Magnetic Heterojunction Research Articles

Easily reusable g-C3N4/NiFe2O4 magnetic heterojunction material for tetracycline degradation by visible light

To efficiently degrade tetracycline (TC) in water, magnetic reusable g-C3N4/NiFe2O4 heterojunction photocatalyst was synthesized by thermal polymerization and hydrothermal method. The obtained heterojunction photocatalyst achieved efficient degradation by degrading 86 % of TC in 2 h under visible light irradiation. and showed excellent magnetic reusable performance. The heterostructure formed between g-C3N4 and NiFe2O4 improved the separation efficiency and photoresponse range of photogenerated electrons and holes, and thus improved the photocatalytic degradation performance of the material. This study provides a new strategy for the efficient degradation of TC in water under visible light.

The shot noise in quasi-one-dimensional single spin filter magnetic heterojunctions

Based on the free electronic model and Büttike’s theory on shot noise, we investigated the shot noise of spin electrons in ferromagnetic/non-ferromagnetic insulator/spin filter layer/normal metal (FM/I/SF/NM) quasi-one-dimensional single spin filter tunneling junctions. The calculation results show that the barrier heights and thicknesses of the insulator and spin filter layers strongly affect the values and phases of the Fano factors of spin electrons. Compared with the traditional sandwich structures of ferromagnetic/spin filter layer/normal metal (FM/SF/NM) and ferromagnetic/non-ferromagnetic insulator/normal metal (FM/I/NM), when the thicknesses of the insulator and spin filter layers are very small, in single spin filter magnetic heterojunctions (FM/I/SF/NM), the insulator layer can suppress the Fano factors, while the spin filter layer is easier to separate the Fano factors of electrons whose spin directions are different. Further analysis shows that whether the Rashba coupling in the spin filter layer has an obvious influence on the Fano factors of spin electrons depends on the thickness of the spin filter layer. On the other hand, the Fano factors are strongly dependent on the sizes and directions of the molecular fields of the ferromagnet and spin filter layers. In addition, the electrons are incident with low energy or high energy, and the barrier heights and thicknesses of the spin filter layer and the thicknesses of the insulation layer have a significant effect on the spin-direction-dependent Fano factors of electrons.

Spin-Orbit Torque in Single-Molecule Junctions from ab Initio.

The use of electric fields applied across magnetic heterojunctions that lack spatial inversion symmetry has been previously proposed as a nonmagnetic means of controlling localized magnetic moments through spin-orbit torques (SOT). The implementation of this concept at the single-molecule level has remained a challenge, however. Here, we present first-principles calculations of SOT in a single-molecule junction under bias and beyond linear response. Employing a self-consistency scheme invoking density functional theory and nonequilibrium Green's function theory including spin-orbit interaction, we compute the change of the magnetization with the bias voltage and the associated current-induced SOT. Within the linear regime our quantitative estimates for the SOT in single-molecule junctions yield values similar to those known for magnetic interfaces. Our findings contribute to an improved microscopic understanding of SOT in single molecules.

Modulation of switching current density in T-type magnetic structure through magnetic anisotropy

We investigate magnetic field driven domain wall motion and spin-orbit torque (SOT) induced perpendicular magnetization switching of the ferrimagnetic layer in a T-type magnetic heterojunction with the structure of Pt/Co/Ta/Co81Tb19/Ta, where the bottom Co layer has in-plane magnetic anisotropy and the top Co81Tb19 layer has perpendicular magnetic anisotropy. It is found that the magnetic field driven domain wall motion and the depinning field of the Co81Tb19 layer can be effectively tuned by the thickness of the Co layer (tCo). Meanwhile, SOT-induced perpendicular magnetization switching of the Co81Tb19 layer is observed, and the critical switching current density first decreases and then increases with increasing the thickness of the Co layer. A lower critical switching current density was obtained at the optimized thickness (tCo = 1.2 nm), resulting in a 37% reduction in critical switching current density. Meanwhile, the research reveals a strong correlation between critical switching current density and magnetic anisotropy field, indicating that tuning the magnetic anisotropy is an efficient way to modulate the switching current density in a T-type magnetic structure. These results provide a new perspective on SOT manipulation and will be useful for the design of SOT-based devices.

