Ferromagnetic Order Research Articles

Influence of an ultrathin Mn ‘spy layer’ on the static and dynamic magnetic coupling within FePt/NiFe bilayers

Abstract We explore whether insertion of an ultrathin Mn ‘spy layer’ within a magnetic hard/soft bilayer can enable depth-sensitive element-specific measurements of the static and dynamic magnetization, while avoiding significant disruption of the original magnetic state. MgO(110)/FePt(100 Å)/NiFe(200 Å)/Mn(tMn Å)/NiFe(200 Å) samples with Mn thicknesses of tMn=0, 5, and 10Å were fabricated by magnetron sputtering and studied by element-selective x-ray magnetic circular dichroism (XMCD), vector network analyzer ferromagnetic resonance (VNA-FMR), and x-ray detected ferromagnetic resonance (XFMR). For tMn= 5 Å, the magnetic reversal properties remain broadly similar to tMn= 0 Å. For tMn=10 Å, the two NiFe layers decouple with XMCD hysteresis loops at the Mn edge showing two switching events that suggest the presence of two distinct Mn-containing regions. While the Mn moments within each region have ferromagnetic order, their relative alignment is antiparallel at high field. Analysis of the magnetic data and additional scanning transmission electron microscopy (STEM) measurements point to the presence of a Mn layer at the lower NiFe/Mn interface, and the formation of a NiFeMn alloy at the upper Mn/NiFe interface. The Mn moments of the former region lie antiparallel to those of the underlying NiFe layer. The VNA-FMR data suggests that for tMn= 5 and 10 Å, the interfacial exchange coupling at the FePt/NiFe is suppressed and the in-plane uniaxial magnetic anisotropy of the NiFe is increased, perhaps due to migration of Mn towards the buried interface. The above findings show that Mn is a problematic magnetic spy, and that a Mn thickness of less than 5Å would be required.

Defect-Selective Ferromagnetic Ordering and Optical Tunability in C Ion-Implanted Microflowers Composed of TiO2 Nanorods

Defect-Selective Ferromagnetic Ordering and Optical Tunability in C Ion-Implanted Microflowers Composed of TiO₂ Nanorods

Anion Exchange and Lateral Heterostructure Formation in Ferromagnetic PEA2Cr(Cl,Br)4 Two-Dimensional Perovskites.

Postsynthetic vapor-phase anion exchange in the ferromagnetic two-dimensional (2D) hybrid metal-halide perovskite, PEA2CrCl4 (PEA+ = phenethylammonium), is reported. Anion exchange using vaporous trimethylsilyl bromide (TMS-Br) is shown to drive complete conversion of solution-processed PEA2CrCl4 polycrystalline thin films to PEA2CrBr4. Low-temperature magnetic circular dichroism spectroscopy indicates ferromagnetic ordering in these PEA2CrCl4 and PEA2CrBr4 films. Via partial anion exchange of exfoliated flakes of PEA2CrCl4 single crystals, we demonstrate that it is possible to generate abrupt lateral PEA2CrCl4/PEA2CrBr4 magneto-heterointerfaces. Kinetic studies reveal that lateral heterostructure formation is dictated by rapid edge-site halide exchange followed by slower intralayer bromide diffusion, and there is negligible interlayer (3D) bromide or TMS-Br diffusion. The importance of the bulky PEA+ interlayer cation in suppressing 3D diffusion is highlighted by parallel anion-exchange experiments on MA2CrCl4 (MA+ = methylammonium), which instead show 3D exchange. Comparison of anion-exchange reactions in PEA2CrCl4, PEA2MnCl4, and PEA2PbCl4 shows that 2D bromide diffusion is slowest in PEA2CrCl4, attributed to the antiferrodistortive ordering found in this composition. In addition to demonstrating both postsynthetic composition control and heterostructure formation in ferromagnetic Cr-based 2D perovskites for the first time, these results also advance our fundamental understanding of ion-exchange processes in this relatively unexplored family of 2D perovskites, broadening opportunities for investigation and control of novel spin effects in low-dimensional metal-halide perovskites.

