Ground-state Magnetic Properties Research Articles

Tunable magnetism in nitride MXenes: consequences of atomic layer stacking.

We have performed density functional theory (DFT) based calculations to investigate the effects of stacking patterns on the electronic and magnetic properties of several nitride MXenes. MXenes, a relatively new addition to the family of two-dimensional materials, have exhibited fascinating properties in several occasions, primarily due to their compositional flexibility. However, compared to carbide MXenes, nitride MXenes are much less explored. Moreover, the structural aspects of MXenes and the tunability they may offer have not been explored until recently. In this work, we have combined these two less-explored aspects to examine the structure-property relationships in the field of magnetism. We find that in the family of M2NT2 (M = Sc, Ti, V, Cr, Mn; T = O, F) MXenes, the stacking of transition metal planes has a substantial effect on the ground state and finite temperature magnetic properties. We also find that the electronic ground states can be tuned by changing the stacking pattern in these compounds, making the materials appropriate for applications as magnetic devices. Through a detailed analysis, we have connected the unconventional stacking pattern-driven tunability of these compounds with regard to electronic and magnetic properties to the local symmetry, inhomogeneity (or lack of it) of structural parameters, and electronic structures.

An Air-Stable Carbon-Centered Triradical with a Well-Addressable Quartet Ground State.

Organic polyradicals with a high-spin ground state and quantum magnetic properties suitable for spin manipulation are valuable materials for diverse innovative technologies, including quantum devices. However, the typically high reactivity and low stability of conventional polyradicals present a major obstacle to such applications. In this study, a highly stable carbon-centered triradical TR with a quartet ground state and excellent stability (τ1/2 of ∼90 days in air-saturated toluene at room temperature) is achieved, which shows apposite magnetic anisotropy and Zeeman splitting partition with favorable addressability. By virtue of the optimal stability, thorough structural and magnetic characterizations are realized. With X-ray crystallography unambiguously proving the molecular structure, the quartet ground state (ΔED-Q = 0.78 kcal/mol) is confirmed by the SQUID measurements, while the cw- and pulsed EPR techniques offer additional supportive evidence for the high-spin nature. Remarkably, owing to the easily attained magnetic anisotropy, selective excitations between different Zeeman splitting levels are successfully demonstrated with TR in its frozen toluene solution without the requirement for special alignment, which is unprecedented for organic polyradicals. Along with the millisecond spin-lattice relaxation and microsecond coherence time manifested by TR, this triradical is promising for potential coherent spin manipulation applications as a multienergy-level quantum information carrier.

SrCu(OH)3Cl , an isolated equilateral triangle spin S=1/2 model system

We have investigated the magnetic ground state properties of the quantum spin trimer compound strontium hydroxy copper chloride SrCu(OH)3Cl using bulk magnetization, specific heat measurements, nuclear magnetic resonance (NMR), and electron spin resonance (ESR) spectroscopy. SrCu(OH)3Cl consists of layers with isolated Cu2+ triangles and hence provides an opportunity to understand the magnetic ground state of an isolated system of S = 1/2 arranged on an equilateral triangle. Although magnetization measurements do not exhibit a phase transition to a long-range ordered state down to T = 2 K, they reveal the characteristic behavior of isolated trimers with an exchange of J=154 K. The Curie-Weiss behavior changes around 50–80 K, as is also seen in the NMR spin-lattice relaxation rate. In zero magnetic field, our specific heat data establish a second-order phase transition to an antiferromagnetic ground state below T= 1.2 K. We have drawn a magnetic field-temperature (H−T) phase diagram based on the specific heat measurements. The ESR data show divergence of the linewidth at lower temperatures, which precedes the phase transition to an antiferromagnetic long-range ordered state with unconventional critical exponents. The temperature variation of the g-factor further confirms the antiferromagnetic phase transition and reflects the underlying magnetocrystalline anisotropy of the compound. Published by the American Physical Society 2024

Metal–insulator transition and G-type antiferromagnetism in CaNbO[formula omitted] perovskite: Insight from DFT+U study

In this work, we have investigated the ground state electronic and magnetic properties of CaNbO3 perovskite using the density functional theory, along with the Hubbard corrections. The study of structural, electronic, and magnetic properties was carried out using semi-empirical parameters. The structural properties reveal that Nb-O bond lengths are unequal in all directions, and ∠O-Nb-O bond angles are not equal to 90°, which makes NbO6 octahedra distorted. The electronic behavior of the compound, considering the strong correlation effect, shows a metal–insulator transition. The reason for this transition is found to be Jahn–Teller distortion. The stable magnetic state of the compound is obtained to be a G-type antiferromagnetic, using various U values.

