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Confinement-Induced Giant Spin-Orbit-Coupled Magnetic Moment of Co Nanoclusters in TiO2 Films
摘要： High magnetization materials are in great demand for the fabrication of advanced multifunctional magnetic devices. Notwithstanding this demand, the development of new materials with these attributes has been relatively slow. In this work, we propose a new strategy to achieve high magnetic moments above room temperature. Our materials engineering approach invoked the embedding of magnetic nanoclusters in an oxide matrix. By precisely controlling pulsed laser deposition parameters, Co nanoclusters are formed in a 5 at.% Co-TiO2 film. The presence of these nanoclusters was confirmed using transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray absorption fine structure. The film exhibits a very high saturation magnetization of 99 emu/cm3. Detailed studies using X-ray magnetic circular dichroism confirm that Co has an enhanced magnetic moment of 3.5 μB/atom, whilst the Ti and O also contribute to the magnetic moments. First principles calculations supported our hypothesis that the metallic Co nanoclusters surrounded by a TiO2 matrix can exhibit both large spin and orbital moments. Moreover, a quantum confinement effect results in a high Curie temperature for the embedded Co nanoclusters. These findings reveal that 1-2 nm nanoclusters that are quantum confined can exhibit very large magnetic moments above room temperature, representing a promising advance for the design of new high magnetization materials.
关键词： TiO2,Quantum,Ferromagnetism,Enhanced magnetic moment,Confinement effect,Nanoclusters
更新于2025-09-11 14:15:04
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Spin-polarized optical properties of half-metallic binary XBi (X?=?Ca, Sr and Ba) compounds in zinc blende and wurtzite phases
摘要： In this work, we aim to study the spin-polarized optical properties of the non-transition metal-based binary compounds XBi (X = Ba, Sr and Ca) in the zinc blende and wurtzite phases. The calculations are performed by the developed full-potential augmented plane wave plus local orbitals (FP-L/APW ? lo) method within the spin density functional theory. We used the Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (PBE-GGA) and the recently modi?ed Becke–Johnson potential (mBJ-GGA) to generate the exchange–correlation potential. The optical constants as the dielectric function, refractive index and extinction coef?cient were calculated and discussed in detail. Our compounds are identi?ed as potential candidates for spintronic applications and high-performance electronic devices, due to their possible half-metallic character. The interband transitions responsible for the structures in the spectra are speci?ed. It is shown that the Bi-p states and (Ca, Sr, Ba)-d states play the major role in optical transitions as initial and ?nal states.
关键词： Ferromagnetism,DFT,Half-metal,Optical properties
更新于2025-09-10 09:29:36
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First-principles investigation on the interlayer doping of SnSe2 bilayer
摘要： Using density functional theory calculations, we systematically investigated the effects of numbers and types of transition metals (TM) on the magnetic property of SnSe2 bilayer nanosheet. Our results revealed that, when one TM is introduced into the interlayer, the magnetic moment induced by the Co and Ni is tiny while it is largely strengthened with the doping of V, Cr, Mn, and Fe. When two TMs are inserted into the interlayer, Vand Cr make the system change into a weak antiferromagnetism (AFM) state while Mn-, Fe-, Co-doped systems display a weak ferromagnetism (FM) ground state. These FM states have the magnetic moments which double those of the one TM–doping systems. With the TM numbers further increasing to four, the robust AFM and FM features appear with the doping of Fe and Mn, respectively. Ni cannot induce any magnetism whatever the numbers of Ni are filling in. Interestingly, with the increase of the numbers of dopants, transitions from FM to AFM and AFM to FM are predicted to be realized on Fe-SnSe2 and Cr-SnSe2 systems, respectively. This kind of transition may be important for the applications in spintronic devices.
关键词： Interlayer doping,Spintronics application,Density functional theory,Antiferromagnetism,Modeling and simulation,Ferromagnetism,SnSe2
更新于2025-09-10 09:29:36
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Reference Module in Materials Science and Materials Engineering || III-V and Group-IV-Based Ferromagnetic Semiconductors for Spintronics
摘要： From the first development of the transistor, the rapid growth of solid-state electronic circuits has been quite impressive. Innovations of semiconductor (SC) processing technologies have helped keep the pace of developing smaller electronic devices with higher performance. Operations of most electronic devices rely on the ability to control the flow of charges. However, when electronic devices reach the scale of 10 nm or even smaller, two big problems appear. First, many kinds of fluctuation make it difficult to control the flow of electron charges. For example, when the channel length of field effect transistors (FETs) reaches several nanometers, the transport of electrons cannot be described by the conventional diffusion equation. In nanoscale devices, even fluctuation of positions of doped atoms strongly affects the movement of electrons, making it difficult to predict and control the output current. This results in large fluctuation of device parameters. The second problem is the leak off-current that results in the large idling energy dissipation. When the channel length reaches sub-10 nm, the leak off-current appears due to the quantum tunneling effect. As the device size becomes smaller, a larger number of devices working at higher speed are integrated. Thus, larger idling energy is consumed. To overcome these problems, many emerging technologies are being explored and developed. One of the prospective technologies, called 'spintronics,' may help us to find solutions or a totally new framework of electronics.