Disclosing the magnetic ground state of PrBaMn2O6

In this work, we report a neutron diffraction study on a single crystal of the layered PrBaMn2O6 perovskite. This compound undergoes two consecutive magnetic transitions with decreasing temperature. At TC ≈ 309 K, a long-range ferromagnetic ordering is established with the Mn magnetic moments oriented along the c axis. Below TN ≈ 240 K, a spin reorientation gives rise to a sudden decrease of the magnetization and the formation of an antiferromagnetic order. This magnetic transition is also accompanied by an electronic localization caused by a structural phase transition from a high-temperature tetragonal phase (P4/mmm) into a low-temperature orthorhombic one (P21am). Our neutron diffraction study at 12 K has unambiguously identified that the ground magnetic structure for this compound is a layered antiferromagnetic structure along the c axis with the Mn moments oriented in the ab plane along one diagonal of the primitive tetragonal cell. No sign of magnetic scattering associated to a CE-type magnetic structure was found in our study, discarding its occurrence in this compound. This result excludes the occurrence of a charge order transition to account for the electronic localization and it is fully consistent with previous structural studies showing a unique crystallographic site for Mn atom in the low-temperature phase. A symmetry analysis was carried out to identify the magnetic space group of the ferromagnetic order above TN and the two possible groups for the antiferromagnetic ordering below TN.

A first-principle study on the two dimensional Janus MXene TaFeC with spin gapless behaviour

Based on density functional theory calculations, we have investigated the two-dimensional Janus MXene TaFeC, focusing particularly on the magnetic and electronic properties. It is found TaFeC is dynamically, mechanically, and thermodynamically stable. With both sizable Curie temperature and enhanced out-off plane magneto-crystalline anisotropy energy, the Janus MXene TaFeC has the potential to be applied at finite temperature. The mechanism behind the magneto-crystalline anisotropy energy and magnetism are explained based on perturbation theory and crystal field splitting, respectively. Under biaxial strain, the ferromagnetic order is robust stable. With a various of effective potential on Fe, the electronic structure evolution is studied, where the effective potential of 1.3 eV is a special case. In such case, the Janus MXene TaFeC can be classified as a new type of spin-gapless semiconductor beyond the previous classifications, behaving topological nontrivial edge states.

A Spin‐Polarized Electron‐Induced MXene‐KBi0.9Co0.1Fe2O5 Photocatalyst for Enhanced Dye Degradation

In photocatalysts aimed to degrade environmental pollutants, photons are generally used as primary stimuli to generate electron–hole pairs to target the chemical bonds to disintegrate. Recently, electron spin has been reported as an essential degree of freedom to improve the performance of photocatalysts. In this work, spin‐polarized electrons and holes are introduced into a brownmillerite KBi0.9Co0.1Fe2O5 semiconductor and a two‐dimensional (2D) MXene composite system by application of an external magnetic field. The spin polarization properties are monitored by measuring the magnetoresistance effect of the MXene‐KBCFO device, which is related to the carrier transfer efficiency. Remarkably, the photocatalytic performance of MXene‐KBCFO is significantly enhanced by the simultaneous application of an external magnetic field and illumination due to the increased number of spin‐polarized photoexcited carriers caused by the synergy effect of the 2D MXene heterostructure together with the ferromagnetic spin ordering. This results in increased reaction hotspots, effective built‐in electric field, extended carrier lifetime, and reduced charge recombination owing to parallel alignment of electron spin orientation. The results show that the efficiency and stability of photocatalytic dye degradation can be effectively enhanced by manipulating the spin‐polarized electrons in the MXene‐based oxide‐perovskite heterostructure photocatalyst.

Interplay of Na Substitution in Magnetic Interaction and Photocatalytic Properties of Ca1-xNaxTi0.5Ta0.5O3 Perovskite Nanoparticles.

This research paper delves into the enhancement of wastewater treatment through the design and synthesis of advanced photocatalytic materials, focusing on the effects of sodium (Na) substitution in Ca1-xNaxTa0.5Ti0.5O3 perovskites. By employing various analytical techniques such as X-ray diffraction, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy and UV-vis spectroscopy, the study examines the transition of these perovskites from tetragonal to orthorhombic structures and observes a reduction in Ca content with Na substitution, which also favors the cubic phase formation and inhibits secondary phases. Significantly, magnetic property analysis uncovers an unexpected ferromagnetic ordering in these perovskites, including compositions traditionally viewed as non-magnetic. The photocatalytic tests reveal a significant improvement in degrading Rhodamine B dye under visible light, particularly in samples with higher Na levels, attributed to enhanced light absorption and efficient electron processes. The study highlights the optimal Na substitution level for peak photocatalytic performance, offering valuable insights into the complex interplay between structural, magnetic, and photocatalytic properties of these perovskites, and their potential in various applications, thereby contributing to the advancement of wastewater treatment technologies.

