Ferromagnetic Semiconductor Research Articles

P-Orbital Ferromagnetism Arising from Unconventional O- Ionic State in a New Semiconductor Sr2AlO4 with Insufficiently Bonded Oxygen.

Oxygen in solids usually exists in an O2- ionic state. As a result, it loses its magnetic nature of a single atom, wherein two unpaired electrons exist in its outer 2p orbitals. Here, it is shown that an unconventional stable ionic state of O- is realized in a new semiconductor material Sr2AlO4, leading to an intrinsic p-orbital ferromagnetism stable until ≈900K. Experimental and theoretical investigations have clarified that one-fourth of the oxygen atoms in Sr2AlO4 are insufficiently bonded in the crystal structure, resulting in a unique O--state and p-orbital ferromagnetism. To date, the O- state is reported to exist only in non-equilibrium conditions, and p-orbital magnetism is only suggested in impurity bands with small ferromagnetic moments. The present work provides a new route for creating ferromagnetism in semiconductors and exploring new p-orbital physics and chemistry. In addition, the material shows elastic-mechanoluminescence that may enable unprecedented mechano-photonic-spintronics.

Study of lanthanide based Ln2MgSe4 (Ln = Er, Pm) spinels for spintronic and optoelectronic applications

Abstract Herein, the full potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT) is used to examine the physical features of Ln2MgSe4 (Ln = Er, Pm) spinel selenides. Exchange correlation energies are estimated through modified Becke–Johnson potential (mBJ). Band structures (BS) and density of states (DOS) data proved that Er2MgSe4 is ferromagnetic (FM) semiconductor while Pm2MgSe4 is half metallic (HFM) ferromagnetic in nature. The Er-f contributed majorly to the vicinity of Fermi level for both compounds. The structural stability is determined through calculating the tolerance factor and geometry optimization, while thermodynamical stability has been realized by computing the formation enthalpy. Furthermore, various optical parameters have been computed which describe the considered materials’ response to incident light. Our study explored the physical properties of two Ln based spinels which are found to have potential for being used in various optoelectronic and spintronic devices.

Bragg resonances in left-handed bigyrotropic media based on periodic ferromagnetic semiconductor

In this work, a theoretical model for a periodic bigyrotropic left-handed medium, which is a ferromagnetic semiconductor, is developed. The presence of periodicity in such a structure leads to the formation of Bragg band gaps in the spectrum of propagating waves, both in the microwave and terahertz ranges. Band gaps in the microwave range are formed in the frequency region with double negative effective parameters of the medium. The band gaps density decreases with increasing frequency in the microwave range and increases in the terahertz range.

Importance of magnetic shape anisotropy in determining triaxial magnetic anisotropy of ferromagnetic semiconductor CrSCl monolayer

Abstract Magnetic anisotropy (MA) is pivotal for stabilizing long-range magnetic order in two-dimensional (2D) systems against thermal fluctuations. Here, we conduct a comprehensive investigation of the electronic and magnetic properties of CrSCl monolayer using first-principles methods and Monte Carlo (MC) simulations. Our results reveal that CrSCl monolayer exhibit a direct band gap ferromagnetic semiconductor (FMS) with a high Curie temperature (TC, 143 K). Notably, we identify triaxial magnetic anisotropy in this monolayer, characterized by the easy magnetization axis along the y-axis, intermediate axis along the x-axis, and hard axis along the z-axis. This anisotropy arises from a combination of magnetocrystalline anisotropy and shape anisotropy, in which shape anisotropy dominating over weak magnetocrystalline anisotropy. Orbital projection analysis shows that the major contribution of magnetic anisotropy energy comes from the d orbital of Cr atom. These findings provide some insights into the strain response of MA and suggest that studies of other FM monolayers may uncover future contenders for strain-switchable and ultra-compact spintronics devices.

Multiferroic properties and the layer-stacking quantum anomalous Hall effect in two-dimensional RuOHX (X = F, Cl, Br)

Exploring the physics coupled with layer degrees of freedom in materials has become a hot topic in quantum layertronics. We propose a robust second-order topological insulator monolayer RuOHX (X = F, Cl, and Br), a two-dimensional ferromagnetic semiconductor with large valley polarization, capable of undergoing topological phase transition induced by strain effect. In the bilayer RuOHX, we achieve layer-polarized anomalous Hall effect through interlayer sliding, originating from layer-stacking Berry curvature. Moreover, it can be controlled and reversed by the direction of ferroelectric polarization. Under appropriate biaxial strain, the bilayer RuOHX exhibits quantum layer spin Hall effect in which the helical edge states are manifested as spin-chirality-locking, due to the degeneracy of layer-polarized quantum anomalous Hall effect. Our work explores the potential application via layer-stacking topological properties for future quantum device applications.

