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Recent success in exfoliating violet or Hittorf's phosphorus down to monolayer reignites the research passion in this ancient yet mysterious material, questing for superior electronic and optoelectronic functionalities. Unfortunately, the poor air stability that plagues black phosphorus also exists in the violet counterpart. Aiming to provide more insight into the degradation chemistry and accordingly find a facile solution for it, herein, we employ concerted elemental, chemical and vibrational spectroscopies to reveal the critical role of oxygen and water in the degradation mechanism and pathway of violet phosphorus in ambient condition. Thereafter, a simple passivation approach by oxide encapsulation is demonstrated to realize air-stable violet phosphorus photodetector device. As the proof-of-concept, the photodetector fabricated accordingly shows superior figures of merit with ultralow dark current (< 10−13 A), high low-light responsivity (6 A W−1) and fast response time (< 10 ms) in the ultraviolet to visible spectrum, as well as great chemical robustness against harsh environments.

Adding ferromagnetism into semiconductors attracts much attentions due to its potential usage of magnetic spins in novel devices, such as spin field-effect transistors. However, it remains challenging to stabilize their ferromagnetism above room temperature. Here we introduce an atomic chemical-solution strategy to grow wafer-size NiO thin films with controllable thickness down to sub-nanometer scale (0.92 nm) for the first time. Surface lattice defects break the magnetic symmetry of NiO and produce surface ferromagnetic behaviors. Our sub-nanometric NiO thin film exhibits the highest reported room-temperature ferromagnetic behavior with a saturation magnetization of 157 emu/cc and coercivity of 418 Oe. Attributed to wafer size, the easily-transferred NiO thin film is further verified in a magnetoresistance device. Our work provides a sub-nanometric platform to produce wafer-size ferromagnetic NiO thin films as atomic layer magnetic units in future transparent magnetoelectric devices.

Kondo effect is an interesting phenomenon in quantum many-body physics. Niobium (Nb) is a conventional superconductor important for many superconducting device applications. It was long thought that the Kondo effect cannot be observed in Nb because the magnetic moment of a magnetic impurity, e.g. iron (Fe), would have been quenched in Nb. Here we report an observation of the Kondo effect in a Nb thin film structure. We found that by co-annealing Nb films with Fe in Argon gas at above 400 $$^{\circ }$$ ∘ C for an hour, one can induce a Kondo effect in Nb. The Kondo effect is more pronounced at higher annealing temperature. The temperature dependence of the resistance suggests existence of remnant superconductivity at low temperatures even though the system never becomes superconducting. We find that the Hamann theory for the Kondo resistivity gives a satisfactory fitting to the result. The Hamann analysis gives a Kondo temperature for this Nb–Fe system at $$\sim $$ ∼ 16 K, well above the superconducting transition onset temperature 9 K of the starting Nb film, suggesting that the screening of the impurity spins is effective to allow Cooper pairs to form at low temperatures. We suggest that the mechanism by which the Fe impurities retain partially their magnetic moment is that they are located at the grain boundaries, not fully dissolved into the bcc lattice of Nb.

High-quality epitaxial LaCoO3 (LCO) thin films have been deposited on SrTiO3 (STO) substrates with pulsed laser deposition (PLD). We find that the LCO films undergo a typical ferromagnetic–paramagnetic (FM–PM) phase transition at ∼80 K. To understand the nature of magnetic phase transition, various methods, including the modified Arrott plot and critical isotherm analysis, were used to determine the critical exponents, which are β = 0.754(1) with a Curie temperature TC = 79.8(8) K and γ = 1.52(2) with TC = 79.9(2) K. The reliability of these critical exponents was confirmed using the Widom scaling relation and the scaling hypothesis. Further analysis revealed that the spin coupling within the LCO films exhibits two-dimensional (2D) long-range magnetic interaction and the magnetic exchange distance decays as J(r) ∼ r−(3.46). Our critical behavior analysis may shed new light on the further understanding of the origin of FM and the relatively fixed TC in LCO thin films.