The Mott transition in the 5d[formula omitted] compound Ba[formula omitted]NaOsO[formula omitted]: A DFT+DMFT study with PAW spinor projectors

Spin–orbit coupling has been reported to be responsible for the insulating nature of the 5d1 osmate double perovskite Ba2NaOsO6 (BNOO). However, whether spin–orbit coupling indeed drives the metal-to-insulator transition (MIT) in this compound is an open question. In this work we investigate the impact of relativistic effects on the electronic properties of BNOO via density functional theory plus dynamical mean-field theory calculations in the paramagnetic regime, where the insulating phase is experimentally observed. The correlated subspace is modeled with spinor projectors of the projector augmented wave method (PAW) employed in the Vienna Ab Initio Simulation Package (VASP), suitably interfaced with the TRIQS package. The inclusion of PAW spinor projectors in TRIQS enables the treatment of spin–orbit coupling effects fully ab-initio within the dynamical mean-field theory framework. In the present work, we show that spin–orbit coupling, although assisting the MIT in BNOO, is not the main driving force for its gapped spectra, placing this material in the Mott insulator regime. Relativistic effects primarily impact the correlated states’ character, excitations, and magnetic ground-state properties.

Inverse Magnetocaloric Effect in Heusler Ni44.4Mn36.2Sn14.9Cu4.5 Alloy at Low Temperatures

Direct measurements of the magnetocaloric effect were performed in a Heusler Ni44.4Mn36.2Sn14.9Cu4.5 alloy at cryogenic temperatures in magnetic fields up to 10 T. The maximum value of the inverse magnetocaloric effect in a 10 T field was ∆Tad = –2.7 K in the vicinity of the first-order magnetostructural phase transition at T0 = 117 K. Ab initio and Monte Carlo calculations were performed to discuss the effect of Cu doping into a Ni-Mn-Sn compound on the ground-state structural and magnetic properties. It is shown that with increasing Cu content the martensitic transition temperature decreases and the Curie temperature of austenite slightly increases. In general, the calculated transition temperatures and magnetization values correlated well with the experimental ones.

An analysis of magnetic and hysteresis characteristics of a mixed spin Ising-type borophene monolayer

In recent years, borophene has developed into an incredibly promising magnetic material that is essential to many industries including superconductivity and fuel cells. In this paper, using Monte Carlo simulation, the ground-state phase diagrams and magnetic properties of an Ising-type borophene monolayer are explored specifically. The results show that induced by crystal field and exchange coupling, the second-order magnetic phase transitions and the compensation temperature are obtained. Additionally, the multiple compensation temperatures and multi-loop hysteresis characteristics are observed, which are vital in multiple magnetic recording.

Ground state structural, electronic and magnetic properties of Mg-doped LaMnO[formula omitted] perovskite: GGA+U study

The effect of Mg doping on the ground state structural, electronic and magnetic properties has been investigated by means of GGA+U calculations. The inspection of the structure, magnetic moment data and density plots, show that by substituting La by Mg at the La site at a concentration of 0.25, the compound exhibits a Pbnm orthorhombic structure and a half metallic ferromagnetic behaviour with degenerated Mn-eg states. The corresponding average A-site cation radius 〈rA〉 value does not allow metallic-insulator phase transition in the compound. However, by doping Mg on Mn site with the same proportion, the resulting compound shows a Pbnm orthorhombic structure and a half metallic behaviour with degeneracy lifting in Mn-eg states. Our results obtained for LaMn0.75Mg0.25MnO3 agree more with experimental data than those obtained for La0.75Mg0.25MnO3, suggesting that Mg will prefer to substitute at the Mn site due to their close ionic radii.