Two-field measurements of spin-orbit-torque efficiency in crystalline (Ga,Mn)(As,P) ferromagnetic semiconductors

Two-field measurements of spin-orbit-torque efficiency in crystalline (Ga,Mn)(As,P) ferromagnetic semiconductors

Emerging two-dimensional ferromagnetic semiconductors.

Two-dimensional (2D) semiconductors have attracted considerable attention for their potential in extending Moore's law and advancing next-generation electronic devices. Notably, the discovery and development of 2D ferromagnetic semiconductors (FMSs) open exciting opportunities in manipulating both charge and spin, enabling the exploration of exotic properties and the design of innovative spintronic devices. In this review, we aim to offer a comprehensive summary of emerging 2D FMSs, covering their atomic structures, physical properties, preparation methods, growth mechanisms, magnetism modulation techniques, and potential applications. We begin with a brief introduction of the atomic structures and magnetic properties of novel 2D FMSs. Next, we delve into the latest advancements in the exotic physical properties of 2D FMSs. Following that, we summarize the growth methods, associated growth mechanisms, magnetism modulation techniques and spintronic applications of 2D FMSs. Finally, we offer insights into the challenges and potential applications of 2D FMSs, which may inspire further research in developing high-density, non-volatile storage devices based on 2D FMSs.

Experimental magnetic-semiconductor features of the theoretically half-metallic perovskite CaLaTiFeO6

Abstract In this manuscript, the synthesis process of the CaLaTiFeO6 material is shown. The crystallographic structure analysis reveals its monoclinic perovskite type nature (space group P21/n, #14), its morphological strongly granular characteristics, its optical response yields its semiconducting character with a 0.61 eV bandgap and its ferromagnetic property at temperatures T>350 K are reported. Likewise, calculations and analysis of the electronic properties are performed through Density Functional Theory, which showed correlation with the experimental results. The results allow classifying the CaLaTiFeO6 material as a ferromagnetic semiconductor at room temperature, making it a good candidate for the design of spintronic devices.

High temperature ferrimagnetic semiconductors by spin-dependent doping in high temperature antiferromagnets

To realize room temperature ferromagnetic (FM) semiconductors is still a challenge in spintronics. Many antiferromagnetic (AFM) insulators and semiconductors with high Neel temperature TN are obtained in experiments, such as LaFeO3, BiFeO3, etc. High concentrations of magnetic impurities can be doped into these AFM materials, but AFM state with very tiny net magnetic moments was obtained in experiments because the magnetic impurities were equally doped into the spin up and down sublattices of the AFM materials. Here, we propose that the effective magnetic field provided by a FM substrate could guarantee the spin-dependent doping in AFM materials, where the doped magnetic impurities prefer one sublattice of spins, and the ferrimagnetic (FIM) materials are obtained. To demonstrate this proposal, we study the Mn-doped AFM insulator LaFeO3 with FM substrate of Fe metal by the density functional theory (DFT) calculations. It is shown that the doped magnetic Mn impurities prefer to occupy one sublattice of the AFM insulator and introduce large magnetic moments in La(Fe, Mn)O3. For the AFM insulator LaFeO3 with high TN = 740 K, several FIM semiconductors with high Curie temperature TC > 300 K and the band gap less than 2 eV are obtained by DFT calculations when 1/8 or 1/4 Fe atoms in LaFeO3 are replaced by the other 3d, 4d transition metal elements. The large magneto-optical Kerr effect (MOKE) is obtained in these LaFeO3-based FIM semiconductors. In addition, the FIM semiconductors with high TC are also obtained by spin-dependent doping in some other AFM materials with high TN, including BiFeO3, SrTcO3, CaTcO3, etc. Our theoretical results propose a way to obtain high TC FIM semiconductors by spin-dependent doping in high TN AFM insulators and semiconductors.

