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Magnetic semiconductors, with integrated properties of ferromagnets and semiconductors, are significant for developing next-generation spintronic devices. Herein two atomically precise clusters of dysprosium(III) tellurides, formulated respectively as [Na 2 (15-crown-5) 3 (py) 2 ][(η 5 -Cp*Dy) 5 (Te) 6 ](py) 4 (Dy 5 Te 6 , Cp*=pentamethylcyclopentadienyl; py=pyridine) and [K(2,2,2-cryptand)] 2 [(η 5 -Cp*Dy) 6 (Te 3 )(Te 2 ) 2 (Te) 3 ] (Dy 6 Te 10 ), are reported. Crystallographic studies revealed the presence of multifarious tellurido ligands within the polyhedral cluster cores. Spectroscopic and magnetic studies showed that both clusters are single-molecule magnets exhibiting slow magnetic relaxation behaviors at low temperatures and semiconductors with low optical band gaps comparable to benchmark semiconductors. These clusters represent probably the first lanthanide-based molecular magnetic semiconductors., (© 2024 Wiley-VCH GmbH.)

Oxygen in solids usually exists in an O 2- 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 Sr 2 AlO 4 , leading to an intrinsic p-orbital ferromagnetism stable until ≈900 K. Experimental and theoretical investigations have clarified that one-fourth of the oxygen atoms in Sr 2 AlO 4 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., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Over the past five years, significant progress has been made in understanding the magnetism and electronic properties of CaAl 2 Si 2 -type Eu M 2 X 2 ( M = Zn, Cd; X = P, As) compounds. Prior theoretical work and experimental studies suggested that EuCd 2 As 2 had the potential to host rich topological phases, particularly an ideal magnetic Weyl semimetal state when the spins are polarized along the c axis. However, this perspective is challenged by recent experiments utilizing samples featuring ultra-low carrier densities, as well as meticulous calculations employing various approaches. Nonetheless, the Eu M 2 X 2 family still exhibit numerous novel properties that remain to be satisfactorily explained, such as the giant nonlinear anomalous Hall effect and the colossal magnetoresistance effect. Moreover, Eu M 2 X 2 compounds can be transformed from semiconducting antiferromagnets to metallic ferromagnets by introducing a small number of carriers or applying external pressure, and a further increase in the ferromagnetic transition temperature can be achieved by reducing the unit cell volume. These features make the Eu M 2 X 2 family a fertile platform for studying the interplay between magnetism and charge transport, and an excellent candidate for applications in spintronics. This paper presents a comprehensive review of the magnetic and transport behaviors of Eu M 2 X 2 compounds with varying carrier densities, as well as the current insights into these characteristics. An outlook for future research opportunities is also provided., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Utilizing pulsed laser deposition, a film of EuO 1- x was deposited onto a Si(001) substrate with MgO buffer and compared to the same heterostructure with an additional BaTi 2 O 5 thin film on top of the EuO 1- x surface. X-ray diffraction (XRD) indicates the films crystallize into a preferred EuO(111) orientation; it also reveals the clear presence of EuSi 2, which suggests Si or Eu diffuses across the MgO buffer layer. EuO 1- x films exhibit a ferromagnetic (FM) signature and temperature-dependent exchange bias, indicated by MOKE measurements, suggesting the presence of a magnetic order well above the EuO Curie temperature with possible origins in charge carrier density near the interface. In comparison, an antiferromagnetic character persists well above the EuO Curie temperature of 69 K and the enhanced Curie temperature of 150 K for BaTi 2 O 5 films grown on the EuO 1- x films. The antiferromagnetic behavior is not seen in thicker EuO 1- x thin films when integrated with other ferroelectric (FE) phases of the BaO-TiO 2 system, suggesting an origin in the perturbed charge population at the BaTi 2 O 5 /EuO 1- x interface.

Atomic-level defects in van der Waals (vdW) materials are essential building blocks for quantum technologies and quantum sensing applications. The layered magnetic semiconductor CrSBr is an outstanding candidate for exploring optically active defects because of a direct gap, in addition to a rich magnetic phase diagram, including a recently hypothesized defect-induced magnetic order at low temperature. Here, we show optically active defects in CrSBr that are probes of the local magnetic environment. We observe a spectrally narrow (1 meV) defect emission in CrSBr that is correlated with both the bulk magnetic order and an additional low-temperature, defect-induced magnetic order. We elucidate the origin of this magnetic order in the context of local and nonlocal exchange coupling effects. Our work establishes vdW magnets like CrSBr as an exceptional platform to optically study defects that are correlated with the magnetic lattice. We anticipate that controlled defect creation allows for tailor-made complex magnetic textures and phases with direct optical access.