Effect of Cu doping on the electronic structure, magnetic and optical properties of GaN/ZnS heterojunctions: a first-principles study

In this paper, the generalized gradient approximation method in density functional theory is adopted to calculate the GaN/ZnS heterojunction system with coexistence of Cu doping and point defects. The electronic structure, magnetic coupling mechanism and optical properties of each system are analyzed. It is shown by the research results that broader band gap width tuning (0.26–2.92 eV) can be achieved in the interface region of the Cu-doped GaN/ZnS heterojunction system. The magnetic sources of the system have two aspects, on the one hand, unpaired electrons are induced by cation vacancies to undergo spin polarization, thereby magnetic moments are contributed to the system, on the other hand, The GaN/ZnS heterojunction is induced by Cu doping to generate bound magnetic polarons, causing a magnetic phase transition in the system, and the total magnetic moment of the system is restricted by the concentration of bound magnetic polarons. In terms of optical properties, deep energy levels are introduced and hole-electron recombination centers are formed in the Cu-doped heterojunction system containing Ga vacancies. Compared with the non-magnetic heterojunction system, the magnetic heterojunction system exhibits a higher absorption intensity for visible light, and the redshift of its absorption spectrum is more pronounced. Furthermore, when the Cu-doped GaN/ZnS heterojunction system contains different vacancy defects, different conductive types can be achieved.

2D Heterostructure of CoCl2 /Co3 O4 Built for Strong Enhanced Magnetism.

As a remarkable structure, 2D magnetic heterojunctions have attracted researchers' attention owing to their controlled manipulation in the electronic device. However, successful fabrication as well as modulation of their structure and compound remain challenging. Herein, a novel method is designed to obtain a CoCl2 /Co3 O4 heterojunction on Si/SiO2 substrate with the assistance of supercritical CO2 (SC CO2 ), and the as-fabricated sample has significantly increased coercivity and saturation magnetization, which is 11 times higher than pure Co3 O4 . Further, it can be found that the CO2 pressure has the decisive effect on the saturation magnetization of the sample. Therefore, it suggests that the tunable electronic-magnetic device can be anticipated to be obtained in the future.

The Stack Optimization of Magnetic Heterojunction Structures for Next-Generation Spintronic Logic Applications.

Magnetic heterojunction structures with a suppressed interfacial Dzyaloshinskii-Moriya interaction and a sustainable long-range interlayer exchange coupling are achieved with an ultrathin platinum insertion layer. The systematic inelastic light scattering spectroscopy measurements indicate that the insertion layer restores the symmetry of the system and, then, the interfacial Dzyaloshinskii-Moriya interaction, which can prevent the identical magnetic domain wall motions, is obviously minimized. Nevertheless, the strong interlayer exchange coupling of the system is maintained. Consequently, synthetic ferromagnetic and antiferromagnetic exchange couplings as a function of the ruthenium layer thickness are observed as well. Therefore, these optimized magnetic multilayer stacks can avoid crucial issues, such as domain wall tilting and position problems, for next-generation spintronic logic applications. Moreover, the synthetic antiferromagnetic coupling can open a new path to develop a radically different NOT gate via current-induced magnetic domain wall motions and inversions.

Determining perpendicular magnetic anisotropy in Fe/MgO/Fe magnetic tunnel junction: A DFT-based spin–orbit torque method

In our JunPy package, we have combined the first-principles calculated self-consistent Hamiltonian with divide-and-conquer technique to successfully determine the magnetic anisotropy (MA) in an Fe/MgO/Fe magnetic tunnel junction (MTJ). We propose a comprehensive analytical derivation to clarify the crucial roles of spin–orbit coupling that mediates the exchange and spin–orbit components of spin torque, and the kinetic and spin–orbit components of spin current accumulation. The angular dependence of cumulative spin–orbit torque (SOT) indicates a uniaxial MA corresponding to the out-of-plane rotations of magnetic moments of the free Fe layers. Different from the conventional MA energy calculation and the phenomenological theory for a whole MTJ, our results provide insight into the orbital-resolved SOT for atomistic spin dynamics simulation in emergency complex magnetic heterojunctions.

