Ferromagnetic Semiconductor Research Articles

Abstract Room temperature ferromagnetic ZnO thin magnetic semiconductor material can solve the problems of large electronic component volume and low integration density in traditional semiconductors. In this paper, direct and precipitation methods were used for the hydrothermal synthesis of Zn1-xMnxO (x = 0.05) crystals. The hydrothermal reaction conditions were 1 mol/L KOH or NaOH as mineralizers, and the reaction time was 24 hours at 180 °C. XRD measured the phase in the crystal and confirmed that Mn ions can be doped in ZnO, but the doping amount is limited. SEM displays the morphology of crystals, and the morphology of doped crystals synthesized under different processes varies. NaOH is more suitable as a mineralizer for Mn-doped ZnO than KOH. The powder distribution obtained by the direct precipitation method is more uniform and the dispersion is better than that obtained by a direct method, indicating that the direct precipitation method is more suitable as a precursor preparation method for Mn-doped ZnO.

ABSTRACTRoom‐temperature organic ferromagnetic semiconductors represent a promising frontier in developing next‐generation electronic and spintronic devices. However, the origin of magnetic moments in organic ferromagnets and the acquisition of critical evidence for magnetic ordering remain incompletely understood. This study presents compelling evidence for room‐temperature ferromagnetism in N,N′‐diamino perylene bisimide (2NH2‐PBI) radical aggregates through a comprehensive analysis utilizing X‐ray magnetic circular dichroism (XMCD), low‐field microwave absorption (LFMA) techniques and magnetic characterization. The 2NH2‐PBI samples, prepared via hydrothermal reduction, exhibit a significant saturation magnetization of 0.8 emu g−1 (336.3 emu mol−1) at 300 K, with a coercive field of 170 Oe. The XMCD measurements at the carbon K‐edge exhibited a pronounced dichroic signal (~8.7%), confirming the origin of ferromagnetism in the π‐conjugated electrons of the perylene core. Density functional theory calculations further support this finding by demonstrating that spin density is primarily delocalized on the π‐conjugated skeleton, giving a microscopic explanation for the magnetic properties of 2NH2‐PBI radicals. Furthermore, LFMA studies provide additional evidence of ferromagnetic ordering, showcasing hysteretic behavior consistent with domain wall dynamics. Our work indicates that imide‐based radical molecules with extended π‐conjugated structures constitute a class of effective magnetic functional units.

Two-dimensional (2D) magnetic materials have flourished to date, with ferromagnetic (FM) materials providing a broad platform for exploring the novel quantum anomalous Hall (QAH) effect. However, the extremely low working temperature in most QAH candidates significantly limits the experimental realization. Herein, we designed a series of transition metal chalcogenide VX2 (X = S, Se, Te) monolayers using first-principles calculations and investigated their electronic and topological properties. The results indicate that all these materials are dynamically stable FM 2D materials. Notably, VTe2 is identified as an intrinsic room-temperature QAH insulator with the Chern number of C = 1 and a sizable bandgap of 0.14 eV. This large bandgap arises from the band inversion between the spin-up bands contributed by the px and py orbitals of Te atoms. Additionally, VTe2 exhibits a Curie temperature of 444 K, exceeding the room temperature. VS2 and VSe2 monolayers are FM semiconductors whose electronic properties can be turned by applying external strains. Among them, the VSe2 monolayer becomes a QAH insulator with C = 1 under suitable biaxial compressive strains. This study introduces a category of QAH candidates that show significant promise for implementation in spintronic devices.

ABSTRACTBuilding van der Waals heterostructure is an effective method to design multiferroic materials. Here, by performing first principles calculations, we study the electronic and magnetic properties of CuCrP2S6/CuInP2S6 (CCPS/CIPS) heterostructure composed of ferroelectric (FE) CuInP2S6 and multiferroic CuCrP2S6. It is shown that CCPS‐P↓/CIPS‐P↓ is a ferromagnetic (FM) half metal, with the band alignment of type II in the spin‐down channel, while for CCPS‐P↑/CIPS‐P↑, CCPS‐P↑/CIPS‐P↓, and CCPS‐P↓/CIPS‐P↑, they are all FM semiconductors with type II band alignment. Moreover, the electronic properties of CCPS/CIPS can be changed under biaxial strains; that is, CCPS‐P↓/CIPS‐P↓ can change from FM half metal to FM semiconductor, and CCPS‐P↑/CIPS‐P↑, CCPS‐P↑/CIPS‐P↓, and CCPS‐P↓/CIPS‐P↑ have shrinking band gaps in both spin channels under biaxial strains. Such characteristics suggest CCPS/CIPS heterostructure can be potential nonvolatile memory device materials.