The search and design of two-dimensional (2D) magnetic semiconductors for spintronics applications are particularly significant. In this work, we investigated the electronic and magnetic properties of Janus structure based on Dirac half-metallic vanadium phosphide (VP) monolayer (ML) by first-principles calculations. Due to the vertical symmetry breaking, Janus V 2 AsP ML becomes an intrinsic ferromagnetic semiconductor with a narrow band gap of 0.21 eV. We analyzed the electronic structure and origin of the in-plane easy axis in Janus V 2 AsP. The electron effective mass is anisotropic and only 0.129 m 0 along the x -direction. The Curie temperatureTcand magnetic anisotropy energy (MAE) of Janus V 2 AsP reach 490 K and 178  µ eV per V atom, respectively. A uniaxial tensile stain ɛ x of 5% can increase its band gap and MAE to 0.39 eV and 210.6  µ eV per V atom while maintaining itsTcbeing above room temperature. Moreover, the direction of the easy axis can be changed between the in-plane x - and y -direction by a small uniaxial tensile strain ɛ x of 2%. Our study can motivate further research on the design the magnetic semiconductors in Janus structures based on 2D Dirac half-metals for spintronics applications., (© 2022 IOP Publishing Ltd.)

A 2D van der Waals (vdW) magnet can get rid of the constraints of lattice matching and compatibility and then create a variety of vdW heterostructures, which provides a opportunity for spintronic devices. However, the ability to reliably exfoliate large, high-quality vdW ferromagnetic Fe 3 GeTe 2 (FGT) nanoflakes in scaled-up production is severely limited. Herein, an efficient and stable three-stage sonication-assisted liquid-phase exfoliation was developed for mass preparation of high-structural-integrity few- and single-layer FGT nanoflakes with a greatly enhanced intrinsic exchange bias. The three stages include slicing crystals, weakening interlayer vdW forces, and using ultrasonic cavitation. The highest yield of FGT nanoflakes is 22.3 wt % with single layers accounting for 6%. The size is controllable, and several micrometers, tens of micrometers, and a maximum of 103 μm are available. The 200 mg level output has overcome the limitations of mechanical exfoliation and molecular beam epitaxy in economically amplificated production. An intrinsic exchange bias is observed in the restacked nanoflakes due to the magnetic proximity on the interface of the FGT/natural surface oxide layer. The material reaches 578 Oe (2 K) and 2300 Oe after further oxidation, at least 250% higher than other precisely tailored vdW magnetic heterostructures. In addition, the unusual semiconductivity of the liquid-phase exfoliated FGT nanoflakes is reported. This work skillfully utilizes oxidation to enhance the potential of FGT for large-scale spintronics, optoelectronics, efficient data storage, and various extended applications, and it is beneficial for exfoliating other promising magnetic vdW materials.

Ultrathin layered crystals of coordinated chromium(III) are promising not only as two-dimensional (2D) magnets but also as 2D near-infrared (NIR) emitters due to long-range spin correlation and efficient transition between high- and low-spin excited states of Cr 3+ ions. In this study, we report on the dual-band NIR photoluminescence (PL) of CrPS 4 and show that its excitonic emission bifurcates into fluorescence and phosphorescence depending on thickness, temperature, and defect density. In addition to the spectral branching, the biexponential decay of PL transients, also affected by the three factors, could be well described within a three-level kinetic model for Cr(III). In essence, the PL bifurcations are governed by activated reverse intersystem crossing from the low- to high-spin states, and the transition barrier becomes lower for thinner 2D samples because of surface-localized defects. Our findings can be generalized to 2D solids of coordinated metals and will be valuable in realizing groundbreaking magneto-optic functions and devices.

The advent of two-dimensional (2D) magnets offers unprecedented control over electrons and spins. A key factor in determining exchange coupling and magnetic order is symmetry. Here, we apply second harmonic generation (SHG) to probe a 2D magnetic semiconductor CrSBr. We find that monolayers are ferromagnetically ordered below 146 K, an observation enabled by the discovery of a large magnetic dipole SHG effect in the centrosymmetric structure. In multilayers, the ferromagnetic monolayers are coupled antiferromagnetically, and in contrast to other 2D magnets, the Néel temperature of CrSBr increases with decreasing layer number. We identify magnetic dipole and magnetic toroidal moments as order parameters of the ferromagnetic monolayer and antiferromagnetic bilayer, respectively. These findings establish CrSBr as an exciting 2D magnetic semiconductor and extend the SHG probe of magnetic symmetry to the monolayer limit, opening the door to exploring the applications of magnetic-electronic coupling and the magnetic toroidal moment.