For achieving more functionalities of perovskite manganese oxides film, an epitaxial La0.8Sr0.2MnO3 (LSMO) film was deposited on a flexible substrate (mica) by pulsed laser deposition. The film shows a paramagnetic-ferromagnetic (PM-FM) phase transition at 134 K together with metal-insulator transition (MIT) at 149 K. The measurement of hysteresis loop indicates that the easy-magnetization axis lied in film plane. The transport behavior can be fitted well with the small polaron model, giving out the activation energy Ehop = 176.9 meV. Different from the common anisotropic magnetoresistance (AMR) in manganite film, an isotropic magnetoresistance (IMR) effect was observed in LSMO film and the relatively small thickness of LSMO film ( ∼ 50 nm) is a major reason for it. After the cyclic flexural bending for 1.0 × 104 times, we found the magnetic properties of LSMO film were improved. Micromagnetic detection shows that the activation energy for polaron hopping (Ea = 144.7 meV) remarkably decreases by the cyclic flexural bending process. We suggested that the inhomogeneous/incompact part located at the zone of neighbouring domains become uniform and tight after circulating bending, which facilitates the rotation of domains and the polarons hopping so that the magnetic and electronic performance are enhanced.

The composition dependent magnetic structure in epitaxial BaFe12-xScxO19 (0 ≤ x ≤ 2.1, BaScM) thin films have been investigated. Results show that with increasing Sc3+ content, the out-of-plane c-axis lattice constants of BaScM films increase but do not follow the Vegard's law. The changes in hysteresis loops indicate a variation of magneto-crystalline anisotropy from the uniaxial-type for BaFe12O19 to the near-planar type for BaFe10.2Sc1.8O19. The remanent magnetic domains change from a mixture of dots and maze-like structure to more maze-like structure as the Sc3+ content increases. The above magnetic results can be explained by a composition dependent magnetic structure transition from collinear-type ferrimagnetic magnetic structure to the non-collinear conical magnetic structure which appears at Sc3+ content x ≥ 0.6. The ZFC/FC curves further show that the conical magnetic structure transition temperature (Tcone) of the films increases with the Sc3+ content until x ≥ 2.1. The above results may help better apply BaScM films in the electromagnetic devices.

Perovskite oxide SrVO3 (SVO) is a transparent conductor with excellent optical and electrical properties. Most of the previous works have focused on (001)-oriented SVO thin films. As an alternative to tin-doped indium oxide (ITO), the other orientations of SVO thin films are important to be considered as well. In the present work, the optical and electrical properties of (111)-oriented SVO epitaxial films have been investigated. Excellent electrical conductivity (2.92 × 104 S cm−1) and optical transparency (56.6%) have been demonstrated, which are comparable to those of ITO and expand the applications of epitaxial SVO thin films in other orientations as transparent conducting oxide.

The structural, Hall effect, electronic transport, and magnetic properties of Ge0.96−xBixFe0.04Te epitaxial thin film as prepared by pulsed laser deposition technique were reported. X-ray diffraction patterns including linear scans and phi scans confirmed that all films are high quality epitaxy and crystallinity. With the substitution of high valence Bi for Ge element, we found that the previous carriers of hole were changed to electron, which was testified by the negative slopes obtained from the measurements of Hall effect under different temperatures. The electronic transports show a typical semiconductor behavior and can be understood by the small polaron hopping model because the lattice distortions increase the electron-phonon interaction. An obvious ferromagnetic properties occur in the high Bi-doping Ge0.64Bi0.32Fe0.04Te rather than in that with low Bi-doping concentration, indicating that the ferromagnetic establishment is entirely dependent on carrier’s transmissions. The first-principles calculation performed on this system also reveals that the ferromagnetic state exactly exists in the present n-type diluted magnetic semiconductors with Bi co-dopants.