Anomalous valley Hall effect (AVHE) in two-dimensional materials represents a cornerstone phenomenon in condensed matter physics. While substantial research efforts have been predominantly concentrated on d-orbital systems, its realization in p-orbital platforms is rarely investigated. Here, taking monolayer XN (X = Ge and Sn) as prototypical systems, we demonstrate the existence of AVHE in two-dimensional p-orbital systems through first-principles calculations and symmetry analysis. Monolayer XN is a ferromagnetic semiconductor with a pair of valleys in the valence bands. The synergistic breaking of both inversion and time-reversal symmetries enables spin–orbit coupling to intrinsically lift the valley degeneracy, yielding spontaneous valley polarizations. Moreover, the emergent valley-contrasting Berry curvatures directly manifest measurable AVHE responses under in-plane electric fields. Crucially, we systematically elucidate the microscopic origin of these polarization phenomena, uncovering the essential role of in-plane px/y orbital contribution. These findings significantly expand the candidate materials for valleytronic research.

Synthesized AgVP2Se6, an intrinsic ferromagnetic semiconductor with van der Waals layered structure, has opened possibilities for investigating two-dimensional magnetism and spintronic device applications. Magnetic anisotropy energy (MAE) defines the stability of magnetization in a specific direction with respect to the crystal lattice and is an important parameter for nanoscale applications. Here, we systematically study the MAE of AgVP2Se6 monolayers using carrier doping and biaxial strain, through first-principles calculations. Our computational analysis reveals that carrier doping amplifies the MAE to 0.33 meV/atom. Subsequent synergistic application with biaxial strain further elevates the MAE to 1.72 meV/atom. Orbital-resolved analysis identifies the enhancement mechanism through distinct contributions from V and Ag atoms: ⟨dxy|Lz|dx2−y2⟩ and ⟨dyz|Lx|dz2⟩ orbitals in V atoms cooperate with ⟨dyz|Lz|dxz⟩ and ⟨dyz|Lx|dz2⟩ components from Ag atoms. Additionally, the magnetic exchange interaction is also enhanced under modulation of carrier doping and biaxial strain, the nearest-neighbor exchange constant increases to 1.85 meV. By carrying out Monte Carlo simulations, we predict the Curie temperature (TC) enhanced up to ∼100 K. This work establishes an effective strategy for improving the MAE of AgVP2Se6 and significantly advances its potential for spintronic applications at low temperatures.

Abstract Recently, a new two-dimensional (2D) MoSi2N4 layered material was successfully synthesized [Science 369(2020)670], attracting significant attention from the research community. Following up on this work, we have successfully predicted other three stable MSi2N4 (M=Tm, Pa, Np) monolayers in the 2D MA2Z4 family using the CALYPSO structural prediction method combined with first-principles calculations. The energy band structure calculations show that the TmSi2N4 monolayer is a ferromagnetic (FM) semimetal, and the PaSi2N4 monolayer is a FM metal. In contrast, NpSi2N4 monolayer is a FM semiconductor with Curie temperature of 812 K, which is higher than those of the vast majority of 2D FM semiconductor materials. The Curie temperature of NpSi2N4 monolayer is attributed to the large magnetic moments of Np atoms and the strong exchange coupling interactions between the adjacent Np atoms. Interestingly, the Curie temperature of the NpSi2N4 monolayer can be further enhanced through reasonable modulation of biaxial strain. It is about 1008 K under a biaxial tensile strain of 3%. The present findings deepen our understanding of the structural and magnetic properties of MSi2N4 (M=Tm, Pa, Np) monolayers, and offer important insights for the design and synthesis of multifunctional nanoelectronic devices.

