe2+ ions of adjacent layers has been used to study the magnetic properties of this compound. We d…

Logarithmic growth law in the two-dimensional Ising spin glass state resulting from the electron doping in single-layered manganites

The ac-susceptibility of the electron doped single-layered manganite La$_{1.1}$Sr$_{0.9}$MnO$_4$ is analyzed in detail. A quasi two-dimensional (2$D$) antiferromagnetic (AFM) order with Ising anisotropy is stabilized below $T_N$ $\sim$ 80K. We show that below $T_N$, a rare 2$D$ spin-glass (SG) correlation develops with the same Ising anisotropy as the AFM state. Using simple scaling arguments of the droplet model, we derive a scaling form for the ac-susceptibility data of a 2$D$ SG, which our experimental data follows fairly well. Due to simplifications in this 2$D$ case, the proposed scaling …

Magnetic origin of chemical balance in alloyed Fe-Cr stainless steels: first-principles and Ising model study

Iron-chromium forms the basis of most of the stainless steel grades in the markets. Recently new insights into the physical and chemical properties of Fe-Cr based alloys have been obtained. Some of the new results are quite unexpected and call for further investigations. The present study addresses the magnetic contribution in the atomic driving forces behind the chemical composition in Fe-Cr alloyed with Al, Ti, V, Mn, Co, Ni, and Mo. Using the ab initio exact muffin-tin orbitals method and an Ising-type spin model, it is found that the magnetic moment of the solute atom combined with the ind…

The Origin of Mean-Field Behavior in an Elastic Ising Model

Simple elastic models of spin-crossover compounds are known empirically to exhibit classical critical behavior. We demonstrate how the long-ranged interactions responsible for this behavior arise naturally upon integrating out mechanical fluctuations of such a model. A mean field theory applied to the resulting effective Hamiltonian quantitatively accounts for both thermodynamics and kinetics observed in computer simulations, including a barrier to magnetization reversal that grows extensively with system size. For nanocrystals, which break translational symmetry, a straightforward extension o…

s+if pairing in Ising superconductors

We show that an in-plane Zeeman field applied to non-centrosymmetric Ising superconductors converts singlet $s$-wave Cooper pairs to equal-spin triplet $if$ pairs, leading to an enhancement of the critical transition line beyond expected from Ising spin-orbit coupling. Singlet to triplet conversion relates to a phase transformation due to spin rotation by the Zeeman field and has a geometric origin. The discussion is especially relevant, but not limited to monolayer transition metal dichalcogenides.