Self-assembly of non-spherical building blocks offers a potential route to photonic crystal supraparticles (PCSs) with novel structures and optical properties. However, experimental fabrications of anisotropic-particle-based PCSs have rarely been demonstrated owing to the requirement of additional control over the particle orientation during the assembly process. Here, we develop a spatially confined magnetic assembly strategy for the tailored assembly of ellipsoidal particles into PCSs with unusual non-close-packed structures. Detailed studies reveal that the transition of these metastable structures into close-packed structures is kinetically inhibited during the drying process owing to the synergy of spatial confinement and magnetic alignment. Unlike conventional PCSs, the nanoellipsoid-based PCSs exhibit anisotropic optical properties and multiple magneto-optical responses. The present work not only provides a model system for studying colloidal assembly under spatially confined conditions but also greatly extends the family of PCSs with interesting structures and properties, bringing new opportunities for applications in various areas.

We report an experimental study of the edge surface superconductivity and the Hall effect in a Nb thin film Hall device. We show that the previously reported anomalous sign reversal of the Hall resistance across the superconducting-normal transition is due to the edge supercurrent. Large anomalous oscillations between the transverse voltage probes are observed in the field range between Hc2 and Hc3, in both the anti-symmetric (Hall) and symmetric (resistive) channels. These oscillations are extremely sensitive to a small tilting of the edge surface relative to the external magnetic field. We suggest that these oscillations may arise from the Aharonov-Bohm interference of the edge supercurrents.

High-quality epitaxial LaCoO

Rare-earth monopnictides are predicted to be nontrivial semimetal candidates and show pressure-induced superconductivity. Here, we grow LuBi single crystal and study the magnetization, transport behaviors and electronic band structures to reveal its topological semimetal feature and superconductivity under pressure. At 0 GPa, the quantum oscillations indicate that there are several topologically nontrivial carrier pockets around the Fermi level, among which the hole ones are isotropic in shape, while the electron ones are anisotropic and responsible for the angular magnetoresistance. Upon compression, the superconductivity emerges in the titled compound, showing a similar pressure dependence as that observed in LaBi. Our calculation suggests that the electronic band structures are robust at low- and high-pressure respectively and thus the topological features are always preserved. Besides, the nearly pressure-independent density of state in LuBi indicates that the conventional electron-phonon coupling appears to play a minor role in the superconductivity.

We report spin–orbit torque (SOT) based on spin-torque ferromagnetic resonance (ST FMR) in a single ferrimagnetic layer. Temperature-dependent anomalous Hall resistance ([Formula: see text]) shows a magnetic compensation temperature ([Formula: see text]) of about 205 K. Temperature-dependent ST FMR is performed to quantify SOT; the torque is exerted to the total moment, and the SOT sign diverges as the temperautre approaches [Formula: see text]. X-ray photoelectron spectroscopy revealed that SOT arises due to the broken symmetry of the bulk spatial inversion along the normal direction of the film. Our finding provides useful information about the controlled temperature of bulk spin–orbit coupling in single layer GdFeCo.

Manufacture and characterizations of perovskite-mica van der Waals epitaxy heterostructures are a critical step to realize the application of flexible devices. However, the fabrication and investigation of the van der Waals epitaxy architectures grown on mica substrates are mainly limited to (111)-oriented perovskite functional oxide thin films up to now and buffer layers are highly needed. In this work, we directly grew La0.7Sr0.3MnO3 (LSMO) thin films on mica substrates without using any buffer layer. By the characterizations of x-ray diffractometer and scanning transmission electron microscopy, we demonstrate the epitaxial growth of the (110)-oriented LSMO thin film on the mica substrate. The LSMO thin film grown on the mica substrate via van der Waals epitaxy adopts domain matching epitaxy instead of conventional lattice matching epitaxy. Two kinds of domain matching relationships between the LSMO thin film and mica substrate are sketched by Visualization for Electronic and STructural Analysis software and discussed. A decent ferromagnetism retains in the (110)-oriented LSMO thin film. Our work demonstrates a new pathway to fabricate (110)-oriented functional oxide thin films on flexible mica substrates directly.

We re-visit the anomalous sign reversal problem in the Hall effect of the sputtered Nb thin films. We find that the anomalous sign reversal in the Hall effect is extremely sensitive to a small tilting of the magnetic field and to the magnitude of the applied current. Large anomalous variations are also observed in the symmetric part of the transverse resistance Rxy . We suggest that the surface current loops on superconducting grains at the edges of the superconducting thin films may be responsible for the Hall sign reversal and the accompanying anomalous effects in the symmetric part of Rxy .

