Magnetic Interface Research Articles

Local symmetry-driven interfacial magnetization and electronic states in (ZnO)n/(w-FeO)n superlattices.

Superlattices constructed with the wide-band-gap semiconductor ZnO and magnetic oxide FeO, both in the wurtzite structure, have been investigated using spin-polarized first-principles calculations. The structural, electronic and magnetic properties of the (ZnO)n/(w-FeO)n superlattices were studied in great detail. Two different interfaces in the (ZnO)n/(w-FeO)n superlattices were identified and they showed very different magnetic and electronic properties. Local symmetry-driven interfacial magnetization and electronic states can arise from different Fe/Zn distributions at different interfaces or spin ordering of Fe in the superlattice. The local symmetry-driven interfacial magnetization and electronic states, originating either from different Fe/Zn distribution across interfaces I and II, or by spin ordering of Fe in the superlattice, can be identified. It was also found that, in the case of the ferromagnetic phase, the electrons are more delocalized for the majority spin but strongly localized for the minority spin, which resulted in interesting spin-dependent transport properties. Our results will pave the way for designing novel spin-dependent electronic devices through the construction of superlattices from semiconductors and multiferroics.

Enhancing Interfacial Ferromagnetism and Magnetic Anisotropy of CaRuO3/SrTiO3 Superlattices via Substrate Orientation.

Artificial oxide heterostructures have provided promising platforms for the exploration of emergent quantum phases with extraordinary properties. One of the most interesting phenomena is the interfacial magnetism formed between two non-magnetic compounds. Here, a robust ferromagnetic phase emerged at the (111)-oriented heterointerface between paramagnetic CaRuO3 and diamagnetic SrTiO3 is reported. The Curie temperature is as high as ≈155K and the saturation magnetization is as large as ≈1.3µB per formula unit for the (111)-CaRuO3/SrTiO3 superlattices, which are obviously superior to those of the (001)-oriented counterparts and are comparable to the typical itinerant ferromagnet SrRuO3. A strong in-plane magnetic anisotropy with six-fold symmetry is further revealed by the anisotropic magnetoresistance measurements, presenting a large in-plane anisotropic field of 3.0-3.6T. More importantly, the magnetic easy axis of the (111)-oriented superlattices can be effectively tuned from 〈 1〉 to 〈 〉 directions by increasing the layer thickness of SrTiO3. The findings demonstrate a feasible approach to enhance the interface coupling effect by varying the stacking orientation of oxide heterostructures. The tunable magnetic anisotropy also shows potential applications in low-power-consumption or exchange spring devices.

Probing van der Waals magnetic surface and interface via circularly polarized X-rays

Advances in research of magnetic two-dimensional van der Waals (2D vdW) materials have opened up new opportunities in miniaturization of spintronic devices at the atomically thin limit. One major research thrust, which is the subject of this review, is that the magnetism of 2D vdW materials and their derived hetero-interface may be significantly affected by the local atomic geometry and environment. As a result, there is a pressing need for powerful advanced technique to characterize magnetic vdW surface and interface. Circularly polarized X-rays from synchrotron radiation light sources are key to this endeavor, as they can probe the microscopic magnetism of a specific element, for their atomic sensitivity, element-specificity, core-level excitation as well as capability of separation for the spin and orbit moments. We review a series of representative experimental achievements, exploiting circularly polarized X-rays, in (1) 2D vdW magnet, (2) magnetic metal/vdW interface, (3) molecule/vdW interface as well as (4) vdW/2D interface. On the basis of the review, advantages of probing magnetic vdW surface and interface by circularly polarized X-rays are presented, and challenges and opportunities are also discussed.

Composition-controlled magnetic proximity effects in CoFe2O4-CoFe-reduced graphene oxide composites prepared by a simple single-step sonochemical reduction method

A simple single-step sonochemical reduction method is used to prepare CoFe2O4-CoFe-reduced graphene oxide (rGO) composites (with varied amounts of CoFe2O4 and CoFe) under atmospheric conditions. The method enables in-situ reduction of graphene oxide (GO) to rGO and control of rGO content while the CoFe2O4-CoFe-rGO composites form. X-ray and electron diffraction and high-resolution electron microscopy revealed the formation of CoFe2O4-CoFe-rGO composites. The formation of the composites was further confirmed by Raman scattering analysis. Without rGO, an enhanced exchange coupling between soft CoFe and hard CoFe2O4 magnetic phases is observed. With rGO, tunable interfacial magnetic proximity-induced magnetization at the interface of CoFe2O4-CoFe and rGO is observed.

