Search Results (281)

Recently, a new class of magnetic material, termed altermagnets, has caught the attention of the magnetism and spintronics community. The magnetic phenomenon arising from these materials differs from traditional ferromagnetism and antiferromagnetism. It generally lacks net magnetization and is characterized by unusual non-relativistic spin-splitting and broken time-reversal symmetry. This leads to novel transport properties, such as the anomalous Hall effect, the crystal Nernst effect, and spin-dependent phenomena. Spin-dependent phenomena such as spin currents, spin-splitter torques, and high-frequency dynamics emerge as key characteristics in altermagnets. This paper reviews the main aspects pertaining to altermagnets by providing an overview of theoretical investigations and experimental realizations. We discuss the most recent developments in altermagnetism and prospects for exploiting its unique properties in next-generation devices. Full article

An altermagnet, characterized by its distinctive magnetic properties, may hold potential applications in diverse fields such as magnetic materials, spintronics, data storage, and quantum computing. As a prototypical altermagnet, RuO₂ exhibits spin polarization and demonstrates the advantageous characteristics of high electrical conductivity and low thermal conductivity. These exceptional properties endow it with considerable promise in the emerging field of thermal spintronics. We studied the electronic structure and thermoelectric properties of RuO₂; the constructed RuO₂/TiO₂/RuO₂ all-antiferromagnetic tunnel junction (AFMTJ) exhibited thermally induced magnetoresistance (TIMR), reaching a maximum TIMR of 1756% at a temperature gradient of 5 K. Compared with prior studies on RuO₂-based antiferromagnetic tunnel junctions, the novelty of this work lies in the thermally induced magnetoresistance based on its superior thermoelectric properties. In parallel structures, the spin-down current dominates the transmission spectrum, whereas in antiparallel structures, the spin-up current governs the transmission spectrum, underscoring the spin-polarized thermal transport. In addition, thermoelectric efficiency emphasizes the potential of RuO₂ to link antiferromagnetic robustness with ferromagnetic spin functionality. These findings promote the development of efficient spintronic devices and spin-based storage technology for waste heat recovery and emphasize the role of spin splitting in zero-magnetization systems. Full article

The new polyoxometalate [Co₇(OH)₆(H₂O)₂(CH₃COO)₄(PW₉O₃₄)₂]¹³⁻ (1) has been synthesized and characterized by IR, UV-Vis-NIR, TGA-TDA, X-ray single crystal analysis, and magnetic studies; 1 consists of two trilacunary heptadentate B-α-[PW₉O₃₄]⁹⁻ ligands encapsulating a heptacobalt dicubane-like {Co^II₆Co^IIIO₈} core, in which the Co²⁺ ions are further coordinated by two water molecules and four acetate anions acting as monodentate ligands. The magnetic properties of 1 have been fitted according to an anisotropic exchange model in the low-temperature regime and discussed on the basis of ferromagnetic interactions between Co²⁺ ions with angles Co–L–Co (L = O, OH) close to orthogonality and weakly antiferromagnetic interactions between Co²⁺ ions connected through a central diamagnetic Co³⁺ ion. Full article

Manganese oxides (manganites) are among the most studied materials in condensed matter physics due to the famous colossal magnetoresistance and very rich phase diagrams characterized by strong competition between ferromagnetic (FM) metallic and antiferromagnetic (AFM) insulating phases. One of the key questions that remains open even after more than thirty years of intensive research is the exact conductivity mechanism in insulating as well as in metallic phases and its relation to the corresponding magnetic structure. In order to shed more light on this problem, here, we report magnetotransport measurements on sintered nanocrystalline samples of the very poorly explored manganites ${\mathrm{Ca}}_{1-x}{\mathrm{Gd}}_x{\mathrm{MnO}}_3$ with $x=0.05$ and $x=0.10$, in the temperature range 2–300 K, and in magnetic fields up to 16 T. Our results indicate that both compounds at low temperatures exhibit metallic behavior with a peculiar resistivity upturn and a large negative magnetoresistance. We argue that such behavior is consistent with a Kondo-like scattering on Gd impurities coupled with the percolation of FM metallic regions within insulating AFM matrix. Full article

Opto-spintronics is an emerging field that focuses on harnessing light to manipulate and analyze electron spins to develop next-generation electronic devices. This paper explores recent progress and the role of solid-state materials in opto-spintronics by focusing on key classes of materials, such as ferromagnetic semiconductors, two-dimensional (2D) transition metal dichalcogenides (TMDCs), and topological insulators. It examines the unique properties of ferromagnetic and antiferromagnetic materials and their ability to interact with light to affect spin dynamics, offering potential for improved sensing and quantum computing. By combining opto-spintronics with solid-state systems, spintronic devices could become faster and more efficient, leading to new technological advancements and scalable technologies. Full article