A Self-Consistent Exact Diagonalization Approach to the Ground State Magnetic Properties of the Meridional [V(ddpd)2]3+ Complex

The present paper presents a thorough study of the ground state magnetic properties of the spin-one mononuclear nanomagnet mer-[V(ddpd)2][PF6]3, with the V3+ center exhibiting a distorted octahedral coordination. The theoretical analysis is based on a multiconfigurational, self-consistent approach that effectively parametrizes the total energy spectrum of the considered coordination complex via exact diagonalization. We provide a comprehensive discussion for the obtained zero-field and field-dependent fine structure of the ground state along with the ensuing crystal field splitting of the 3d orbitals. Furthermore, we report the results for the low-field susceptibility, magnetization and the corresponding reversal dynamics, finding good agreement with the experimental data reported in the literature. The calculations show considerable zero-field splitting and strong field-dependent orbital unquenching underlying the occurrence of a field-induced full profile magnetization reversal barrier.

Meta-GGA SCAN Functional in the Prediction of Ground State Properties of Magnetic Materials: Review of the Current State

In this review, we consider state-of-the-art density functional theory (DFT) investigations of strongly correlated systems performed with the meta-generalized gradient approximation (meta-GGA) strongly constrained and appropriately normed (SCAN) functional during the last five years. The study of such systems in the framework of the DFT is complicated because the well-known exchange–correlation functionals of the local density approximation (LDA) and generalized gradient approximation (GGA) families are not designed for strong correlations. The influence of the exchange–correlation effects beyond classical LDA and GGA are considered in view of the prediction of the ground state structural, magnetic, and electronic properties of the magnetic materials, including pure metals, binary compounds, and multicomponent Heusler alloys. The advantages of SCAN and points to be enhanced are discussed in this review with the aim of reflecting the modern state of computational materials science.

Control of magnetic states and spin interactions in bilayer CrCl3 with strain and electric fields: an ab initio study

Using ab initio density functional theory, we demonstrated the possibility of controlling the magnetic ground-state properties of bilayer CrCl_{3} by means of mechanical strains and electric fields. In principle, we investigated the influence of these two fields on parameters describing the spin Hamiltonian of the system. The obtained results show that biaxial strains change the magnetic ground state between ferromagnetic and antiferromagnetic phases. The mechanical strain also affects the direction and amplitude of the magnetic anisotropy energy (MAE). Importantly, the direction and amplitude of the Dzyaloshinskii–Moriya vectors are also highly tunable under external strain and electric fields. The competition between nearest-neighbor exchange interactions, MAE, and Dzyaloshinskii–Moriya interactions can lead to the stabilization of various exotic spin textures and novel magnetic excitations. The high tunability of magnetic properties by external fields makes bilayer CrCl_{3} a promising candidate for application in the emerging field of two-dimensional quantum spintronics and magnonics.

Antiferromagnetic Ordering in Bowtie and AA‐Stacking Bilayer Trapezoidal Graphene Nanoflakes: A Comparison Study

Herein, a comparative computational study inquiring about ground state magnetic properties of a nanometer‐size bowtie graphene quantum dot with an AA‐stacking bilayer trapezoid counterpart based on the single‐orbital Hubbard model and density functional theory (DFT) is presented. The structures have an antiferromagnetic ground state with a 1‐to‐1 correspondence between the local spin polarizations of the two systems. The tight‐binding energy spectra look different. However, a similar fashion in the energy spectra emerges after considering the Hubbard interaction term. A comparison between the spatial distributions of edge states shows that the wave functions in both structures are sublattice polarized by proposing a specific unit cell in the bilayer case. In addition, the on‐site coulombic repulsion consequence on the rising of magnetization and the size of the local magnetic moment has been considered.