Green-synthesized BiFeO3 nanoparticles for efficient photocatalytic degradation of organic dyes, antibiotic and catalytic reduction of 4-nitrophenol

Green-synthesized nanoparticles have recently emerged as promising catalysts for the removal of toxic dyes from water bodies. In this article, Bismuth ferrite (BiFeO3) nanoparticles were synthesized by a simple and low-cost method using Couroupita guianensis plant leaf extract. The particles were used as photocatalysts for degrading RhB, MO dyes, and TC antibiotics, as well as for reducing toxic 4-NP to useful 4-AP. The synthesized nanoparticles were characterized using several state-of-the-art tools. The formation of perovskite structure and the presence of biomolecules on the surface of BiFeO3 nanoparticles was confirmed by FTIR analysis. Raman spectrum revealed a rhombohedral structure of BiFeO3 nanoparticles, corroborating the XRD analysis. FESEM micrograph demonstrated irregularly shaped agglomerated nanoparticles. The average hydrodynamic diameter was estimated to be 51 nm using the DLS technique. The optical energy bandgap of the bismuth ferrite was estimated using Tauc’s relation for direct bandgap semiconductors. SQUID measurements revealed that these nanoparticles exhibit a weak ferromagnetic ordering. Furthermore, these nanomaterials degraded the cationic and anionic dyes effectively because of the formation of hydroxyl radicals, confirmed by the scavenger test. The photocatalytic degradation pathway of RhB dye was investigated through LC-MS analysis, and the intermediate degradation products were identified. The prepared material also exhibited excellent catalytic efficiency in a short duration of time. This study proclaims that these nanoparticles can be used as potential catalysts for the purification of water.

Proximity-induced ferromagnetism of platinum thin film on magnetic insulating CrI3 nanoflakes

The induced magnetization of Pt holds significant promise for the development of spintronic devices. In this study, we constructed a two-dimensional heterostructure consisting of a ferromagnetic insulating CrI3 nanoflake and metallic Pt thin films. The observation of anomalous Hall effect suggests the emergence of a ferromagnetic long-range order in the Pt thin film induced by the magnetic proximity effect. Density functional theory calculations were performed to investigate the underlying mechanisms. We propose that the spontaneous magnetization of Pt in Pt/CrI3 stems from an intensified exchange interaction between Pt 5d and Cr 3d electrons, which is facilitated by the interface coupling and the formation of interfacial hybrid orbitals. These results contribute to a deeper understanding of spin-based phenomena and have potential implications for advancements in the field of spintronics.

Proflavine binding to La-Sr perovskite manganite nanoparticles at temperatures above and below the Сurie temperature

The magnetic properties of La1-xSrxMnO3 (LSMO) nanoparticles within the ferromagnetic region (x ≈ 0.2–0.5) enable their application in two types of cancer treatment: chemotherapy drug delivery and self-controlled hyperthermia. Single-phase La0.80Sr0.20MnO3 nanoparticles were prepared by the sol-gel process followed by mechanical processing. Sample characterization was performed by using XRD, TEM, EPR, and DLS techniques. The encapsulation efficiency of proflavine to the nanoparticles was determined via spectrophotometry. The mean size of crystallites of LSMO nanoparticles is 18 nm, and the Curie temperature is 319 K. Bare LSMO particles do not form a colloidally stable aqueous suspension; they exhibit a zeta potential close to zero and provide micro-sized aggregates. Application of sodium citrate for their stabilization leads to a decrease in the size of agglomerates and to a highly negative zeta potential of –33 mV. The efficiency of proflavine sorption by LSMO nanoparticles increases significantly above the Curie temperature, from 16.1 % at 298 K to 26.2 % at 333 K. This increase is attributed to the partial disruption of nanoparticle agglomerates in suspension after the LSMO phase loses its ferromagnetic order. In summary, heating LSMO nanoparticles above the Curie temperature increases the degree of drug loading on the nanoparticles.