The structural, electronic, and magnetic properties of bismuth ferrite (BiFeO₃) and Bi₂Fe₄O₉ nanostructures were investigated using Density Functional Theory (DFT) within the Generalized Gradient Approximation (PBE-GGA) plus U approach. The PBE-GGA + U calculations predict band gaps of 2.4 eV for BiFeO₃ and 2.3 eV for Bi₂Fe₄O₉, closely aligning with experimental data. The analysis of partial and total density of states reveals strong hybridization between iron 3d and oxygen 2p states, with a significant contribution from Fe 3d orbitals in both structures. Additionally, nanostructure and crystal symmetry are crucial in influencing the magnetic properties of BiFeO₃ and Bi₂Fe₄O₉. Our calculations indicate that the antiferromagnetic phase is energetically more favorable than the ferromagnetic phase in both materials. Full article

Quantum batteries represent a new and promising technological application of quantum mechanics, offering the potential for enhanced energy storage and fast charging. In this work, we study a quantum battery composed of three two-level systems with XXZ coupling operating under open boundary conditions. We investigate the role played by ferromagnetic and antiferromagnetic initial configurations on the charging dynamics of the battery. Two charging mechanisms are explored: static charging, where the battery interacts with a constant classical external field, and harmonic charging, where the field oscillates periodically over time. Our results demonstrate that static charging can be more efficient in the ferromagnetic case, achieving maximum energy due to complete population inversion between the ground and excited states. In contrast, harmonic charging excels in the antiferromagnetic case. By analyzing the stored energy and the average charging power in these two regimes, we highlight the impact of anisotropy on the performance of quantum batteries. Our findings provide valuable insights for optimizing quantum battery performance based on the system’s initial state and coupling configuration, paving the way for the study of more efficient quantum devices for energy storage. Full article

Organometallic rare-earth complexes have attracted considerable attention in recent years due to their unique structures and exceptional magnetic properties. In this study, we report the synthesis and magnetic characteristics of a family of monopentamethylcyclopentadienyl-coordinated trinuclear rare-earth hepta-chloride clusters [(Li(THF)(Et₂O))(Cp^*RE)₃(μ-Cl)₄(μ₃-Cl)₂(μ₄-Cl)] (RE₃: RE =Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Cp* = pentamethylcyclopentadienide). These clusters were synthesized by reacting LiCp* with RECl₃ in a 1:1 molar ratio within a mixed solvent system (THF: Et₂O = 1:9), resulting in high solubility in common organic solvents such as DCM, THF, and Et₂O. Magnetic studies conducted on these paramagnetic clusters reveal the coexistence of ferromagnetic and antiferromagnetic superexchange interactions in Gd₃. Additionally, Dy₃ exhibits both ferromagnetic and antiferromagnetic intramolecular dipolar interactions. Notably, slow magnetic relaxation was observed in Dy₃ below 23 K under a zero DC applied field with an energy barrier of 125(6) cm⁻¹. Full article

We investigate the coupled-top model, which describes two large spins interacting along both x and y directions. By tuning coupling strengths along distinct directions, the system exhibits different symmetries, ranging from a discrete $Z_2$ to a continuous U(1) symmetry. The anisotropic coupled-top model displays a discrete $Z_2$ symmetry, and the symmetry breaking induced by strong coupling drives a quantum phase transition from a disordered paramagnetic phase to an ordered ferromagnetic or antiferromagnetic phase. In particular, the isotropic coupled-top model possesses a continuous U(1) symmetry, whose breaking gives rise to the Goldstone mode. The phase boundary can be well captured by the mean-field approach, characterized by the distinct behaviors of the order parameter. Higher-order quantum effects beyond the mean-field contribution can be achieved by mapping the large spins to bosonic operators via the Holstein–Primakoff transformation. For the anisotropic coupled-top model with $Z_2$ symmetry, the energy gap closes, and both quantum fluctuations and entanglement entropy diverge near the critical point, signaling the onset of second-order quantum phase transitions. Strikingly, when U(1) symmetry is broken, the energy gap vanishes beyond the critical point, yielding a novel critical exponent of 1, rather than $1/2$ for $Z_2$ symmetry breaking. The rich symmetry structure of the coupled-top model underpins its role as a paradigmatic model for studying quantum phase transitions and exploring associated physical phenomena. Full article