Probing the strongly correlated magnetic state of Co2C nanoparticles at low temperatures using μSR

Co2C nanoparticles (NPs) are amongst transition metal carbides whose magnetic properties have not been well explored. An earlier study (Roy et al 2021 J. Phys.: Condens. Matter 33 375804) showed that a pellet made from Co2C NPs exhibits exchange bias (EB) effect below a temperature, T EB = 50 K and a spin glass (SG) feature emerges below T SG = 5 K. In the current study we use magnetic, electrical transport, specific heat, and muon spin rotation (μSR) measurements to explore further the magnetic properties of a pellet made with 40 nm diameter pure Co2C NPs. We uncover the onset of Kondo localization at Kondo temperature T K (= 40.1 K), which is close to the onset temperature (T EB) of the EB effect. A crossover from the Kondo-screened scenario to the Ruderman–Kittel–Kasuya–Yosida interaction-dominated regime is also observed for T < T K. Temperature-dependent specific heat measurement further supports the Kondo localization scenario in the pellet and shows the heavy fermionic nature of the strongly correlated electronic state in Co2C. The zero field μSR asymmetry spectra in the low-temperature regime are characterized by two distinct fast and slow relaxation rates. The spectra show the absence of long-range magnetic order in the sample. However, our analysis suggests the NPs-pellet shows the presence of a dominant magnetically disordered fraction and a smaller fraction with short-range order. Muons in the disordered fraction exhibit a slower relaxation rate, while muons in the smaller fraction with short-range order exhibit a faster relaxation rate. We observe an increase in this fast relaxation rate between T EB and T SG. This increase below T EB ∼ 50 K suggests a slowing down of the fluctuating local magnetic environment around muons. Transverse field-μSR asymmetry spectra show the emergence of a stable, multi-peaked local magnetic field distribution in the pellet below T EB. Longitudinal field μSR spectra shows distinct changes in the dynamics of fluctuations suggesting the presence of a frozen glassy like state below 6 K. Based on our results, we suggest that below T EB, the pellet of Co2C NPs develops a magnetic interface that separates the two magnetic fractions; one is a disordered fraction, and the other is a fraction with short-range order. The exchange interaction that sets in below T EB at the interface couples the two fractions, leading to a suppression of the fluctuations. With the suppression of magnetic fluctuations below T EB, strong correlation effects in the electronic state of Co2C lead to Kondo localization.

Bound band in the continuum from merging of topological edge states and magnetic interface states

The bandwidth of topological edge states (TESs) or other waveguides in photonic crystals (PCs) are always limited by the width of bandgap. In order to break this limitation, we propose a new concept of bound bands in the continuum. Through constructing a hexagonal lattice of gyromagnetic rods and optimizing the structure parameters, we find that the TESs and magnetic interface states (MISs) can be merged to form a unique bound band. The bound band can pass through the bulk bands from the bandgap and keep perfect localization field at the interface without hybridizing with bulk states even though they are degenerated at the same frequencies.

Emerging interfacial magnetization in isovalent manganite heterostructures driven by octahedral coupling

Emerging interfacial magnetization in isovalent manganite heterostructures driven by octahedral coupling

Paper-based lipid bilayer magnetic interface for ultrasensitive assay of tumor-derived extracellular vesicles PD-L1