We investigate the effect of carbon nanotubes (CNTs) on the crystalline microstructure and ferroelectric behavior of polyvinylidene fluoride- co-trifluoroethylene (P(VDF-TrFE)). X-ray analysis suggests that CNT can act as a template and direct the chain orientation of P(VDF-TrFE) crystals. In the presence of CNTs, the molecular chain axis ( c axis) of the β-phase crystal is oriented parallel to the long axis of CNTs. Moreover, we find that this templating effect did not cause a polymorph transition. For P(VDF-TrFE)/CNT composites, the crystallinity of P(VDF-TrFE) is slightly decreased. The orientation of the c axis induced by the templating effect of CNTs has a significant impact on the ferroelectric behavior of P(VDF-TrFE). As compared to a pure P(VDF-TrFE) film, the remnant polarization of the P(VDF-TrFE)/CNT composite is enhanced. Correspondingly, the piezoelectric property of the P(VDF-TrFE)/CNT composite shows a significant enhancement.

The magnetic properties of conical magnetic structure (CMS) hexaferrites BaFe10.2Sc1.8O19 (BFSO) and SrFe10.2Sc1.8O19 (SFSO) have been investigated under different magnetic fields and different temperatures. Results show that the single phase CMS hexaferrites BFSO and SFSO can be obtained as the sintering temperature exceeds 1473 K. Both the coercivity Hc and remanent magnetization Mr of the CMS BFSO and SFSO decrease sharply with increasing temperature below 100 K, and they become very small and almost invariant when the temperature exceeds 100 K. For both BFSO and SFSO, the field-cooling and zero-field-cooling curves differ greatly at low temperatures and resemble at high temperatures. A magnetic transition temperature Tz2 from noncollinear CMS to collinear ferrimagnetic structure is observed in both BFSO and SFSO with BFSO having higher Tz2 than that of SFSO. Moreover, the Tz2 decreases with increasing the magnetic field in both samples generally.

Site-selective growth on non-spherical seeds provides an indispensable route to hierarchical complex nanostructures that are interesting for diverse applications. However, this has only been achieved through epitaxial growth, which is restricted to crystalline materials with similar crystal structures and physicochemical properties. A non-epitaxial growth strategy is reported for hierarchical nanostructures, where site-selective growth is controlled by the curvature of non-spherical seeds. This strategy is effective for site-selective growth of silica nanorods from non-spherical seeds of different shapes and materials, such as α-Fe2 O3 , NaYF4 , and ZnO. This growth strategy is not limited by the stringent requirements of epitaxy and is thus a versatile general method suitable for the preparation of hierarchical nanostructures with controlled morphologies and compositions to open up a verity of applications in self-assembly, nanorobotics, catalysis, electronics, and biotechnology.

There has been growing interest in the preparation of anisotropic magnetic nanoparticles with well-controlled shapes and excellent colloidal dispersity. Here we report a general and mild approach for the preparation of highly dispersible anisotropic magnetic colloids through the low-temperature conversion of nonmagnetic templates. The key of our strategy is to modify the template surface with a layer of porous silica to provide a spatially confined environment necessary for the preservation of the overall morphology and improve the shell permeability necessary for the conversion at lower temperatures. The conversion under milder conditions not only is of practical importance for improving energy and cost-effectiveness but also produces magnetic particles with excellent colloidal dispersity by alleviating aggregation. We demonstrate the universality of this approach in the porous-silica-protected conversion of different samples including α-Fe2O3 and FeOOH into anisotropic magnetic particles with excellent colloidal dispersity. Based on highly dispersible anisotropic magnetic particles, we also demonstrate the fabrication of responsive photonic crystals for detecting very weak magnetic fields that are one order of magnitude higher than the earth magnetic field. Our study paves the way for new applications of anisotropic magnetic nanoparticles in self-assembly, catalysis, photonic crystals, liquid crystals, biomedicine and pharmaceutics.