Ferromagnetic quantum critical point protected by nonsymmorphic symmetry in a Kondo metal

Quantum critical points (QCPs), zero-temperature phase transitions, are windows to fundamental quantum-mechanical phenomena associated with universal behaviour. Magnetic QCPs have been extensively investigated in the vicinity of antiferromagnetic order. However, QCPs are rare in metallic ferromagnets due to the coupling of the order parameter to electronic soft modes. Recently, antisymmetric spin-orbit coupling in noncentrosymmetric systems was suggested to protect ferromagnetic QCPs. Nonetheless, multiple centrosymmetric materials host FM QCPs, suggesting a more general mechanism behind their protection. In this context, CeSi2-δ, a dense Kondo lattice crystallising in a centrosymmetric structure, exhibits ferromagnetic order when Si is replaced with Ag. We report that the Ag-substitution to CeSi1.97 linearly suppresses the ferromagnetic order towards a QCP, accompanied by concurrent strange-metal behaviour. Herein, we suggest that, despite the centrosymmetric structure, spin-orbit coupling arising from the local noncentrosymmetric structure, in combination with nonsymmorphic symmetry, can protect ferromagnetic QCPs. Our findings offer a general guideline for discovering new ferromagnetic QCPs and highlight one new family of materials within which the interplay of topology and quantum phase transitions can be investigated in the context of strongly correlated systems.

Theoretical investigation of [formula omitted]-type doping modulated interlayer magnetic and potential topological phases transition in MnSb[formula omitted]Te[formula omitted] based systems

MnSb2Te4, as an important member of intrinsic magnetic topological insulator MnBi2Te4 family, shows promise for realizing quantum anomalous Hall effect (QAHE). However, interlayer A-type antiferromagnetic coupling has been a challenge to successfully observe this novel physical phenomenon in MnSb2Te4 system. Based on density functional theory, our calculations demonstrated that doping p-type non-magnetic elements into 2 SLs and 3 SLs of MnSb2Te4 can induce a magnetic phase transition from interlayer antiferromagnetic to ferromagnetic states with a Curie temperature up to 52.2 K. Moreover, our calculations present that interlayer ferromagnetic coupling and band gap in Ca-doped 2 SLs MnSb2Te4 systems can be further tuned by applying compressive strain. In addition, the interlayer ferromagnetic coupling in MnSb2Te4/Sb2Te3/MnSb2Te4 sandwich heterostructure by p-type doping can be enhanced, The detailed electronic structure analysis show that realization of interlayer ferromagnetic coupling is mainly related to a redistribution of d-electron orbital occupancy in Mn atoms of various SL layers. These findings not only advance the understanding of interlayer ferromagnetic order in ultrathin MnSb2Te4 layers, but also provide new way to realize the QAHE in MnSb2Te4 based systems without introducing extraneous magnetic disorder.

SYNTHESIS OF NANOSIZED PHASES WITH A GARNET STRUCTURE USING SUPERCRITICAL СО2 FLUID

A method was developed for the production of nanosized complex oxides and oxysulfides. The first stage uses supercritical СО2 fluid (SAS – supercritical antisolvent method). This approach makes it possible to obtain precursor-free complex oxides in a narrow nanoscale range. Nanosized rare-earth iron garnets with the general formula R3Fe5O12, where R is a rare earth element, were obtained and studied by physicochemical methods. The resulting samples have a size of less than 100 nm, exhibit ferromagnetic ordering, and can be used as soft magnetic materials. The multi-stage method for the preparation of complex oxysulfides was not previously demonstrated anywhere in the literature. The method involves three stages. At the first stage, a nanosized X-ray amorphous solid solution of the original salts is obtained using the SAS method. Then a nanosized X-ray amorphous component – the oxide phase – is obtained by annealing in a furnace. After this, the resulting oxide phase is mixed with the disulfide of a transition element (Nb, Mo), and high-temperature annealing is performed in an evacuated quartz ampoule. As a result, compact and nanosized phases of the composition Eu3Fe5-3/2xMox□1/2xO12-2xS2x and Eu3Fe5-3/2xNbx□1/2xO12-2xS2x, where x = 0.15, were obtained for the first time. The introduction of the sulfide component, namely NbS2, into the garnet structure increases its magnetic parameters by the factor of 1.5.