Programmed death ligand 1 (PD-L1) of tumor-derived extracellular vesicles (T-EVs) is an important biomarker to predict immunotherapy response. The traditional bioassays of T-EVs PD-L1 are limited by the detection specificity because of the distribution of the signals by PD-L1 from nontumor-derived EVs, which leads to unsatisfactory predictive accuracy. In this work, we developed a simple and ultrasensitive method for the quantification of T-EVs PD-L1 by using the lipid bilayer magnetic interface as the isolation and enrichment carrier along with hybridization chain reaction (HCR) for signal amplification in a paper-based device. First, magnetic beads were covered by liposome bilayers and then anchored with the cholesterol modified epithelial cell adhesion molecule (EpCAM) aptamer to construct a fluid multivalent magnetic interface and realize the high-performance isolation of T-EVs. Moreover, the biosensor relied on the PD-L1 aptamer to initiate the HCR of EVs. Benefiting from the high isolation ability of the lipid bilayer magnetic interface and the high signal amplification ability of HCR, the dual-aptamer-based biosensor is capable of highly sensitive detection of T-EVs with a detection limit as low as 5.0 EVs·µL−1 in a paper-based device. Overall, the paper-based lipid bilayer magnetic interface biosensor not only can serve as an alternative tool for predicting the immunotherapy response but also displays great potential in point-of-care disease diagnosis.

Recent progress in the JARVIS infrastructure for next-generation data-driven materials design

The joint automated repository for various integrated simulations (JARVIS) infrastructure at the National Institute of Standards and Technology is a large-scale collection of curated datasets and tools with more than 80 000 materials and millions of properties. JARVIS uses a combination of electronic structure, artificial intelligence, advanced computation, and experimental methods to accelerate materials design. Here, we report some of the new features that were recently included in the infrastructure, such as (1) doubling the number of materials in the database since its first release, (2) including more accurate electronic structure methods such as quantum Monte Carlo, (3) including graph neural network-based materials design, (4) development of unified force-field, (5) development of a universal tight-binding model, (6) addition of computer-vision tools for advanced microscopy applications, (7) development of a natural language processing tool for text-generation and analysis, (8) debuting a large-scale benchmarking endeavor, (9) including quantum computing algorithms for solids, (10) integrating several experimental datasets, and (11) staging several community engagement and outreach events. New classes of materials, properties, and workflows added to the database include superconductors, two-dimensional (2D) magnets, magnetic topological materials, metal-organic frameworks, defects, and interface systems. The rich and reliable datasets, tools, documentation, and tutorials make JARVIS a unique platform for modern materials design. JARVIS ensures the openness of data and tools to enhance reproducibility and transparency and to promote a healthy and collaborative scientific environment.

Heterogeneous Interface Engineering of Bi‐Metal MOFs‐derived ZnFe2O4–ZnO‐Fe@C Microspheres via Confined Growth Strategy Toward Superior Electromagnetic Wave Absorption

AbstractHeterogeneous interface regulation plays an important role in tailoring the intrinsic electromagnetic (EM) properties for obtaining excellent EM wave absorption, which still faces huge challenge. In this work, bi‐metal MOFs‐derived ZnFe2O4–ZnO‐Fe@C (ZZFC) microspheres with custom‐built heterogeneous interfaces are successfully fabricated via a confined growth strategy. Bi‐metal Fe–Zn–ZIF with tailored coordination structure and chemical bonding are first selected as the precursor template. After undergoing the annealing process, the metal Fe2+ host is converted into magnetic Fe nanoparticles (NPs). The Zn2+ host is transformed into semiconductor zinc oxide (ZnO) with increasing (101) crystal‐oriented growth. At the same time, metal hosts Fe2+ and Zn2+ are further reacted to synthesize the zinc ferrite (ZnFe2O4). Formed Fe nanoparticles catalyze organic ligands to constitute graphitized carbon layers, which confine the further growth of ZnFe2O4, ZnO, and Fe NPs. Combined with the well impendence and synergy absorption mechanism (magnetic loss, interface polarization, and conduction loss), optimized magnetic–dielectric ZnFe2O4–ZnO‐Fe@C microspheres exhibit outstanding EM wave absorption with the minimum reflection loss −66.5 dB at only 2.0 mm thickness. Bi‐metal MOF‐derived magnetic–dielectric absorption materials with tailored heterogeneous interfaces provide a new sight to design an efficient EM wave absorption system.

