Explore the vast range of titles available.

The magneto-optical Kerr effect (MOKE) has been intensively studied in a variety of ferro- and ferrimagnetic materials as a powerful probe for electronic and magnetic properties1–3 and for magneto-optical technologies4. The MOKE can be additionally useful for the investigation of the antiferromagnetic (AF) state, although thus far limited to insulators5–9. Here, we report the first observation of the MOKE in an AF metal. In particular, we find that the non-collinear AF metal Mn3Sn (ref. 10) exhibits a large zero-field Kerr rotation angle of 20 mdeg at room temperature, comparable to ferromagnetic metals. Our first-principles calculations clarify that ferroic ordering of magnetic octupoles11 produces a large MOKE even in its fully compensated AF state. This large MOKE further allows imaging of the magnetic octupole domains and their reversal. The observation of a large MOKE in an AF metal will open new avenues for the study of domain dynamics as well as spintronics using antiferromagnets12–16.

Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g−1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe2O4, MMoO4 and MCo2O4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo2S4, display a high specific capacitance of 1269 F g−1, which is four times higher than those of transition metals oxides, e.g., Zn–Co ferrite, of 296 F g−1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites.

Crystal symmetries may protect single Dirac cones on the surface of a photonic crystal, creating a photonic analogue of a three-dimensional solid-state topological insulator. Topology of electron wavefunctions was first introduced to characterize the quantum Hall states in two dimensions discovered in 1980 (ref.  1 ). Over the past decade, it has been recognized that symmetry plays a crucial role in the classification of topological phases, leading to the broad notion of symmetry-protected topological phases 2 . As a primary example, topological insulators 3 , 4 are distinguished from normal insulators in the presence of time-reversal symmetry ( ). A three-dimensional (3D) topological insulator 3 , 4 , 5 , 6 exhibits an odd number of protected surface Dirac cones, a unique property that cannot be realized in any 2D systems. Importantly, the existence of topological insulators requires Kramers’ degeneracy in spin–orbit coupled electronic materials; this forbids any direct analogue in boson systems 7 . In this report, we discover a 3D topological photonic crystal phase hosting a single surface Dirac cone, which is protected by a crystal symmetry 8 , 9 , 10 —the nonsymmorphic glide reflection 11 , 12 , 13 rather than . Such a gapless surface state is fully robust against random disorder of any type 14 , 15 . This bosonic topological band structure is achieved by applying alternating magnetization to gap out the 3D ‘generalized Dirac points’ discovered in the bulk of our crystal. The Z 2 bulk invariant is characterized through the evolution of Wannier centres 16 . Our proposal—readily realizable using ferrimagnetic materials at microwave frequencies 17 , 18 —expands the scope of 3D topological materials from fermions to bosons.

Ferrimagnetic alloys are model systems for understanding the ultrafast magnetization switching in materials with antiferromagnetically coupled sublattices. Here we investigate the dynamics of the rare-earth and transition-metal sublattices in ferrimagnetic GdFeCo and TbCo dots excited by spin–orbit torques with combined temporal, spatial and elemental resolution. We observe distinct switching regimes in which the magnetizations of the two sublattices either remain synchronized throughout the reversal process or switch following different trajectories in time and space. In the latter case, we observe a transient ferromagnetic state that lasts up to 2 ns. The asynchronous switching of the two magnetizations is ascribed to the master–agent dynamics induced by the spin–orbit torques on the transition-metal and rare-earth sublattices and their weak antiferromagnetic coupling, which depends sensitively on the alloy microstructure. Larger antiferromagnetic exchange leads to faster switching and shorter recovery of the magnetization after a current pulse. Our findings provide insight into the dynamics of ferrimagnets and the design of spintronic devices with fast and uniform switching. Asynchronous sublattice magnetization switching is found in a ferrimagnetic material and understood by considering the exchange coupling and alloy microstructure.

We use the density matrix renormalization group to perform accurate calculations of the ground state of the nearest-neighbor quantum spin S = 1/2 Heisenberg antiferromagnet on the kagome lattice. We study this model on numerous long cylinders with circumferences up to 12 lattice spacings. Through a combination of very-low-energy and small finite-size effects, our results provide strong evidence that, for the infinite two-dimensional system, the ground state of this model is a fully gapped spin liquid.