Emergence of defects-mediated diluted ferromagnetic semiconductor (ZnS: La3+) Quantum Dots: A versatile platform for optoelectronic and spintronic applications

For the first time, La3+ ions incorporated into semiconductor Zinc Sulfide-Quantum Dots (ZnS-QDs), Zn1-xLaxS, were effectively produced via a straightforward co-precipitation approach, with diverse La ratios (0.00 ≤ x ≤ 0.15 at%). The phase analysis of the acquired QDs, conducted through Raman analysis and X-ray diffractometer (XRD), revealed a singular cubic ZnS structure, devoid of any impurities. Morphology studies by HR-TEM showed a nearly spherical particle with a size of approximately 6.4 nm. X-ray photoelectron spectroscope (XPS) investigation disclosed the significant presence of sulfur vacancies, along with the existence of the trivalent oxidation state of lanthanum (La3+) within the ZnS structure. Optical absorbance studies exhibited that all QDs were positioned approximately at the absorption edges of around 270 nm (4.59 eV), surpassing the bulk ZnS energy gap of 337 nm (3.67 eV), harmonically with the quantum confinement effect. Additionally, a pronounced band gap narrowing was observed with increasing the doping level of La ions, on account of the presence of defects that result in the creation of localized states inside the ZnS band structure. The optical results indicated the capability to fine-tune the optical energy gap, dispersion parameters, and enhance the nonlinear optical parameters, which makes these QDs well-suited for use in optoelectronic devices. Furthermore, the photoluminescence (PL) spectra indicated that the La3+-doped ZnS nanocrystals (NCs) exhibited a wide visible emission band (blue emission) at room temperature, influenced by the La-doping concentration. Besides, the La3+-doped ZnS QDs elucidated ferromagnetic behavior at room temperature, which may be accredited to the vacancy-assisted bound magnetic polaron model. Exploring the intriguing magnetic features of ZnS: La3+ QDs could open avenues for developing innovative spintronic devices.

M3XSe4 (M = V, Cr; X = S, Te) monolayers: Intrinsic high-temperature ferromagnetic semiconductors and half metals

Creating low dimensional ferromagnetic (FM) semiconductors or half metals with strong FM orders is promising to meet the requirement for next-generation spintronics. However, most of the demonstrated FM semiconductors or half metals suffer from low Curie temperatures (TCs). Here, by first-principles calculations, we predict that the two-dimensional (2D) M3XSe4 (M = V, Cr; X = S, Te) monolayers are a type of intrinsic 2D ferromagnets with thermodynamical stability. Our results show that V3XSe4 (X = S, Te) monolayers are FM semiconductors with indirect bandgaps of 0.60 and 0.50 eV, respectively. Particularly, both structures are revealed to have high TCs of 387 and 770 K and suppress the application limit of room-temperature. In addition, Cr3XSe4 (X = S, Te) monolayers are FM half metals with 100% spin-polarized currents. Moreover, the electronic and magnetic properties of these M3XSe4 monolayers can be modulated by biaxial strains. V3TeSe4 monolayer can be tuned to be room temperature direct bandgap semiconductor under biaxial 1% tensile strain, and TC of V3SSe4 can be largely enhanced under compressive strains. Our results suggest that M3XSe4 monolayers are promising candidates for spintronic devices.

Two-dimensional Cr2Cl3S3 Janus magnetic semiconductor with large magnetic exchange interaction and high-TC

Abstract The two-dimensional (2D) Janus monolayers are promising in spintronic device application due to their enhanced magnetic couplings and Curie temperatures. Van der Waals CrCl3 monolayer has been experimentally proved to have an in-plane magnetic easy axis and a low Curie temperature of 17 K, which will limit its application in spintronic devices. In this work, we propose a new Janus monolayer Cr2Cl3S3 based on the first principles calculations. The phonon dispersion and elastic constants confirm that Janus monolayer Cr2Cl3S3 is dynamically and mechanically stable. Our Monte Carlo simulation results based on magnetic exchange constants reveal that Janus monolayer Cr2Cl3S3 is an intrinsic ferromagnetic semiconductor with T C of 180 K, which is much higher than that of CrCl3 due to the enhanced ferromagnetic coupling caused by S substitution. Moreover, the magnetic easy axis of Janus Cr2Cl3S3 can be tuned to the perpendicular direction with a large magnetic anisotropy energy (MAE) of 142 μeV/Cr. Furthermore, the effect of biaxial strain on the magnetic property of Janus monolayer Cr2Cl3S3 is evaluated. It is found that the Curie temperature is more robust under tensile strain. This work indicates that the Janus monolayer Cr2Cl3S3 presents increased Curie temperature and out-of-plane magnetic easy axis, suggesting greater application potential in 2D spintronic devices.

Template Selection Strategy for Synthesis of One-Dimensional CrSbSe3 Ferromagnetic Semiconductor Nanoribbons.