A self-powered synchronous magnetic flux extraction interface for electromagnetic energy harvesting

In this work, a self-powered synchronous magnetic flux extraction (SP-SMFE) circuit is proposed for electromagnetic energy harvesting. It's a bridgeless direct ac-dc converter, that uses a large-value external inductor L to store and transfer energy. By comparing the voltage across L, SP-SMFE achieves the peak detection of the inductor current Iem without an external power supply and transfers the energy to the load when Iem reaches the peak value, which can maximize the energy extraction from the electromagnetic transducer. Simulation results show that the output power of SP-SMFE is much higher than that of the voltage doubler circuit under the load range of 1–100 kΩ and the frequency range of 20–140 Hz. The input ac voltage with 4 V amplitude is rectified and stepped up to 59 V dc by SP-SMFE at the load of 100 kΩ and the frequency of 40 Hz. Experiment results verify the effectiveness of the SP-SMFE circuit in power harvesting at low frequencies and large loads.

Magnetic Field-Assisted Interface Embedding Strategy to Construct 2D/3D Composite Structure for Stable Perovskite Solar Cells with Efficiency Over 24.

Perovskite solar cells (PSCs) based on 2D/3D composite structure have shown enormous potential to combine high efficiency of 3D perovskite with high stability of 2D perovskite. However, there are still substantial non-radiative losses produced from trap states at grain boundaries or on the surface of conventional 2D/3D composite structure perovskite film, which limits device performance and stability. In this work, a multifunctional magnetic field-assisted interfacial embedding strategy is developed to construct 2D/3D composite structure. The composite structure not only improves crystallinity and passivates defects of perovskite layer, but also can efficiently promote vertical hole transport and provide lateral barrier effect. Meanwhile, the composite structure also forms a good surface and internal encapsulation of 3D perovskite to inhibit water diffusion. As a result, the multifunctional effect effectively improves open-circuit voltage and fill factor, reaching maximum values of 1.246V and 81.36%, respectively, and finally achieves power conversion efficiency (PCE) of 24.21%. The unencapsulated devices also demonstrate highly improved long-term stability and humidity stability. Furthermore, an augmented performance of 21.23% is achieved, which is the highest PCE of flexible device based on 2D/3D composite perovskite films coupled with the best mechanical stability due to the 2D/3D alternating structure.

Research on dynamic coupling characteristics of magnetic fluid and gas medium interface in sealing devices

The widths and shapes of sealing interfaces are key indicators for characterizing the sealing stability of dynamic and static magnetic fluid seals. In this study, the interface of a magnetic fluid seal was numerically simulated and changes in the interfacial shape and width were tested and verified using a magnetic fluid seal device. The results showed that the pressure resistance decreased with an increase in seal clearance, and the magnetic fluid seal interface generated a small leakage channel. Following the complete formation of the leakage channel, the static seal gradually failed. During failure, the interface width of the magnetic fluid became narrow. At a certain pressure, the maximum pressure resistance decreased as a function of the rotational speed. Compared with a static seal, more small leakage channels and bubbles were generated. In constant conditions, such as fixed sealing clearance speed during dynamic and static sealing, the change in the width of the magnetic fluid interface of the dynamic seal was 5–7 times that of the static seal.

The Role of Magnetic Interfaces in the Formation of Forbidden Reflections

The Role of Magnetic Interfaces in the Formation of Forbidden Reflections

Optical forces in heat-assisted magnetic recording head-disk interface

A main challenge in Heat-Assisted Magnetic Recording technology is the build-up of contaminants called smear on the near field transducer. In this paper, we investigate the role of optical forces originating from the electric field gradient in the formation of smear. First, based on suitable theoretical approximations, we compare this force with air drag and the thermophoretic force in the head-disk interface for two smear nanoparticle shapes. Then, we evaluate the force field’s sensitivity to the relevant parameter space. We find that the smear nanoparticle’s refractive index, shape, and volume significantly impact the optical force. Further, our simulations reveal that the interface conditions, such as spacing and the presence of other contaminants, also influence the magnitude of the force.

Anisotropic spin-current spectroscopy of ferromagnetic superconducting gap symmetries

We develop a microscopic theory of tunneling spin transport at the magnetic interface between a ferromagnetic insulator (FI) and a ferromagnetic superconductor (FSC) driven by ferromagnetic resonance. We show that the spin susceptibilities of the FSC can be extracted from the spin currents by tuning the easy axis of the FI, and thus the spin currents can be a probe for the symmetries of the spin-triplet Cooper pairing. Our results will offer a route to exploiting the synergy of magnetism and superconductivities for spin devices.