The reaction of CuCl₂∙2H₂O, (E)-2-hydroxy-1,2-di(pyridin-2-yl)ethanone oxime (α-pyroxH₂) and Et₃N in refluxing MeOH gave complex [Cu₁₂Cl₁₂(mpydol)₄(pydox)₂(MeOH)₄] (1), where mpydol²⁻ is the dianion of 1,2-dimethoxy-1,2-di(pyridin-2-yl)ethane-1,2-diol and pydox²⁻ is the dianion of (E,E)-1,2-di(pyridin-2-yl)ethanedione dioxime. “Blind” experiments have proven that the transformation of α-pyroxH₂ is copper(II)-assisted. By changing the solvent from MeOH to MeCN, the polymeric compound {[Cu₄Cl₄(pic)₄]}_n (2) was isolated; pic⁻ is the pyridine-2-carboxylato(-1) ligand. The observed α-pyroxH₂ → pic⁻ transformation is also copper(II)-assisted. The topology of the metal ions in 1 can be described as consisting of four consecutive isosceles triangles in a zigzag configuration. Complex 2 is a 2D coordination polymer consisting of Cu^II₄ squares. Complete mechanistic views for the α-pyroxH₂ → mpydol²⁻, pydox²⁻ and pic⁻ transformations are critically discussed. In 1, the six Cu^II ions of the “central” triangles seem to be strongly antiferromagnetically coupled, thus cancelling out their spins ($S_{{\mathrm{Cu}}_6}$ = 0). The two local spins of S = 1/2 for each of the antiferromagnetically coupled “terminal” Cu^II₃ triangles result in an overall S = 1 ground state spin value for 1. In 2, the four Cu^II ions within each tetrameric unit are practically isolated and ferromagnetic interactions occur between these units through Cu^II–(μ-Cl)–Cu^II bridges. Full article

Basic principles of ferroelectric activity induced by the noncollinear alignment of spins are reviewed. There is a fundamental reason why the inversion symmetry can be broken by certain magnetic order. This situation occurs when the magnetic order simultaneously involves ferromagnetic ($\mathit{F}$) and antiferromagnetic ($\mathit{A}$) counterparts, transforming under the spatial inversion $\mathcal{I}$ and time reversal $\mathcal{T}$ as $\mathcal{I}\mathit{F}=\mathit{F}$ and $\mathcal{IT}\mathit{A}=\mathit{A}$, respectively. The incompatibility of these two conditions results in breaking the inversion symmetry, which manifests itself in the electric polarization $\overrightarrow{P}$. The noncollinear alignment of spins is one of examples of such coexistence of $\mathit{F}$ and $\mathit{A}$. This coexistence principle imposes a constraint on possible dependencies of $\overrightarrow{P}$ on the directions of spins, which can include only “antisymmetric coupling” in the bond, ${\overrightarrow{\mathcal{P}}}_{ij}·[{\mathit{e}}_i\times {\mathit{e}}_j]$, and “single-ion anisotropy”, ${\mathit{e}}_i·$ $\overrightarrow{\mathbb{\Pi }}$ ${\mathit{e}}_i$. Microscopically, ${\overrightarrow{\mathcal{P}}}_{ij}$ can be evaluated in the framework of superexchange theory. For the single Kramers doublet, this theory yields ${\overrightarrow{\mathcal{P}}}_{ij}\sim {\overrightarrow{\mathit{r}}}_{ij}^{\phantom{0}}$, where ${\overrightarrow{\mathit{r}}}_{ij}^{\phantom{0}}$ is the spin-dependent part of the position operator induced by the relativistic spin-orbit coupling. ${\overrightarrow{\mathit{r}}}_{ij}^{\phantom{0}}$ remains invariant under spatial inversion, providing the microscopic reason why noncollinear alignment of spins can induce $\overrightarrow{P}$ even in centrosymmetric crystals. The symmetry properties of ${\overrightarrow{\mathit{r}}}_{ij}^{\phantom{0}}$ can be rationalized from the viewpoint of symmetry of Kramers states. Particularly, the commonly used Katsura–Nagaosa–Balatsky (KNB) rule $\overrightarrow{P}\propto {\overrightarrow{ϵ}}_{ji}\times [{\mathit{e}}_i\times {\mathit{e}}_j]$ (${\overrightarrow{ϵ}}_{ji}$ being the direction of the bond $ij$) can be justified only for relatively high symmetry of the bonds. The single-ion anisotropy vanishes for the spin ${\displaystyle \frac{1}{2}}$ or if magnetic ions are located in inversion centers, thus severely restricting the applicability of this microscopic mechanism. The properties of multiferroic materials are reconsidered from the viewpoint of these principles. A particular attention is paid to complications caused by possible deviations from the KNB rule. Full article