Manipulating exchange bias in 2D magnetic heterojunction for high-performance robust memory applications

The exchange bias (EB) effect plays an undisputed role in the development of highly sensitive, robust, and high-density spintronic devices in magnetic data storage. However, the weak EB field, low blocking temperature, as well as the lack of modulation methods, seriously limit the application of EB in van der Waals (vdW) spintronic devices. Here, we utilized pressure engineering to tune the vdW spacing of the two-dimensional (2D) FePSe3/Fe3GeTe2 heterostructures. The EB field (HEB, from 29.2 mT to 111.2 mT) and blocking temperature (Tb, from 20 K to 110 K) are significantly enhanced, and a highly sensitive and robust spin valve is demonstrated. Interestingly, this enhancement of the EB effect was extended to exposed Fe3GeTe2, due to the single-domain nature of Fe3GeTe2. Our findings provide opportunities for the producing, exploring, and tuning of magnetic vdW heterostructures with strong interlayer coupling, thereby enabling customized 2D spintronic devices in the future.

Electric field tunable multi-state tunnel magnetoresistances in 2D van der Waals magnetic heterojunctions

Magnetic tunnel junction (MTJ) based on van der Waals (vdW) magnetic layers has been found to present excellent tunneling magnetoresistance (TMR) property, which has great potential applications in field sensing, nonvolatile magnetic random access memories, and spin logics. Although MTJs composed of multilayer vdW magnetic homojunction have been extensively investigated, the ones composed of vdW magnetic heterojunction are still to be explored. Here, we use first-principles approaches to reveal that the magnetic heterojunction MTJs have much more distinguishable TMR values than the homojunction ones. In the MTJ composed of bilayer CrI3/bilayer Cr2Ge2Te6 heterojunction, we find there are eight stable magnetic states, leading to six distinguishable electronic resistances. As a result, five sizable TMRs larger than 300% can be obtained (the maximum TMR is up to 620 000%). Six distinguishable memories are obtained, which is two times larger than that of a four-layered homojunction MTJ. The underlying relationships among magnetic state, spin-polarized band structures, and transmission spectra are further revealed to explain the multiple TMR values. We also find that the magnetic states, and thus TMRs, can be efficiently modulated by an external electric field. This study opens an avenue to the design of high-performance MTJ devices based on vdW heterojunctions.

Tetracycline removal by a magnetic heterojunction Cu2O/CoFe2O4 activating peroxymonosulfate

Tetracycline removal by a magnetic heterojunction Cu2O/CoFe2O4 activating peroxymonosulfate

Construction of magnetically recoverable MnZnFe2O4@Ag3PO4 Z-scheme photocatalyst for rapid visible-light-driven phenol degradation.

Visible-light-driven magnetic heterojunction as a promising photocatalysts has received much attention in environmental remediation. In this work, novel Z-scheme heterojunction MnZnFe2O4@Ag3PO4 (MZFO@APO) magnetic photocatalysts with excellent visible-light-driven photocatalytic activity are successfully constructed and characterized. The photocatalytic activity for phenol degradation is measured, and photodegradation mechanism is investigated with EPR, radical trapping experiments, and LC-MS. It turns out that the heterojunction introduced MZFO exhibits good adsorption effect on visible light and the direct Z-scheme bandgap alignment of MZFO and APO significantly improves charge separation and electron transfer, outperforming that of pure APO. MZFO@APO-40% with 40% APO content shows the rapid photodegradation performance, obtaining a 100% removal efficiency of phenol (25mg L-1) after 12-min visible light irradiation, and its kinetic constants are approximately 25.3 and 4.9 times higher than that of P25 TiO2 and pure APO, respectively. Especially, MZFO@APO-40% also possesses a high magnetic separation property and can be efficiently reused for 5 cycles. Additionally, EPR and radical trapping experiments confirm that h+, O2-, and 1O2 are the main active species in the photocatalytic process. Hydroquinone and small molecular organic acids such as maleic acid and oxalic acid are detected by LC-MS, which further indicates that the pathway of phenol degradation involves hydroxylation, open-ring reactions, and mineralization reactions. The novel addition of MZFO in photocatalyst construction has the potential to promote its application in environmental remediation.