CrSbSe3─the only experimentally validated one-dimensional (1D) ferromagnetic semiconductor─has recently attracted significant attention. However, all reported synthesis methods for CrSbSe3 nanocrystals are based on top-down methods. Here we report a template selection strategy for the bottom-up synthesis of CrSbSe3 nanoribbons. This strategy relies on comparing the formation energies of potential binary templates to the ternary target product. It enables us to select Sb2Se3 with the highest formation energy, along with its 1D crystal structure, as the template instead of Cr2Se3 with the lowest formation energy, thereby facilitating the transformation from Sb2Se3 to CrSbSe3 by replacing half of the Sb atoms in Sb2Se3 with Cr atoms. The as-prepared CrSbSe3 nanoribbons exhibit a length of approximately 5 μm, a width ranging from 80 to 120 nm, and a thickness of about 5 nm. The single CrSbSe3 nanoribbon presents typical semiconductor behavior and ferromagnetism, confirming the intrinsic ferromagnetism in the 1D CrSbSe3 semiconductor.

Structural, optical, magnetic, and photocatalytic degradation characteristics of Co0.5Ni0.5Fe2O4 nanoparticles synthesized by plasma arc discharge process

Co0.5Ni0.5Fe2O4 nanoparticles were prepared by the plasma arc discharge method under arc currents of 200, 300, and 400 A in an air atmosphere. The XRD patterns reveal the formation of a single-phase cubic spinel. According to FESEM results, the average particle size in all powders is less than 100 nm. X-ray elemental mapping data confirms the homogeneous composition of the as-synthesized powders. The magnetic and optical data demonstrate a primarily soft ferromagnetic semiconductor behavior, characterized by a saturation magnetization ranging from 62 to 83 emu/g and a band gap energy between 1.86 and 2.15 eV. The photocatalytic activity of the powders synthesized using a 200 A arc, which possesses the lowest band gap energy of 1.86 eV, was assessed by conducting photodegradation experiments on the dyes congo red, methylene blue, and malachite green under UV irradiation in the presence and absence of H2O2. After 105 min of irradiation, the photocatalytic efficiencies of the powders without H2O2 were determined to be 29 %, 57 %, and 83 % for congo red, methylene blue, and malachite green dyes, respectively. However, in the presence of H2O2, the efficiencies significantly increase to 91 %, 95 %, and 96 % for the respective dyes.

Characterization of ferromagnetic semiconductors and valley polarization in janus VBXS2(X = N, P) monolayers

The manipulation of the valley degree of freedom has attracted increasing attention in both fundamental scientific research and emerging applications. Here, we employ first-principles calculations to investigate the structural stability and electronic properties of Janus monolayers of VBXS2 (X=N, P). These materials exhibit characteristics of ferromagnetic semiconductors, with their valence band maximum located at the K/K′ point. Due to the combined effects of inversion symmetry breaking and time reversal symmetry breaking, VBNS2 and VBPS2 exhibit exotic spontaneous valley polarization in their top valence bands, measured at magnitudes of 48.6 meV and 47.6 meV, respectively. Consequently, this phenomenon potentially enables the observation of the anomalous valley Hall effect (AVHE). The unique electronic and valleytronic properties exhibited by Janus VBXS2 suggest a feasible experimental avenue for exploring ferrovalley (FV) and valley-related Hall effects within a two dimensional lattice.

Prediction of Two-Dimensional Janus Transition-Metal Chalcogenides: Robust Ferromagnetic Semiconductor with High Curie Temperature.

Two-dimensional (2D) ferromagnetic semiconductors (FM SCs) provide an ideal platform for the development of quantum information technology in nanoscale devices. However, many developed 2D FM materials present a very low Curie temperature (TC), greatly limiting their application in spintronic devices. In this work, we predict two stable 2D transition metal chalcogenides, V3Se3X2 (X = S, Te) monolayers, by using first-principles calculations. Our results show that the V3Se3Te2 monolayer is a robust bipolar magnetic SC with a moderate bandgap of 0.53 eV, while V3Se3S2 is a direct band-gap FM SC with a bandgap of 0.59 eV. Interestingly, the ferromagnetisms of both monolayers are robust due to the V-S/Se/Te-V superexchange interaction, and TCs are about 406 K and 301 K, respectively. Applying biaxial strains, the FM SC to antiferromagnetic (AFM) SC transition is revealed at 5% and 3% of biaxial tensile strain. In addition, their high mechanical, dynamical, and thermal stabilities are further verified by phonon dispersion calculations and ab initio molecular dynamics (AIMD) calculations. Their outstanding attributes render the V3Se3Y2 (Y = S, Te) monolayers promising candidates as 2D FM SCs for a wide range of applications.