关键词： Group-IV semiconductors,ferromagnetic semiconductors,Mn-doped,Fe-doped,electrical control of ferromagnetism,III-V semiconductors,tunneling magnetoresistance,spintronics
更新于2025-09-10 09:29:36
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Synthesis and characterization of Ni incorporated titanium dioxide thin films
摘要： Thin ?lms of insulating Ti1(cid:1)xNixO2 (x 5 0.00, 0.05, 0.10, and 0.15) are synthesized by the spray pyrolysis technique. All the ?lms are seen to crystallize into polycrystalline anatase phase of TiO2. However, weak signature of the NiTiO3 phase is also observed for the ?lms having higher Ni ion concentration. Optical absorption analysis suggests nonmonotonous band gap decrease from 3.67 to 3.59 eV with respect to added concentration of Ni ions unto ‘x’ 5 0.10 in the TiO2 matrix. The presence of ferromagnetic ordering at room temperature in Ni incorporated TiO2 ?lms is revealed by M–H measurements. Calculated values of saturation magnetization indicate that the observed ferromagnetism is not due to the presence of Ni clusters or segregation of other ferromagnetic phase. Electrically insulating nature of the ?lms suggests that the observed FM ordering is most probably due to the ferromagnetic interaction between bound magnetic polarons which formed due to the creation of oxygen vacancies or defects.
关键词： ferromagnetism,Ni incorporated titanium dioxide,spray pyrolysis,optical properties,thin films
更新于2025-09-10 09:29:36
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Half-Metallic Ferromagnetism Character in Cr-Doped CaS Diluted Magnetic Insulator and Semiconductor: an Ab Initio Study
摘要： The overall aim of this study is to investigate theoretically the structural, electronic, and magnetic properties of calcium sulfide (CaS) doped with chromium (Cr) impurity, in order to conduct a new search dilute magnetic semiconductors (DMS) suitable for different applications in electronics and spintronics. For measuring, the physical property of this compound is implemented using the first principles approach employed in WIEN2K code. The structural characteristics are optimized using the Generalized Gradient Approximation established by Perdew-Burk-Ernzerhof (PBE-GGA). We calculate and minimize the total energy of the three ternary compounds (Ca0.75Cr0.25S, Ca0.50Cr0.50S, and Ca0.25Cr0.75S) in the paramagnetic (PM), ferromagnetic (FM), and antiferromagnetic (AFM) phase. We find all compounds stable in (FM) structure, whereas the modified Becke and Johnson local density approximation (mBJ-LDA) functional has been employed to evaluate the electronic and magnetic properties. Based on our findings, indicate that this system revealed a half-metallic ferromagnetic behavior with half-metallic gap (HM) and 100% spin-polarized at the fermi level for all chromium (Cr) concentrations. This advantageous set of properties is due to the half-metallic behavior, where the majority spin and minority spin exhibit metallic and semiconducting behaviors respectively. The chromium atom is the most important source of the total magnetic moment in these compounds (4 μβ) by comparison with magnetic moments produced by Ca and S atoms, which have minor contribution. Finally, our prediction results require an experimental confirmation in the future.
关键词： Diluted magnetic insulators (DMI),Spintronics,CaS,HM ferromagnetism,Density functional theory (DFT)
更新于2025-09-10 09:29:36
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Two-dimensional Dy doped MoS2 ferromagnetic sheets
摘要： Magnetic two-dimensional materials have attracted immense consideration as spintronic devices. However, design and synthesis of the magnetic two-dimensional MoS2 crystals with more controllable electronic structure and better conductivity are still great challenges. Here, we make a breakthrough to synthesize the MoS2:Dy sheets with robust adjustable room-temperature ferromagnetic properties by a gas-liquid chemical deposition method. The as-synthesized samples are characterized by XRD, Raman, TEM, HRTEM and XPS. Furthermore, the magnetic properties of the samples are also investigated by VSM and Squid. The maximum observed saturation magnetization is 0.023 emu/g. The origin of ferromagnetism in the samples is investigated by using the ?rst-principles calculations based on the density functional theory. The ferromagnetism is mainly related to the exchange interactions among the S 3p, Mo 4d and Dy 5d orbits. The results indicate that the transformation of the localized charges can e?ectively engineer and manipulate the magnetic properties of 2D materials, making MoS2 a potential candidate for spintronics and electronic applications and providing a new perspective on other 2D layered materials in spintronics application.