The impact of mechanical strain on magnetic and structural properties of 2D materials: A Monte Carlo study.

The inherent flexibility of two-dimensional (2D) materials allows for efficient manipulation of their physical properties through strain application, which is essential for the development of advanced nanoscale devices. This study aimed to understand the impact of mechanical strain on the magnetic properties of two-dimensional (2D) materials using Monte Carlo simulations. The effects of several strain states on the magnetic properties were investigated using the Lennard-Jones potential and bond length-dependent exchange interactions. The key parameters analyzed include the Lindemann coefficient, radial distribution function, and magnetization in relation to temperature and magnetic field. The results indicate that applying biaxial tensile strain generally reduces the critical temperature (Tc). In contrast, the biaxial compressive strain increased Tc within the elastic range, but decreased at higher strain levels. Both compressive and tensile strains significantly influence the ferromagnetic properties and structural ordering, as evidenced by magnetization hysteresis. Notably, pure shear strain did not induce disorder, leaving the magnetization unaffected. In addition, our findings suggest the potential of domain-formation mechanisms. This study provides comprehensive insights into the influence of mechanical strain on the magnetic behavior and structural integrity of 2D materials, offering valuable guidance for future research and advanced material design applications.

Twist-Controlled Ferroelectricity and Emergent Multiferroicity in WSe2 Bilayers.

Recently, researchers have been investigating artificial ferroelectricity, which arises when inversion symmetry is broken in certain R-stacked, i.e., zero-degree twisted, van der Waals (vdW) bilayers. Here, the study reports the twist-controlled ferroelectricity in tungsten diselenide (WSe2) bilayers. The findings show noticeable room temperature ferroelectricity that decreases with twist angle within the range 0° < θ < 3°, and disappears completely for θ ≥ 4°. This variation aligns with moiré length scale-controlled ferroelectric dynamics (0° < θ < 3°), while loss beyond 4° may relate to twist-controlled commensurate to non-commensurate transitions. This twist-controlled ferroelectricity serves as a spectroscopic tool for detecting transitions between commensurate and incommensurate moiré patterns. At 5.5 K, 3° twisted WSe2 exhibits ferroelectric and correlation-driven ferromagnetic ordering, indicating twist-controlled multiferroic behavior. The study offers insights into twist-controlled coexisting ferro-ordering and serves as valuable spectroscopic tools.

Study of the Influence of Ferromagnetic Impurity Concentration on Magnetic Properties of Binary Palladium–Cobalt Alloy

A comparative study of the magnetic properties of a palladium–cobalt alloy with an impurity content of up to 0.05 at. % was made using calculations based on the density functional theory and experimental methods. It was found that the alloys had ferromagnetic ordering, which depended on the impurity concentration. At very low concentrations, less than 1 at. %, the magnetic moment per impurity atom can reach 25 µB.

Magnetic coupled electronic landscape in bilayer-distorted titanium-based kagome metals

Quantum materials whose atoms are arranged on a lattice of corner-sharing triangles, i.e., the kagome lattice, have recently emerged as a captivating platform for investigating exotic correlated and topological electronic phenomena. Here, we combine ultralow temperature angle-resolved photoemission spectroscopy (ARPES) with scanning tunneling microscopy and density functional theory calculations to reveal the fascinating electronic structure of the bilayer-distorted kagome material LnTi3Bi4, where stands for Nd and Yb. Distinct from other kagome materials, LnTi3Bi4 exhibits twofold, rather than sixfold, symmetries, stemming from the distorted kagome lattice, which leads to a unique electronic structure. Combining experiment and theory we map out the electronic structure and discover double flat bands as well as multiple Van Hove singularities (VHSs), with one VHS exhibiting higher-order characteristics near the Fermi level. Notably, in the magnetic version NdTi3Bi4, the ultralow base temperature ARPES measurements unveil an unconventional band splitting in the band dispersions which is induced by the ferromagnetic ordering. These findings reveal the potential of bilayer-distorted kagome metals LnTi3Bi4 as a promising platform for exploring novel emergent phases of matter at the intersection of strong correlation and magnetism. Published by the American Physical Society 2024