Strong spin frustration and magnetism in kagomé antiferromagnets LnCu3(OH)6Br3 (Ln = Nd, Sm, and Eu)

To study the effects of lanthanide ions on the geometrically frustrated antiferromagnets and their magnetic properties, we grew high-quality single crystals of LnCu3(OH)6Br3 (Ln = Nd, Sm, and Eu) by hydrothermal method and studied their crystal structures and magnetic properties. The refinements of the crystal structure referred to the powder x-ray diffraction data show that LnCu3(OH)6Br3 adopt a Kapellasite-type layer structure, which is isostructural to their chlorine analogue. Magnetic susceptibilities demonstrate that LnCu3(OH)6Br3 have strong antiferromagnetic coupling and a pronounced magnetic frustration effect. Magnetization measurements indicate canted antiferromagnetic ordering of Cu2+ ions around 16 K within the kagomé plane and weak ferromagnetic coupling. Moreover, shoulder-like anomalies in specific heat around 16 K could be a signature of emergent of magnetic ordering. The low-temperature negative magnetization and specific heat of LnCu3(OH)6Br3 (Ln = Nd, Sm, and Eu) indicate that Ln 3+ ions induce more exotic magnetic ground state properties.

Bond-disordered Heisenberg antiferromagnets on a square lattice

The ground-state magnetic properties of bond-disordered spin-1/2 Heisenberg Antiferromagnets on a square lattice are investigated using the Stochastic Series Expansion algorithm. We modify the distribution of the previous work and introduce the normalized standard deviation of the exchange coupling to characterize the magnitude of the disorder. By examining the magnetic properties in various distributions with the normalized standard deviation description, we find that the antiferromagnetism follows the same trend in weak disorder and vanishes at a finite value. And we also analyze the data in perspective of the logarithm of exchange coupling's standard deviation.

Fine Structure and the Huge Zero-Field Splitting in Ni2+ Complexes.

We perform a thorough study of the ground state magnetic properties of nickel-based 3d8 complexes. This includes an in-depth analysis of the contribution of the crystal field, spin exchange and spin-orbit interactions to the ground state magnetic properties. Of particular interest to the current investigation are the presence and occurrence of non-trivial zero-field splitting. The study focuses on the cases of Ni2+ ideal octahedral, trigonal bipyramidal, square planar and tetrahedral geometries. We provide results for the complete energy spectrum, the fine structure related to the ground state and the second set of excited states, low-field magnetic susceptibility and magnetization. In addition, we examine the zero-field fine structure in square pyramidal, trigonal pyramidal and trigonal planar complexes. The obtained results unequivocally show that a moderate or highly coordinated 3d8 complex can neither exhibit spin-orbit-driven large and giant magnetic anisotropy nor a huge zero-field splitting. Moreover, in the trigonal bipyramidal coordination, a fine structure associated to the ground state cannot result from the spin-orbit coupling alone.

Easily exfoliable monolayer of GdTe[formula omitted]: ab initio study

A recently synthesized material GdTe3 has shown very interesting properties like superconductivity and high carrier mobility in its bulk and flake form. Here, we have shown the formation of a monolayer of GdTe3 from its bulk parent material by means of exfoliation. We have also studied magnetic ground state and electronic properties of bulk and two-dimensional (2D) GdTe3, using ab initio calculations. We find both of them to have the same anti-ferromagnetic spin arrangement in their ground state. Our calculations further reveal that both bulk and 2D-GdTe3 are metallic, mainly because of the electronic contribution arising from the Te-atoms. The magnetic ground state does not change on the inclusion of the Hubbard-U parameter, calculated self-consistently to have a value of 5.7 eV for the Gd-f electrons. The spin–orbit coupling (SOC) calculations in 2D-GdTe3, for both U = 0 and 5.7 eV, show that the system prefers an in-plane anti-ferromagnetic ordering and has an easy magnetization axis along the crystallographic a-direction.

Electronic structure studies of Kondo lattice compounds CeRhSn[formula omitted] and CeRuSn[formula omitted]: Comparative study

We report on X-ray photoelectron spectroscopy and ab initio electronic structure investigations of CeRuSn3 and CeRhSn3 and their La counterparts. A combined experimental study and band structure calculations indicate a stable configuration of Ce3+ in the both Ce-based compounds. We also documented that the transition metal Rh or Ru with different number of 4d electrons plays a decisive role in controlling the hybridization strength V between the 4f and conduction electron states, which in turn governs the magnetic ground state properties of these compounds. For CeRuSn3V is ∼1.2 times larger than V of CeRhSn3, which is a reason of stronger Kondo interaction in Ru sample, expressed by larger Kondo temperature TK. On the basis of Schrieffer–Wolff transformation, ab initio calculations, and XPS data, we estimated on-site Jfc coupling constants, which are dependent on Wyckoff position of Ce, and allowed to determine Kondo temperatures, as well as explain nature of the magnetic ground states. The interband hybridization forms a pseudogap in the density of states of CeRuSn3, CeRhSn3 and their La-bearing counterparts at the Fermi level, which could be a reason of Mott variable-range hoping behavior.