Various mechanisms of electrical generation of spin polarization in nonmagnetic materials have been a subject of broad interest for their underlying physics and device potential in spintronics. One such scheme is chirality-induced spin selectivity (CISS), with which structural chirality leads to different electric conductivities for electrons of opposite spins. The resulting effect of spin filtering has been reported for a number of chiral molecules assembled on different surfaces. However, the microscopic origin and transport mechanisms remain controversial. In particular, the fundamental Onsager relation was argued to preclude linear-response detection of CISS by a ferromagnet. Here, we report definitive observation of CISS-induced magnetoconductance in vertical heterojunctions of (Ga,Mn)As/AHPA-L molecules/Au, directly verifying spin filtering by the AHPA-L molecules via spin detection by the (Ga,Mn)As. The pronounced and robust magnetoconductance signals resulting from the use of a magnetic semiconductor enable a rigorous examination of its bias dependence, which shows both linear- and nonlinear-response components. The definitive identification of the linear-response CISS-induced two-terminal spin-valve effect places an important constraint for a viable theory of CISS and its device manifestations. The results present a promising route to spin injection and detection in semiconductors without using any magnetic material.

Many two-dimensional (2D) semiconductors represented by transition metal dichalcogenides have tunable optical bandgaps in the visible or near IR-range standing as a promising candidate for optoelectronic devices. Despite this potential, however, their photoreactions are not well understood or controversial in the mechanistic details. In this work, we report a unique thickness-dependent photoreaction sensitivity and a switchover between two competing reaction mechanisms in atomically thin chromium thiophosphate (CrPS 4 ), a two-dimensional antiferromagnetic semiconductor. CrPS 4 showed a threshold power density 2 orders of magnitude smaller than that for MoS 2 obeying a photothermal reaction route. In addition, reaction cross section quantified with Raman spectroscopy revealed distinctive power dependences in the low and high power regimes. On the basis of optical in situ thermometric measurements and control experiments against O 2 , water, and photon energy, we proposed a photochemical oxidation mechanism involving singlet O 2 in the low power regime with a photothermal route for the other. We also demonstrated a highly effective encapsulation with Al 2 O 3 as a protection against the destructive photoinduced and ambient oxidations.

Local manipulation of the magnetization direction is of significant importance in spintronics because it provides an effective way in nonvolatile device applications for ultrahigh density information storage. However, this modulation is usually restricted to a limited range even through large power input. We demonstrate a large rotation of the magnetization vector in a magnetic semiconductor (Ga,Mn)As (110) thin film by surface decoration of self-assembled molecules. The carrier density of the film is vastly changed by two kinds of molecules acting as electron donors and acceptors, resulting in a prominent variation of the Curie temperature and magnetic anisotropy. The magnetic anisotropic fields tuned by the molecules could be quantitatively determined by planar Hall measurements, based on which the largest rotation angle is calculated to be ∼27°. This value doubles the result obtained by the electric field up to 0.4 V/nm, which is approaching the breakdown strength of common dielectrics. Our work offers a new functionality for effectively tuning the magnetization direction of nanoscale bits, without relying on the magnetic field, spin current, or mechanical strain.

Using first principles calculations, we explored the magnetic and optical properties of chromium(III) iodide (CrI₃) nanotubes (NTs) by changing their chirality and diameter. Here, we considered six types of NTs: (5,0), (5,5), (7,0), (10,0), (10,10), and (12,0) NTs. We found that both zigzag and armchair NTs had a ferromagnetic ground with a direct band gap, although the band gap was dependent on the chirality and diameter. Using the Monte Carlo simulation, we found that the Curie temperatures (T c ) exhibited chirality and diameter dependence. In zigzag NTs, the larger the tube diameter, the larger the T c , while it decreased with increasing diameter in the armchair tube. We found that the T c was almost doubled when the diameter increased two-fold. This finding may guide development of room temperature ferromagnetism in zigzag NTs. We also found that the CrI₃ NTs displayed anisotropic optical properties and anomalous optical dispersion in the visible range. Specifically, the (10,0) zigzag NT had a large refractive index of 2 near the infrared region, while it became about 1.4 near blue light wavelengths. We also obtained large reflectivity in the ultraviolet region, which can be utilized for UV protection. Overall, we propose that the CrI₃ NTs have multifunctional physical properties for spintronics and optical applications.

Practical applications of semiconductor spintronic devices necessitate ferromagnetic behavior at or above room temperature. In this paper, we demonstrate a two-dimensional manganese gallium nitride surface structure (MnGaN-2D) which is atomically thin and shows ferromagnetic domain structure at room temperature as measured by spin-resolved scanning tunneling microscopy and spectroscopy. Application of small magnetic fields proves that the observed magnetic domains follow a hysteretic behavior. Two initially oppositely oriented MnGaN-2D domains are rotated into alignment with only 120 mT and remain mostly in alignment at remanence. The measurements are further supported by first-principles theoretical calculations which reveal highly spin-polarized and spin-split surface states with spin polarization of up to 95% for manganese local density of states.