Abstract Efficient spin injection is essential for the development of ferromagnet—semiconductor spintronic devices with high performances, including spin transistors. Although the Co2Fe(Al0.5,Si0.5) (CFAS)/Ge hybrid structure has been identified as an outstanding platform for such devices, there is a lack of systematic analyses on the effects of the interface atomic structure on the spin-electronic properties. In this study, we investigate electronic and magnetic properties of CFAS/Ge (001) interfaces by density functional theory calculations under two possible scenarios, with atomically abrupt bulk-like interfaces and with intermixing at the interfaces. For two possible terminations in the case of abrupt interfaces, we show considerable reductions in spin polarization (SP), which is emphasized in the case of the —Fe—Si,Al/Ge interface, where the SP has reversed sign. Further, we show that Fe—Ge interdiffusion is most likely to occur at the interface, and that this intermixing does not largely affect the spin-electronic properties. In contrast, the model of interdiffusion affecting the Co sublattice in the CFAS film exhibits a reversed SP at the interface layers, but this is less likely to occur owing to the higher energy for such atomic swaps. Band alignment analyses show that interfaces with a small degree of Fe/Ge intermixing could be beneficial for the spin injection efficiency. This study demonstrates that the spin injection efficiency is strongly dependent on the ferromagnet—semiconductor interface atomic structure, and thus can guide further theoretical and experimental studies for development of spintronic devices with improved properties.

As a member of the two-dimensional transition metal trihalide (MX3) family, the MnI3 monolayer has recently garnered significant attention due to its unique intrinsic ferromagnetic half-metallic properties and high Curie temperature. However, its inherent in-plane magnetization preference limits its potential applications in spintronics. To address this issue, in this work, we investigate the effects of 3d transition metal V and Cr doping on the electronic structure and magnetic properties of the MnI3 monolayer. The results show that the doped systems exhibit excellent structural stability and out-of-plane ferromagnetic semiconductor properties. In the VMn2I6 and CrMn2I6 monolayer, the adsorption energy can reach −8.421 and −5.796 eV/atom, respectively, and the large magnetic anisotropy energies flip their easy magnetization axis along the z-direction successfully. Moreover, the semiconductor bandgaps can increase to 2.51 and 1.26 eV relative to half-metal MnI3 monolayer. Bader charge analysis reveals that V and Cr doping enhance charge transfer in the MnI3 monolayer and increase the magnetic moment of Mn ions to approximately 4.6 μB. The interstitial doping significantly changes the exchange interactions path between magnetic atoms, leading to a noticeable reduction in the Curie temperature. This work provides an effective approach and theoretical support for regulating the electronic properties and easy magnetization axis orientation in MnI3 two-dimensional materials.

Two-dimensional robust ferromagnetic semiconductors with intrinsic valley polarization have tremendous potential for applications in next-generation nano-information storage devices. Based on first-principles calculations, we predict that a novel honeycomb family of monolayer h-TiX (X = N, P, As, Sb, and Bi ) is intrinsic ferrovalley materials. The ferromagnetism of monolayer h-TiX is attributed to the dz2 orbitals of Ti atoms, exhibiting a magnetic direction tilted out of the plane. Strain engineering can adjust magnetic properties, including variations in Curie temperature, which primarily respond sensitively to the strain-induced changes in exchange coupling coefficient J to strain. Because of the absence of time-reversal symmetry and inversion symmetry, spontaneous valley polarization phenomenon can be observed in monolayer h-TiN, which can be explained using perturbation theory of spin–orbit coupling. Both the ferromagnetic semiconductors and spontaneous valley polarization can be achieved in h-TiN, which offer a promising candidate material and foundational research value for spintronic devices and valleytronic devices.

Abstract We investigate the carrier, phonon, and spin dynamics in the ferromagnetic semiconductor (In,Fe)Sb using ultrafast optical pump-probe spectroscopy. We discover two anomalies near T *(∼40 K) and T †(∼200 K) in the photoexcited carrier dynamics, which can be attributed to the electron-spin and spin-lattice scattering processes influenced by the magnetic phase transition and modifications in magnetic anisotropy. The magnetization change can be revealed by the dynamics of coherent acoustic phonon. We also observe abrupt changes in the photoinduced spin dynamics near T * and T †, which not only illustrate the spin-related scatterings closely related to the long-range magnetic order, but also reveal the D’yakonov–Perel and Elliott–Yafet mechanisms dominating at temperatures below and above T †, respectively. Our findings provide important insights into the nonequilibrium properties of the photoexcited (In,Fe)Sb.