Giant tunnel magnetoresistance in in-plane magnetic tunnel junctions based on the heterointerface-induced half-metallic 2H-VS[formula omitted]

Magnetic tunnel junctions (MTJs) constructed from atomically thin two-dimensional (2D) magnetic materials have attracted great attention in recent years because it meets the requirements of miniaturization and high tunability of next-generation spintronic devices. In this work, we demonstrate that the ferromagnetic semiconductor VS2 is transformed into a half-metal in VS2/MoSSe vdW heterostructure. Based on the heterostructure, we design an in-plane MTJs that comprise a monolayer VS2 barrier sandwiched between two VS2/MoSSe heterostructure electrodes. Through density functional calculations combined with a nonequilibrium Green’s function technique, it is found that the tunnel magnetoresistance (TMR) ratio as high as 4.35 × 109% can be achieved. Moreover, the TMR ratio can be tuned by the barrier length, and the maximum value exceeds 1015%. These results not only provide a novel route for designing MTJs using 2D ferromagnetic semiconductor material, but also demonstrate the great importance of vdW heterostructures in the design of spintronic devices.

Heavily Fe-doped quaternary-alloy ferromagnetic semiconductor (In,Ga,Fe)Sb

We study epitaxial growth and physical properties of heavily Fe-doped quaternary-alloy ferromagnetic semiconductor (In0.84−x ,Ga x ,Fe0.16)Sb thin films (Ga content x = 2%–10%, Fe content fixed at 16%). The (In0.84−x ,Ga x ,Fe0.16)Sb films have a zinc-blende-type crystal structure without any other second phase, and all the samples exhibit intrinsic ferromagnetism with high Curie temperature (>300 K). The carrier type of the (In0.84−x ,Ga x ,Fe0.16)Sb films is found to change by varying x, and a carrier-type phase diagram of (In,Ga,Fe)Sb is presented. These results suggest that (In,Ga,Fe)Sb is a promising material for semiconductor spintronic devices, such as ferromagnetic p-n junctions, operating at RT.

Spin-dependent interactions in orbital-density-dependent functionals: Noncollinear Koopmans spectral functionals

The presence of spin-orbit coupling or noncollinear magnetic spin states can have dramatic effects on the ground-state and spectral properties of materials, in particular on the band structure. Here, we develop noncollinear Koopmans-compliant functionals based on Wannier functions and density-functional perturbation theory, targeting accurate spectral properties in the quasiparticle approximation. Our noncollinear Koopmans-compliant theory involves functionals of four-component orbital densities that can be obtained from the charge and spin-vector densities of Wannier functions. We validate our approach on four emblematic nonmagnetic and magnetic semiconductors where the effect of spin-orbit coupling goes from small to very large: the III-IV semiconductor GaAs, the transition-metal dichalcogenide WSe2, the cubic perovskite CsPbBr3, and the ferromagnetic semiconductor CrI3. The predicted band gaps are comparable in accuracy to state-of-the-art many-body perturbation theory and include spin-dependent interactions and screening effects that are missing in standard diagrammatic approaches based on the random phase approximation. While the inclusion of orbital- and spin-dependent interactions in many-body perturbation theory requires self-screening or vertex corrections, they emerge naturally in the Koopmans-functionals framework. Published by the American Physical Society 2024

Spin-Phonon Coupling and Magnetic Transition in an Organic Molecule Intercalated Cr2Ge2Te6.

The manipulation of spin-phonon coupling in both formations and explorations of magnetism in two-dimensional van der Waals ferromagnetic semiconductors facilitates unprecedented prospects for spintronic devices. The interlayer engineering with spin-phonon coupling promises controllable magnetism via organic cation intercalation. Here, spectroscopic evidence reveals the intercalation effect on the intrinsic magnetic and electronic transitions in quasi-two-dimensional Cr2Ge2Te6 using tetrabutyl ammonium (TBA+) as the intercalant. The temperature evolution of Raman modes, Eg3 and Ag1, along with the magnetization measurements, unambiguously captures the enhancement of the ferromagnetic Curie temperature in the intercalated heterostructure. Moreover, the Eg4 mode highlights the increased effect of spin-phonon interaction in magnetic-order-induced lattice distortion. Combined with the first-principle calculations, we observed a substantial number of electrons transferred from TBA+ to Cr through the interface. The interplay between spin-phonon coupling and magnetic ordering in van der Waals magnets appeals for further understanding of the manipulation of magnetism in layered heterostructures.