关键词： High pressure,2D materials,MoS2,First principles calculations,Ferromagnetism,Dy doping
更新于2025-09-10 09:29:36
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The electronic structure and magnetic property of the Mn doped β-Ga2O3
摘要： Ga2O3 is a promising candidate for high power, high voltage devices. In this work, the band structure of the pure β-Ga2O3 and the impact of orbital coupling on the Mn doped β-Ga2O3 electronic structure are analyzed based on density functional theory. The Mn dopant induces impurity bands near the band edge, resulting in the decrease of the band gap of the Ga2O3. When the Mn dopants only substitute the octahedrally coordinated Ga atoms, the doped systems possess the most stable structure and the ferromagnetism, the Monte Carlo simulation predicts that the Curie temperature is 421K. The room temperature ferromagnetism can be ascribed to the strong p-d coupling and the delocalization of O-2p orbital. The oxygen vacancy and gallium vacancy can induce the deep donor level and acceptor level into the band gap, respectively. Due to the valence change of Mn dopant, the Mn dopant undergoes a transition from donor to acceptor when the substrate obtains more carriers. Our results not only explain the observed electronic and magnetic properties in experiment, but also provide a theoretical model for designing high performance Ga2O3 based devices.
关键词： β-Ga2O3,Density Functional Theory,Electronic Structure,Ferromagnetism
更新于2025-09-10 09:29:36
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Rare Earth and Transition Metal Doping of Semiconductor Materials || Gadolinium-doped gallium-nitride
摘要： The race toward a dilute magnetic semiconductor (DMS) that exhibits room-temperature (RT) ferromagnetism has been in progress for about 15 years, sparked by the theoretical prediction that the two wide band-gap semiconductors GaN and ZnO would show a Curie temperature (TC) above 300 K if doped with 5% of Mn and a large hole concentration of 1 (cid:1) 1020/cm3 (Dietl et al., 2000). Despite apparent experimental evidence that RT magnetic order was already reported by many groups shortly after the theoretical prediction, the subject remained unusually controversial in the following years. Dietl (2010) summarizes that after 10 years of research the existence of ferromagnetism is well established for GaAs:Mn and related systems but it remains the major goal in the ?eld to achieve TCs at or above 300 K. Around the same time a review of a large group of theorists summarize: “The results of ab initio calculations seem to suggest that it is rather unlikely to obtain TC values as high as room temperature or above in this range” (Sato et al., 2010). Nonetheless persistent experimental claims of TCs above 300 K for a range of DMS materials can be found up to today. Thus it is worth trying to get a broader view on a given materials systems and compare a range of samples from different sources to elucidate whether these reports are characteristic of the DMS material itself (system-speci?c) or if only peculiarities of a given specimen are reported (sample-speci?c). Only in the former case can we consider those ?ndings to be useful for future potential applications in spintronic devices that have to be operational at ambient conditions.
关键词： ferromagnetism,room-temperature,GaN,Gd doping,dilute magnetic semiconductor
更新于2025-09-09 09:28:46
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Influence of the Quantum Well Structure and Growth Temperature on a Five-Layer InGaMnAs Quantum Well with an InGaAs Buffer Layer
摘要： The in?uence of quantum well structure and growth temperature on a synthesized multilayer system composed of a ?ve-layer InMnGaAs quantum well with an InGaAs buffer layer grown on semi-insulating (100)-oriented substrates prepared by low temperature molecular beam epitaxy was studied. The magnetization measurements using a superconducting quantum interference device indicated the existence of ferromagnetism with a Curie temperature above room temperature in the ?ve-layer InGaMnAs quantum well structure with an InGaAs buffer layer in a GaAs matrix. X-ray diffraction and secondary ion mass spectroscopy measurements con?rmed the second phase formation of ferromagnetic GaMn clusters. The ferromagnetism that exists in the ?ve-layer of the InMnGaAs quantum well with the InGaAs buffer layer results from a superposition of the ferromagnetism of the low temperature region from the substitutional Mn ions into Ga sites or interstitial Mn ions as well as the presence of manganese ions dopant clusters such as GaMn clusters.
关键词： Molecular Beam Epitaxy,Clusters,Ferromagnetism,Quantum Wells
更新于2025-09-09 09:28:46