Interfacial and surface magnetism in epitaxial NiCo2O4(001)/MgAl2O4 films

NiCo2O4 (NCO) films grown on MgAl2O4 (001) substrates have been studied using magnetometry and x-ray magnetic circular dichroism based on x-ray absorption spectroscopy and spin-polarized inverse photoemission spectroscopy with various thicknesses down to 1.6 nm. The magnetic behavior can be understood in terms of a layer of optimal NCO and an interfacial layer (1.2 ± 0.1 nm), with a small canting of magnetization at the surface. The thickness dependence of the optimal layer can be described by the finite-scaling theory with a critical exponent consistent with the high perpendicular magnetic anisotropy. The interfacial layer couples antiferromagnetically to the optimal layer, generating exchange-spring styled magnetic hysteresis in the thinnest films. The non-optimal and measurement-speed-dependent magnetic properties of the interfacial layer suggest substantial interfacial diffusion.

A Fluid Multivalent Magnetic Interface for High-Performance Isolation and Proteomic Profiling of Tumor-Derived Extracellular Vesicles.

Isolation and analysis of tumor-derived extracellular vesicles (T-EVs) are important for clinical cancer management. Here, we develop a fluid multivalent magnetic interface (FluidmagFace) in a microfluidic chip for high-performance isolation, release, and protein profiling of T-EVs. The FluidmagFace increases affinity by 105-fold with fluidity-enhanced multivalent binding to improve isolation efficiency by 13.9% compared with a non-fluid interface. Its anti-adsorption property and microfluidic hydrodynamic shear minimize contamination, increasing detection sensitivity by two orders of magnitude. Moreover, its reversibility and expandability allow high-throughput recovery of T-EVs for mass spectrometric protein analysis. With the chip, T-EVs are detected in all tested cancer samples with identification of differentially expressed proteins compared with healthy controls. The FluidmagFace opens a new avenue to isolation and release of targets for cancer diagnosis and biomarker discovery.

A Fluid Multivalent Magnetic Interface for High‐Performance Isolation and Proteomic Profiling of Tumor‐Derived Extracellular Vesicles

AbstractIsolation and analysis of tumor‐derived extracellular vesicles (T‐EVs) are important for clinical cancer management. Here, we develop a fluid multivalent magnetic interface (FluidmagFace) in a microfluidic chip for high‐performance isolation, release, and protein profiling of T‐EVs. The FluidmagFace increases affinity by 105‐fold with fluidity‐enhanced multivalent binding to improve isolation efficiency by 13.9 % compared with a non‐fluid interface. Its anti‐adsorption property and microfluidic hydrodynamic shear minimize contamination, increasing detection sensitivity by two orders of magnitude. Moreover, its reversibility and expandability allow high‐throughput recovery of T‐EVs for mass spectrometric protein analysis. With the chip, T‐EVs were detected in all tested cancer samples with identification of differentially expressed proteins compared with healthy controls. The FluidmagFace opens a new avenue to isolation and release of targets for cancer diagnosis and biomarker discovery.

Solid-State Lithium Ion Supercapacitor for Voltage Control of Skyrmions.

Ionic control of magnetism gives rise to high magnetoelectric coupling efficiencies at low voltages, which is essential for low-power magnetism-based nonconventional computing technologies. However, for on-chip applications, magnetoionic devices typically suffer from slow kinetics, poor cyclability, impractical liquid architectures, or strong ambient effects. As a route to overcoming these problems, we demonstrate a LiPON-based solid-state ionic supercapacitor with a magnetic Pt/Co40Fe40B20/Pt thin-film electrode which enables voltage control of a magnetic skyrmion state. Skyrmion nucleation and annihilation are caused by Li ion accumulation and depletion at the magnetic interface under an applied voltage. The skyrmion density can be controlled through dc applied voltages or through voltage pulses. The skyrmions are nucleated by single 60 μs voltage pulses, and devices are cycled 750000 times without loss of electrical performance. Our results demonstrate a simple and robust approach to ionic control of magnetism in spin-based devices.