Magnetic complexity, magnetodielectric effect and DFT calculations on correlation driven Gd2CoMnO6 insulator

In the family of Re2CoMnO6 manganite double perovskites, in contrast to parent La2CoMnO6 compound, Gd2CoMnO6 exhibits multiple magnetic transitions; ferromagnetic (FM) ordering, TC ∼ 112 K followed by AFM transition, TN ∼ 47 K, Gd spins ordering for T < 10 K and large isothermal entropy changes. A study of DC field-superimposed AC magnetic susceptibility measurements revealed the field-induced magnetic glassy behavior below TC and enhancement of FM correlations above TC. From the analysis of Almeida-Thouless behavior and dynamical power-law fit to frequency dependent AC susceptibility, Gd2CoMnO6 exhibits a volume spin glass-like nature below the freezing temperature, Tf ∼ 117.5 K. The isothermal field-dependent magnetic and dielectric permittivity data and temperature dependent Raman measurements (reported in ref. R. X. Silvaet al., J, Appl. Phys. 114 194,102 (2013)) confirms the spin-phonon coupling induced magnetodielectric effect. Further, the ground-state electronic structure and magnetic properties of Gd2CoMnO6 are investigated using DFT + U formalism with Vienna Ab-initio Simulation Package (VASP) code and predicted the material to be a correlation-driven insulator. The correlation value of the Hubbard U parameter at the 4f-Gd elements changes the stability of the magnetic state from Ferri to FM spin alignment for Ueff ≥ 3 eV and is correlated to the experimentally observed field-induced transformation of the short-range-order FiM/spin-glass-like phase into the long-range ordered FM phase.

First principles investigation of spin-orbit coupling driven magnetism of the 3d−5d double-perovskite (Sr/Ca)2FeIrO6

The interplay of spin-orbit coupling (SOC) with the other energy scales gives rise to various novel and interesting quantum phenomena in the Ir based double perovskites. In recent findings the double-perovskites ${\mathrm{Sr}}_{2}{\mathrm{FeIrO}}_{6}$ (SFIO) and ${\mathrm{Ca}}_{2}{\mathrm{FeIrO}}_{6}$ (CFIO) have been reported to fall under the category of a SOC driven antiferromagnetic (AFM) Mott insulator. Using density functional theory based first principles calculations, we have performed a comparative electronic structure investigation of these compounds. We reveal the microscopic origin of the difference in the AFM transition temperature observed in the experiments through the calculated exchange interactions and the Wannier functions. We addressed the role of SOC in dictating the ground state properties of these two compounds. Although both of the compounds are isoelectronic and isovalent, however, the effective strength and the impact of SOC is very different and nonmonotonic in these compounds, due to the delicate balance with the other energy scales. Our study advances the understanding of the nontrivial role of SOC in driving ground state magnetic properties of the Ir based oxides in general and explores the opportunities for further designing of the SOC driven quantum phases.

Magnetic Properties and Compensation Temperature of a Mixed Monolayer Coronene-Like Nanostructure: Monte Carlo Study

In this study, the ground-state phase diagrams and magnetic properties of mixed spin ([Formula: see text]-1, [Formula: see text]-7/2) of the monolayer coronene-like nanostructure have been investigated using Monte Carlo simulations (MCS) in the frame of the Blume Capel model. In the first part, ground-state phase diagrams have been analyzed in order to show the more stable configurations of spins corresponding to various planes. In addition, MCS is applied to study the behavior of the compensation and blocking temperatures by varying the exchange coupling interaction values. Finally, the hysteresis cycle behaviors have been investigated for selected values of exchange coupling parameters, temperature and crystal field. The theoretical results obtained in this study can enrich the magnetic properties of nanosystems and pave the way for researchers to experimentally study monolayer coronene-like nanostructure for future applications in nanotechnology.