Here, we report the hydrothermal synthesis of BFO (bismuth ferrite) and Bi_1−xAg_xFeO₃ (x = 0.01, 0.02) ultrafine nanopowders. The diffraction patterns show that all obtained particles belong to the R3c space group. On top of that, crystal structure prediction has been accomplished using bond valence calculations (BVCs). Several promising perovskite structures have been proposed together with experimentally observed modifications of BFO as a function of silver doping. Magnetization measurements were performed on BFO, both pure and substituted with 1% and 2% of Ag. The addition of Ag in BFO did not affect the Neel temperature, T_N = 630 K for all samples; instead, the influence of Ag was observed in the increase in the value and irreversibility of magnetization, which are usual characteristics of weak ferromagnetism. Our calculations based on density functional theory (DFT) are in agreement with the experimental finding of enhanced magnetization upon Ag doping of antiferromagnetic BFO, which is assigned to the perturbation of magnetic-type interactions between Fe atoms by Ag substitutional doping. Additionally, electronic and magnetic properties were studied for all phases predicted by the BVCs study. DFT predicted half-metallicity in the γ phase of BFO, which may be of great interest for further study and potential applications. Full article

Four similar dinuclear lanthanide complexes have been synthesized by linking two [Ln(hfac)_2–3] units (hfac stands for hexafluoroacetylacetone) with different μ-O bridging ligands. The 2,2′-bipyridine-N-oxide ligand (bmpo) constructed two centrosymmetric complexes [Ln₂(hfac)₆(bmpo)₂] (Ln = Dy(1), Tb(2)), with nine-coordinated Ln^III ions showing C_s low symmetry, while the ligand di(2-pyridyl)methanediol (py₂C(OH)₂) formed another two compounds [Ln₂(hfac)₄(py₂C(OH)O)₂] (Ln = Dy(3), Tb(4)), with two kinds of eight-coordinated Ln^III ions exhibiting improved symmetries of D_4d and D_2d. Magnetic analysis reveals that Dy₂ complex 1 shows intramolecular antiferromagnetic coupling (J = −1.07 cm⁻¹) and no relaxation process above 2.0 K even in a 1000 Oe dc field, owing to the low symmetry of Dy^III ions, while the similar Dy₂ complex 3 with improved Dy^III symmetry shows ferromagnetic coupling (J = 1.17 cm⁻¹), which induces a 1000 Oe dc field-induced two-step magnetization relaxation processes with effective energy barrier U_eff = 47.4 K and 25.2 K for the slow relaxation and fast relaxation processes, respectively. This study proves again that the improved symmetry combined with intramolecular ferromagnetic interactions, both mediated by bridging ligands, can enhance the Dy^III anisotropy, further quench the quantum tunneling of the magnetization, and finally, enhance the magnetic behavior of Ln^III-based systems. Full article

Exchange-biased specimens were produced by molecular beam epitaxy (MBE) of ferromagnetic (FM) Co-on-CoO substrates after the substrates had been irradiated by heavy ions to induce defects in the antiferromagnet (AFM). Measurements were obtained at different temperatures for different sample orientations with respect to the external magnetic field. While the EB was relatively small, measurements of the bulk magnetization at low temperatures revealed unusually shaped hysteresis loops. The surface magnetization, however, showed simple, nearly rectangular hysteresis loops. This study focuses on the advantage of complementary information on surface and bulk magnetization from optical and non-optical measurement methods. Full article

Redox-induced magnetic regulation in organic diradicals is distinctly attractive. In this work, taking nitroxide radicals as spin sources, we predict the magnetic properties of 9, 10-anthraquinone, 9, 10-phenaquone, 9, 10-diazanthracene and 9, 10-diazepine-bridged molecular diradical structures in which the couplers are prone to dihydrogenation reduction at positions 9 and 10. As evidenced at both the B3LYP and M06-2X levels of theory, the calculations confirm that the magnetic transitions between ferromagnetism and antiferromagnetism can take place for 9, 10-anthraquinone and 9, 10-diazanthracene-bridged diradicals after dihydrogenation. The differences in the magnetic behaviors and magnetic magnitudes of 9, 10-anthraquinone and 9, 10-diazanthracene-bridged diradicals before and after dihydrogenation could be attributed to their noticeably different spin-interacting pathways. As for 9, 10-phenaquone and 9, 10-diazepine-bridged diradicals, the calculated results indicate that the signs of their magnetic exchange coupling constants J do not change, but the magnitudes remarkably change after dihydrogenation. The connecting bond character and spin polarization are crucial in explaining the different magnetic magnitudes of these designed diradicals. In detail, shorter bonds and larger spin polarization are responsible for strong magnetic coupling. In addition, the diradical with an extensively π-conjugated structure can effectively promote magnetic coupling. The McConnell’s spin alternation rule is the key to understanding the observed ferromagnetism and antiferromagnetism of these diradicals. The work provides useful information for the rational design of redox-regulated magnetic molecular switches. Full article