Spin-orbit torques (SOTs) have been widely understood as an interfacial transfer of spin that is independent of the bulk properties of the magnetic layer. Here, we report that SOTs acting on ferrimagnetic Fe x Tb 1- x layers decrease and vanish upon approaching the magnetic compensation point because the rate of spin transfer to the magnetization becomes much slower than the rate of spin relaxation into the crystal lattice due to spin-orbit scattering. These results indicate that the relative rates of competing spin relaxation processes within magnetic layers play a critical role in determining the strength of SOTs, which provides a unified understanding for the diverse and even seemingly puzzling SOT phenomena in ferromagnetic and compensated systems. Our work indicates that spin-orbit scattering within the magnet should be minimized for efficient SOT devices. We also find that the interfacial spin-mixing conductance of interfaces of ferrimagnetic alloys (such as Fe x Tb 1- x ) is as large as that of 3 d ferromagnets and insensitive to the degree of magnetic compensation. There has been a lot of interest in using antiferromagnets for magnetic memories, due to their fast dynamics, and resilience to stray fields. Such a memory was supposed to be switched by a spin-orbit torque. Here, Zhu and Ralph find that as a ferrimagnet approaches the magnetic compensation point, the spin-orbit torque acting on the ferrimagnet vanishes due to competing spin relaxation processes.

Highly efficient and effective treatments of hazardous dye-based color effluents are a major problem in the industrial sector. In this research, the cobalt ferrite (CoFe2O4) catalyst was produced and used for the degradation of Congo red (CR) as a model dye from aqueous solution. For a said purpose, cobalt ferrite (CoFe2O4) nanostructures with photocatalytic degradation potential were engineered via co-precipitation method using Fe2(SO4)3, CoO2, and triethylene glycol (as a stabilizing agent). As prepared, CoFe2O4 nanostructures were further surface-functionalized with 3-APTES and tested for CR degradation. The prepared CoFe2O4 nanostructures were characterized by X-ray diffraction, Fourier transform infra-red (FT-IR), scanning electron microscopy (SEM), and Brunauer-Emmitt-Teller (BET) analysis. UV-visible absorption was used to measure the optical band gap of prepared CoFe2O4 nanostructures through Tauc plots. The as-prepared CoFe2O4 nanostructure bandgap was found to be 2.71 EV while using an acidic medium. The degradation rates of CR dye for bs-CoFe2O4, as-CoFe2O4, and fs-CoFe2O4 nanostructures at pH 9 were 84, 87, and 92%, respectively. Furthermore, the influences of various process parameters, i.e., the effect of catalyst dose, contact time, dye dose/concentration, pH effect, and effect of different acids, were checked for the prepared three types of nanostructures, i.e., bs-CoFe2O4, as-CoFe2O4, and fs-CoFe2O4. The kinetics models properly explained that the reaction of degradation following pseudo-first-order kinetics.

Control of magnetism on the atomic scale is becoming essential as data storage devices are miniaturized. We show that antiferromagnetic nanostructures, composed of just a few Fe atoms on a surface, exhibit two magnetic states, the Néel states, that are stable for hours at low temperature. For the smallest structures, we observed transitions between Néel states due to quantum tunneling of magnetization. We sensed the magnetic states of the designed structures using spin-polarized tunneling and switched between them electrically with nanosecond speed. Tailoring the properties of neighboring antiferromagnetic nanostructures enables a low-temperature demonstration of dense nonvolatile storage of information.

Nanoscale anti-ferromagnetic (AFM) NiO exhibits intriguing magnetic anomalies influenced by factors such as size, stoichiometry, surface chemistry, and lattice strain. In the present work, black-coloured NiO nanoparticles were synthesized by combustion method, incorporating cationic Ni 2+ vacancies and Ni 3+ species on their surface. Annealing NiO at high temperatures (400–800 °C) led to a colour change from black to green, indicating the transition from a non-stoichiometric to a stoichiometric state. The formation of Ni 2+ vacancies disrupted AFM ordering between Ni 2+ and O 2− ions, while the presence of Ni 3+ promoted double exchange interactions between Ni 3+ and neighbouring Ni 2+ ions, contributing to ferromagnetism (FM) in AFM NiO. The spin exchange interaction at AFM-FM core–shell interface in NiO resulted in an exchange bias effect. Notably, the NiO nanoparticles with smaller average crystallite size (~ 5 nm) and higher cationic Ni 2+ vacancies on the surface exhibited strong ferromagnetism and higher coercivity values. In particular, the as-prepared NiO (N) and N-4 samples showed remarkable improvement in exchange bias field, measuring 2.5 kOe and 2.1 kOe, respectively, due to the reinforced spin-exchange interaction within the FM-AFM core–shell structure of NiO. Graphical Abstract

Magnetism plays a key role in modern technology and stimulates research in several branches of condensed matter physics. Although the theory of classical magnetism is well developed, the demonstration of a widely tunable experimental system has remained an elusive goal. Here, we present the realization of a large-scale simulator for classical magnetism on a triangular lattice by exploiting the particular properties of a quantum system. We use the motional degrees of freedom of atoms trapped in an optical lattice to simulate a large variety of magnetic phases: ferromagnetic, antiferromagnetic, and even frustrated spin configurations. A rich phase diagram is revealed with different types of phase transitions. Our results provide a route to study highly debated phases like spin-liquids as well as the dynamics of quantum phase transitions.