Boosting visible light photocatalysis in BiOI/BaFe12O19 magnetic heterojunction.

Many previous studies have underestimated the role of magnetic components in improving photocatalytic performance. It is significance to explore the migration mechanism of photoinduced carriers in magnetic heterojunction. Here, a magnetic heterojunction, BiOI/BaFe12O19, was synthesized by a simple preparation method. The optimal synthesis conditions and photocatalytic reaction conditions were explored. The growth mechanism of bismuth iodide oxide (BiOI) was elaborated by introducing a micromagnetic field stemming from barium ferrite (BaFe12O19). The electrochemical impedance spectroscopy (EIS), Mott-Schottky curve (MS), transient fluorescence spectrometer (PL), and photocurrent response plot (i ~ t) tests indicated that the BiOI/BaFe12O19 possessed a higher transfer capacity of electrons, higher separation efficiency of photoinduced carriers, stronger photocurrent response, and higher carriers density, compared with pure BiOI. The ultraviolet-visible diffuse reflectance spectrophotometer (UV-vis DRS), electron paramagnetic resonance spectrometer (EPR), MS, and quenching experiments revealed band structure configuration and migration mechanism of photoinduced carriers. The enhancement mechanism of photocatalysis and photocatalytic reaction mechanism was clearly proclaimed in BiOI/BaFe12O19 catalytic system.

“Magnetic Ni–Zn ferrite anchored on g-C3N4 as nano-photocatalyst for efficient photo-degradation of doxycycline from water”

In the present work, mixed-spinel ferrite anchored onto graphitic carbon nitride (GCN) was synthesized for mineralization of antibiotic pollutant from waste water. A Z-scheme g-C3N4/Ni0.5Zn0.5Fe2O4 nano heterojunction was fabricated by three step procedure: pyrolysis, solution combustion and mechanical grinding followed by annealing. The prepared photocatlyst was tested for degradation of Doxycycline (DC) drug under the natural sun light. Results revealed that the prepared heterojunction has maximum degradation efficiency of 97.10% pollutant in 60 min experiment. The Z-scheme heterojunction between g-C3N4 and Ni–Zn ferrite improves the photoinduced charges separation and protection of redox capability and therby increases the photo degradation efficiency. The scavenging experiments suggested that O2−● and h+ as main active species responsible for degradation of the antibiotic. In addition, the dopant variation can drive the shists in band gap and energy band positiong too which makes then excellent candidates for synthesizing tunable heterostructures with organic semiconductors. The work focusses on designing and developing of saimpler but efficient magnetic heterojunctions with superior redox capability for solar powered waste water treatment.

Correction: Synthesis and testing of photocatalytic potential of MgFe2O4/ZnO/perlite magnetic heterojunction for degradation of synthetic dyes

Correction: Synthesis and testing of photocatalytic potential of MgFe2O4/ZnO/perlite magnetic heterojunction for degradation of synthetic dyes

Self‐Intercalated Magnetic Heterostructures in 2D Chromium Telluride

Emerging 2D magnetic heterojunctions attract substantial interest due to their potential applications in spintronics. Achieving magnetic phase engineering with structural integrity in 2D heterojunctions is of paramount importance for their magnetism manipulation. Herein, starting with chromium ditelluride (CrTe2) as the backbone framework, various lateral and vertical magnetic heterojunctions are obtained via self‐intercalated 2D chromium telluride (CrxTey). A Cr2Te3‐Cr5Te8 lateral heterojunction prototype is demonstrated for the manipulation of magnetic moments under different magnitudes of magnetic excitation, showing a sharply stepped hysteresis loop with a dual spin‐flip transition at high Curie temperatures up to 150 and 210 K by magneto‐optical Kerr measurement. High‐resolution scanning transmission electron microscopy and first‐principles calculations reveal a preferred random location of Cr intercalants at the phase boundary, allowing lowering energy associated with crystal field splitting. The overall structural rigidity of chromium‐telluride heterostructure with magnetic phase decoupled behaviors is promising for 2D spintronic devices.