Janus monolayers Fe2SSeX2(X = Ga, In, and Tl): Robust nontrivial topology with high Chern-number

Abstract High-performance quantum anomalous Hall (QAH) systems are the crucial materials to explore emerging quantum physics and magnetic topological phenomena. Inspired by layered FeSe materials with excellent superconducting properties, the Janus monolayers Fe2SSeX2 (X = Ga, In, and Tl) are built by the decoration of Ga, In, and Tl atoms in monolayer Fe2SSe. Using the first-principles calculations, the Fe2SSeX2 have stable structures and prefer ferromagnetic (FM) orders, which belong to the Weyl semimetal without spin-orbit coupling (SOC). For the out-of-plane (OOP) magnetic anisotropy, the large nontrivial gaps are opened, and the Fe2SSeX2 are predicted to be large-gap QAH insulators with high Chern-number C = 2, proved by two chiral edge states and Berry curvatures. When the magnetization is flipped, two chiral edge states can be simultaneously changed and C = -2 can be obtained, revealing one fascinating behavior of chiral spin-edge-state locking. It is found that the QAH properties of the Fe2SSeX2 are robust against the strain. Especially, the nontrivial topological quantum states can spontaneously appear for the Fe2SSeGa2 and Fe2SSeIn2, because the easy magnetic axis orientations are adjusted from in-plane to OOP by the biaxial strain. Our studies provide excellent candidate systems to realize the QAH properties with high Chern-number, and advocate more experimental explorations in the combination of superconductivity and topology.

High switching ratio of antiferromagnetic order in thick sputtered Mn3+xSn1−x films by spin–orbit torque

Electrical manipulation of the antiferromagnetic states of Weyl semimetal Mn3Sn by current-induced spin–orbit torque (SOT) has attracted intensive attention recently, largely due to its potential advantage for high-density integration and ultrafast operation. In this study, the relation between the antiferromagnetic SOT switching ratio and the composition of Mn3+xSn1−x films was explored systematically. While SOT manipulation of ferromagnetic order has traditionally been confined to films just a few nanometers in thickness, our results indicate that current-induced SOT can effectively switch the antiferromagnetic order of sputtered Mn3+xSn1−x films with a thickness of up to 100 nm. Notably, a high electrical switching ratio of 83% was obtained in the optimized film with a composition of Mn3.1Sn0.9. The switching of the octupole polarization in thick Mn3Sn films may be accounted for by a seeded SOT mechanism. Joule heating of the Mn3Sn film close to the Néel temperature plays a key role in this switching process. Additionally, the factors influencing the switching ratio were further investigated. This work will deepen our understanding of the electrical switching mechanism of non-collinear antiferromagnetic order in Mn3Sn film and promote the development of antiferromagnetic spintronic devices.

Ground state magnetic structure and magnetic field effects in the layered honeycomb antiferromagnet YbOCl

YbOCl is a representative member of the van der Waals layered honeycomb rare-earth chalcohalide RChX (R = rare earth; Ch = O, S, Se, and Te; and X = F, Cl, Br, and I) family reported recently. Its spin ground state remains to be explored experimentally. We grew high-quality single crystals of YbOCl and conducted comprehensive thermodynamic, elastic, and inelastic neutron scattering experiments down to 50 mK. The experiments reveal an antiferromagnetic phase below 1.3 K which is identified as a spin ground state with an intralayer ferromagnetic and interlayer antiferromagnetic ordering. By applying sophisticated numerical techniques to a honeycomb (nearest-neighbor)–triangle (next-nearest-neighbor) model Hamiltonian which accurately describes the highly anisotropic spin system, we are able to simulate the experiments well and determine the diagonal and off-diagonal spin-exchange interactions. The simulations give an antiferromagnetic Kitaev term comparable to the Heisenberg one. The experiments under magnetic fields allow us to establish a magnetic field–temperature phase diagram around the spin ground state. Most interestingly, a relatively small magnetic field (∼0.3 to 3 T) can significantly suppress the antiferromagnetic order, suggesting an intriguing interplay of the Kitaev interaction and magnetic fields in the spin system. The present study provides fundamental insights into the highly anisotropic spin systems and opens a window to look into Kitaev spin physics in a rare-earth-based system. Published by the American Physical Society 2024