Thermoelectrics (TE), the direct solid-state conversion of waste heat to electricity, is a promising field with potential wide-scale application for power generation. Intrinsic conflicts in the requirements for high electrical conductivity but (a) low thermal conductivity and (b) a large Seebeck coefficient have made enhancing TE performance difficult. Several recent striking advances in the field are reviewed. In regard to the former conflict, notable bottom-up nanostructuring methods for phonon-selective scattering are discovered, namely using nanosheets, dislocations, and most strikingly a process to fabricate nano-micropores leading to a 100% enhancement in the figure of merit (ZT ≈ 1.6) for rare-earth-free skutterudites. Porous materials are hitherto considered as having poor TE performance, so this is a new paradigm. In regard to the latter conflict, nanocomposite materials with hybrid effects and use of magnetism are emerging as novel bottom-up methods to enhance TE. Material informatics efforts to identify high-ZT materials are also reviewed., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Biocompatible magnetic semiconductor Zn 1-x Mg x Fe 2 O 4 (x=0, 0.1, 0.3, 0.5 & 0.7) nanoparticles of around 10nm diameter were synthesized by solvothermal reflux method. The method produces well separated and narrow size distributed nanoparticles. Crystal structure, morphology, particles surface properties, surfactant quantity, colloidal stability, magnetic properties and photocatalytic properties of the synthesized nanoparticles were studied. Different characterizations confirmed that all compounds were single crystals and superparamagnetic at room temperature. Saturation mass magnetization (M s =57.5emu/g) enhances with substituent Mg 2+ concentration due to promotion of mixed spinel (normal and inverse) structure. Photocatalytic activity of all synthesized magnetic semiconductor nanoparticles were studied through methylene blue degradation. The degradation of 98% methylene blue was observed on 60 min irradiation of light. It is observed that photocatalytic activity slightly enhances with substituent Mg 2+ concentration. The synthesized biocompatible magnetic semiconductor nanoparticles can be utilized as photocatalysts and could also be recycled and separated by applying an external magnetic field., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A few years ago, it was claimed that the two-dimensional (2D) feroxyhyte (δ-FeOOH) layer could possess a net magnetic moment and it could be applied for potential spintronics applications because it showed a band gap. However, the exact crystal structure is still unknown. Hereby, we investigate the crystal structure, electronic band structure, and magnetic and optical properties of 2D δ-FeOOH using density functional calculations. On the basis of the experimental observation and dynamical stability calculations, we propose that the 2D δ-FeOOH originates from bulk Fe(OH) 2 via oxidation. A perfect antiferromagnetic ground state was observed in the monolayer structure with an indirect band gap of 2.4 eV. On the other hand, the bilayer structure displayed a direct band gap of 0.87 eV, and we obtained a ferrimagnetic state. The net magnetic moment in the bilayer was 1.49 μ B per cell. The interlayer distance and film thickness in bilayer δ-FeOOH were 1.68 and 7.37 Å, respectively. This interlayer distance was suppressed to 1.47 Å in a trilayer system, and the band gap of 1.6 eV was found. The trilayer δ-FeOOH had a film thickness of 11.57 Å, and this is comparable to the experimental thickness of 12 Å. To compare with the experimental band gap of 2.2 eV obtained from a UV-visible optical spectrum measurement, we also calculated the absorption spectra, and the onset of the absorption peak in the monolayer, bilayer, and trilayer appeared at 3.2, 2.8, and 2.2 eV, respectively. Overall, considering the magnetic state, optical absorption, and film thickness, we propose that the trilayer structure agrees with the experimentally synthesized structure.

The search for emerging materials combining magnetic and semiconducting properties has attracted widespread interest in contemporary materials science. Chalcopyrite (CuFeS2), as an earth abundant and nontoxic chalcogenide compound in the I-III-VI2 family, is a promising class of such materials that exhibit unusual electrical, optical, and magnetic properties. However, its successful implementation largely depends on our ability to understand, control and manipulate their structural, transport and spin behavior. Here we show that solution processing monodispersed CuFeS2 quantum dots exhibit a strong coupling among optical, electronic, and magnetic degrees of freedom. The photoresponse and magnetoconductance of CuFeS2 quantum dots are realized under external stimuli. We further exploit a fast and efficient way to achieve an exceptionally large performance in a magneto-optoelectronic hybrid system consisting of magnetic semiconducting CuFeS2 and conducting polymer matrix. The results demonstrate a promising potential of magnetic semiconductor CuFeS2 in the field of spin electronics.