Synthesis and testing of photocatalytic potential of MgFe2O4/ZnO/perlite magnetic heterojunction for degradation of synthetic dyes

Synthesis and testing of photocatalytic potential of MgFe2O4/ZnO/perlite magnetic heterojunction for degradation of synthetic dyes

Spin filtering effect in intrinsic 2D magnetic semiconductor Cr2Ge2Te6

All van der Waals Fe3GeTe2/Cr2Ge2Te6/graphite magnetic heterojunctions have been fabricated via mechanical exfoliation and stacking, and their magnetotransport properties are studied in detail. At low bias voltages, large negative junction magnetoresistances have been observed and are attributed to spin-conserving tunneling transport across an insulating Cr2Ge2Te6 layer. With increasing bias, a crossover to Fowler–Nordheim tunneling takes place. The negative sign of the tunneling magnetoresistance suggests that the bottom of a conduction band in Cr2Ge2Te6 belongs to minority spins, opposite to the findings of some first-principles calculations. This work shows that the vdW heterostructures based on 2D magnetic insulators are a valuable platform to gain further insight into spin polarized tunneling transport, which is the basis for pursuing high performance spintronic devices and a large variety of quantum phenomena.

Spin‐Transport through Van der Waals Heterojunctions Based on 2D‐Ferromagnet and Transition Metal Dichalcogenides: A Study from First‐Principles Calculations

AbstractRecently reported 2D ferromagnets show tremendous potential for their application in low‐dimensional spintronic devices. Semiconductor heterostructure consisting of 2D ferromagnet integrated with other suitable 2D semiconducting materials may pave the way for designing robust and sophisticated spin‐transport devices within a few nanometer scales. In this regard, a detailed understanding of the interface properties of 2D ferromagnetic materials and other 2D semiconductors is highly essential. Herein, the interface properties in the heterostructure made‐up of CrX3 (X = Cl, Br, and I) monolayer and transition‐metal dichalcogenides (TMDC; MoS2, MoSe2, and WS2) monolayer, using first‐principle calculations are systematically studied. This study predicts that a robust spin‐dependent barrier originated at the CrX3/TMDC interface. It can lead to a significantly large spin‐filtering at the interface while spin‐transport through this heterojunction, which will be highly beneficial for spintronic devices applications. Further, detailed spin‐dependent transport studies carried out through Co/CrI3/TMDC/CrI3/Co magnetic heterojunctions and substantial tunnel magnetoresistance up to 590%, estimated for these systems.

Room temperature manipulation of exchange bias in magnetic heterojunctions

Emerging hybrid in-plane and out-of-plane devices have exposed the urgent demand for simultaneously in-plane and out-of-plane exchange biased layers in a single functional device. In this work, we have performed detailed studies on the manipulation of dual exchange bias in the IrMn/Co/Pt/CoPt/IrMn heterojunction. The in-plane exchange bias between IrMn and Co layers can be reversibly controlled by simultaneous application of colinear in-plane magnetic field and current pulse along x-direction. And the out-of-plane exchange bias between CoPt and IrMn layers can be manipulated by the application of out-of-plane external magnetic field along z-direction or colinear in-plane magnetic field and current pulse along x-direction. Moreover, thanks to the interlayer exchange coupling between Co/Pt/CoPt, a purely electrical induced spin-orbit torque switching can be used to manipulate the out-of-plane exchange bias. Based on this purely electrical manipulation of out-of-plane exchange bias, multistate nonvolatile memory has been demonstrated. Our work has revealed the promising application prospects of flexible manipulation of exchange bias in future multifunctional and multidimensional spintronic devices.