The Rashba-Edelstein effect typically originates from inversion symmetry breaking at an interface that allows charge to spin conversion efficiency comparable to or larger than the SHE. Its potential value is in converting charge current into spin current. Here, we demonstrate experimentally an efficient charge to spin conversion at a Cu/Ta Rashba interface. We exploit spin-torque ferromagnetic resonance to detect a spin current from Cu/Ta interface into adjacent FeNi magnetic layer. The Ta thickness dependence of charge to spin conversion efficiency unambiguously ascribed that interface effect caused FeNi magnetization to precess by generating nonzero spin current that exerts torques rather than bulk effect. The possibility of controllable charge-spin conversion efficiency at room temperature opens another route for modulating the charge to spin conversion by interface engineering.

An experimental investigation of oblique sputtering angle on the magnetic compensation temperature (TM) in ferrimagnetic GdFeCo alloys is reported. These alloys exhibit a decrease ~ 200 K in TM with an increase of oblique sputtering angle. The films were deposited by magnetron sputtering from an alloyed target. The saturation magnetization (Ms) increased with oblique sputtering angle, but the concentration of Gd (at%) was unchanged. An ‘umbrella’-type magnetic structure is employed to explain the phenomenon of modulation of TM and Ms by oblique sputtering. Ferromagnetic resonance spectrometer measurements revealed a decrease in effective perpendicular magnetic anisotropy and increase of the effective in-plane anisotropy field with increase of oblique sputtering angle. This finding provides an alternative way to modulate TM and promotes the application of ferrimagnetic alloys for future high-performance spintronic devices

Coupling at the interfaces between antiferromagnetic and ferromagnetic constituents is known to be responsible for the exchange-bias effect, where external stimulus like temperature, electric or magnetic fields are supposed to influence the associated phenomenology. In this paper, we prepare the polycrystalline Co 2 TiO 4 and investigate its temperature- and field-dependent magnetization, from which an unusual exchange-bias effect associated with magnetic reversals is extracted. At low temperature, a continuous crossover from negative to positive exchange-bias fields can be obtained with increment of the cooling magnetic field, showing a magnetically tunable effect. The bipolar switching of exchange-bias field in this compound depends on the relative orientation between Co 2+ and [Co 3+ Ti 3+ ] magnetic moments.

The phase formation and magnetic property evolution processes of the hexaferrite with composition BaO⋅0.9Sc2O3⋅5.1Fe2O3 have been investigated. Results show that when the calcination temperature is lower than 1000 °C, the spinel phase BaFe2O4 and M-type hexaferrite phase BaFe12O19 dominate. The M-type hexaferrite BaFe12−xScxO19 (0

The magnetic properties of Sr 3-x Ba x Co 2 Fe 24 O 41 (0 ≤ x ≤ 3) Z-type hexaferrite powders have been investigated from 5 to 390 K. Results show that the lattice parameters ( a and c ) of the hexaferrite change with the Ba 2+ /Sr 2+ ratio but don't follow the Vegard's law. The magnetization reversal process changes from three-stage reversal process to two-stage reversal process as the Ba 2+ /Sr 2+ ratio increases. The above composition dependent magnetization reversal process of Sr 3-x Ba x Co 2 Fe 24 O 41 can be explained with the composition dependent conical magnetic structure model. The saturation magnetization of Sr 3-x Ba x Co 2 Fe 24 O 41 decreases only slightly with increasing the Ba content, but rapidly with increasing temperature. The coercivity (H c ) decreases with increasing temperature generally. Increasing Ba 2+ /Sr 2+ ratio leads to an increase in H c firstly and then H c decreases again at temperatures below 250 K. An increase in temperature does not lead to enormous changes of the magnetization in the field cooling curves below 390 K, but leads to a successive increase of the magnetization in the zero field cooling curves generally.

We report the gram-scale hydrothermal synthesis of superparamagnetic Fe3O4 CNCs with superior long-term charge stability, which are suitable building blocks for magnetically responsive photonic crystals (MRPCs) with widely, rapidly and reversibly tunable diffractions across the visible and near IR range, as well as long-term stability of photonic performances. The scalable synthesis of Fe3O4 CNCs with excellent long-term colloidal stability will facilitate their wide application in photonics, biomedicine, catalysis and other areas.