Ferromagnetic semiconductor CrSiTe3 with a layered honeycomb structure is a promising candidate for the Chern insulator in a monolayer form. However, detecting its topological transport properties is challenging as Dirac nodes are located far above the Fermi level. High pressure, an effective route to control the electronic structure, provides an opportunity to measure its topological transport properties. We find that while CrSiTe3 maintains the honeycomb structure up to ~12 GPa, it undergoes an insulator‒metal transition and a nearly concomitant increase of Curie temperature TC from ~33 to ~85 K at P1 ~ 6 GPa. Furthermore, the saturated magnetization Ms along the c-axis exhibits successive drops from Ms = 3μB/Cr at ambient pressure to ~Ms/2 at P1 and to ~Ms/3 at 9.8 GPa. Notably, between P1 and 13.5 GPa, the anomalous Hall conductivity σxyAH appears below TC and σxyAH at 2 K exhibits a dome-like pressure evolution, reaching a maximum of ~67Ω−1cm−1, ~ 35% of e2/hc, at 10.4 GPa. These results suggest that large σxyAH arises from the intrinsic Berry curvature inherent to the band topology of the pressure-induced ferromagnetic metallic states.

Abstract The structural, energetic, and electronic properties of Mn2S monolayers and their functionalized derivatives were systematically investigated using first-principles calculations. The pristine Mn2S monolayers, existing in the 1T and 2H phases, exhibited metallic characteristics with intrinsic magnetism. However, phonon dispersion analysis reveals dynamic instability in both phases, indicating that pristine Mn2S is not a stable monolayer material. To enhance stability, we examined the effects of oxygen (O), fluorine (F), and chlorine (Cl) functionalization on Mn2S, constructing twelve distinct Mn2ST2 configurations for each phase. The findings demonstrate that functionalization significantly alters the energetic hierarchy, with different configurations emerging as the most stable phase across all functional terminations. Phonon dispersion analysis confirms the dynamical stabilities of the 1T-Mn2SO2, 2H-Mn2SO2, 2H-Mn2SF2, and 1T-Mn2SCl2. Mulliken charge analysis further highlights significant charge redistribution upon functionalization, enhancing charge localization and stability. Among the various Mn2ST2 structures, functionalization plays a crucial role in stabilizing the monolayers. The 1T and 2H phases of Mn2SO2 are identified as the most energetically and dynamically stable configurations, characterized by strong Mn-O bonding and a ferromagnetic half-metallic ground state. In contrast, the most stable form of Mn2SF2 adopts a 2H phase, exhibiting antiferromagnetic ordering and a band gap of 1.617 eV. Additionally, a stabilized 1T-Mn2SCl2 demonstrates ferromagnetic behavior and functions as a ferromagnetic semiconductor with a narrow band gap of 0.196 eV. These findings highlight the critical role of surface functionalization in stabilizing Mn2S monolayers and tailoring their electronic and magnetic properties, paving the way for potential applications in spintronics and nanoelectronics.

Opto-spintronics is an emerging field that focuses on harnessing light to manipulate and analyze electron spins to develop next-generation electronic devices. This paper explores recent progress and the role of solid-state materials in opto-spintronics by focusing on key classes of materials, such as ferromagnetic semiconductors, two-dimensional (2D) transition metal dichalcogenides (TMDCs), and topological insulators. It examines the unique properties of ferromagnetic and antiferromagnetic materials and their ability to interact with light to affect spin dynamics, offering potential for improved sensing and quantum computing. By combining opto-spintronics with solid-state systems, spintronic devices could become faster and more efficient, leading to new technological advancements and scalable technologies.

Metal halide perovskites have attracted extraordinary attention due to their excellent photoelectric properties and diverse crystal structures. The introduction of transition elements through doping serves as a potent strategy to modulate their physical and chemical properties. This approach has proven effective in imparting ferromagnetic semiconductor characteristics, which are essential for applications in spin light-emitting devices and semiconductor spintronics. Here, we synthesized Cs4PbBr6 and Mn-doped Cs4PbBr6 (Mn:Cs4PbBr6) perovskite single crystals. Magnetization measurements reveal that Mn:Cs4PbBr6 exhibits a ferromagnetic behavior at 30 K. Complementary density functional theory calculations suggest that the observed magnetism arises from the introduction of single-spin energy states by the doped Mn in the bandgap. Moreover, we observed a negative photoconductivity (NPC) effect at room temperature in the Mn-doped samples. This NPC phenomenon is attributed to the absorption and desorption of oxygen molecules on the surface of Mn:Cs4PbBr6 crystals. Our findings provide a foundation for the development of highly selective gas sensors in the future.

The newly discovered 2D spin-gapless magnetic materials, which provide new opportunities for combining spin polarization and the quantum anomalous Hall effect, provide a new method for the design and application of memory and nanoscale devices. However, a low Curie temperature (TC) is a common limitation in most 2D ferromagnetic materials, and research on the topological properties of nontrivial 2D spin-gapless materials is still limited. We predict a novel spin-gapless semiconductor of monolayer h-VN, which has a high Curie temperature (~543 K), 100% spin polarization, and nontrivial topological properties. A nontrivial band gap is opened in the spin-gapless state when considering the spin-orbit coupling (SOC); it can increase with the intensity of spin-orbit coupling and the band gap increases linearly with SOC. By calculating the Chern number and edge states, we find that when the SOC strength is less than 250%, the monolayer h-VN is a quantum anomalous Hall insulator with a Chern number C = 1. In addition, the monolayer h-VN still belongs to the quantum anomalous Hall insulators with its tensile strain. Interestingly, the quantum anomalous Hall effect with a non-zero Chern number can be maintained when using h-BN as the substrate, making the designed structure more suitable for experimental implementation. Our results provide an ideal candidate material for achieving the QAHE at a high Curie temperature.

The pursuit of ferromagnetic semiconductors capable of realizing the quantum anomalous hall effect (QAHE) at room temperature holds significant importance for the development and application of spintronic devices. However, current experimental realizations of QAHE in 2D materials are often limited by extremely low TC and minute nontrivial bandgaps. Herein, based on first‐principles calculations, a stable QAHE system that can exist at room temperature is successfully achieved by adsorbing N and O atoms on opposite sides of arsenene. According to the computational results, this novel 2D O─As─N system exhibits ferromagnetic semiconducting behavior with a TC of 350 K and a bandgap of ≈131 meV. Further calculations and analysis of the system's gapless chiral edge states, Chern number (C = 1), and quantized quantum Hall conductivity confirm the topological nontriviality of the bandgap. This work sheds light on the physical mechanisms for developing spintronic devices utilizing room‐temperature ferromagnetic semiconductors and realizing lossless devices through the application of room‐temperature QAHE.

First-principles study on 2D ferromagnetic semiconductor in Janus single-layer CrXY (X = P, As; Y = Cl, Br, I)

The rise of two-dimensional magnets offers a broad research platform for exploring low-dimensional magnetocaloric technology for efficient and green refrigeration applications. Here, we focus on a two-dimensional ferromagnetic semiconductor CrSX (X = F, Cl, Br, I) to investigate its magnetocaloric properties and thermal transport properties along with the underlying physical mechanisms. It is found that CrSX intrinsically possesses a substantial isothermal entropy change (−ΔSmagmax) of 12.3 μJ m−2 K−1 and adiabatic temperature change (ΔTadmax) of 2.3 K during magnetic phase transition. Surprisingly, it exhibits remarkably high thermal conductivity of up to 54.47 W/mK that is attributed to the extended phonon lifetime. Additionally, tensile strain effectively modulates the Curie temperature and refrigerant capacity, with tensile strain weakening direct antiferromagnetic coupling, thus enhancing ferromagnetism. Hole doping efficiently adjusts the magnetic exchange interaction, which enhances the Curie temperature of CrSI to room temperature (305 K) while maintaining a high refrigerant capacity of 180 J/mol under a magnetic field, ascribing to the reduced energy gap between eg orbitals of transition metal cations and p orbitals of nonmagnetic anions. The present work provides insights for understanding the relation between magnetic exchange interactions, thermal transport, and refrigerant performance, offering guidance for designing two-dimensional magnets for magnetocaloric applications.

We perform a comprehensive analysis of the correlated electronic structure reconstruction of the ferromagnetic CrSBr van der Waals (vdW) bulk crystal. Using generalized gradient approximation combined with dynamical mean-field theory, we show the minor role played by multi-orbital electron–electron interactions in semiconducting CrSBr. Our study is relevant to understanding the electronic structure within the Cr3+ oxidation state with strongly spin-polarized t2g orbitals and should be applicable to other ferromagnetic vdW materials from bulk down to the low-dimensional limit. This work is relevant for understanding orbital and spin selectivity and its link to the memristor current–voltage characteristic of CrSBr for future neuromorphic computing.