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Engineering magnetic anisotropy in a ferro- or ferrimagnetic (FM) thin film is crucial in spintronic device. One way to modify the magnetic anisotropy is through the surface of the FM thin film. Here, we report the emergence of a perpendicular magnetic anisotropy (PMA) induced by interfacial interactions in a heterostructure comprised of a garnet ferrimagnet, Y3Fe5O12 (YIG), and the low-symmetry, high spin orbit coupling (SOC) transition metal dichalcogenide, WTe2. At the same time, we also observed an enhancement in Gilbert damping in the WTe2 covered YIG area. Both the magnitude of interface-induced PMA and the Gilbert damping enhancement have no observable WTe2 thickness dependence down to single quadruple-layer, indicating that the interfacial interaction plays a critical role. The ability of WTe2 to enhance the PMA in FM thin film, combined with its previously reported capability to generate out-of-plane damping like spin torque, makes it desirable for magnetic memory applications., Nano Letters, in press

We report the magnetic and electronic transport properties of Mn-doped LaTi

Fe nGeTe2 ( n = 3, 4, and 5) has recently attracted increasing attention due to its two-dimensional van der Waals characteristic and high temperature ferromagnetism, which makes promises for spintronic devices. A Fe(1) split site is an important structural characteristic of Fe5GeTe2, which makes it very different from other Fe nGeTe2 ( n = 3 and 4) systems. The local atomic disorder and short-range order can be induced by the split site. In this work, high-quality van der Waals ferromagnet Fe5GeTe2 single crystals were grown to study low-temperature transport properties. We found a resistivity upturn below 10 K. The temperature and magnetic field dependence of the resistivity are in good agreement with a combination of the theory of disorder-enhanced three-dimensional electron–electron and single-channel Kondo effect. The Kondo effect exists only at low magnetic fields [Formula: see text], while electron–electron interaction dominates the appearance for the low-temperature resistivity upturn. We believe that the enhanced three-dimensional electron–electron interaction in this system is induced by the local atomic structural disorder due to the split site of Fe(1). Our results indicate that the split site of Fe plays an important role for the exceptional transport properties.

Multifunctional hybrid nanoparticles (NPs, ∼100 nm) that combine magnetic Fe3O4 nanocrystals and fluorescent carbon dots (CDs) in porous carbon (C) were successfully synthesized using a one-pot solvothermal method by simply increasing the H2O2 concentration. The resultant Fe3O4@C-CDs hybrid NPs not only demonstrate excellent magnetic responsive properties (Ms = 32.5 emu g−1) and magnetic resonance imaging ability (r*2 = 674.4 mM−1 s−1) from the Fe3O4 nanocrystal core, but also exhibit intriguing photoluminescent (quantum yield ∼6.8%) properties including upconversion fluorescence and excellent photostability from the CDs produced in the porous carbon. The hybrid NPs can enter the intracellular region and illuminate mouse melanoma B16F10 cells under different excitation wavelengths. Meanwhile, the mesoporous carbon shell and hydrophilic surface functional groups endow the hybrid NPs with high loading capacity (835 mg g−1) for the anti-cancer drug doxorubicin and excellent stability in aqueous solutions. More importantly, the hybrid NPs can absorb and convert near-infrared (NIR) light to heat due to the existence of CDs, and thus, can realise NIR-controlled drug release and combined photothermo/chemotherapy for high therapeutic efficacy. Such nanostructured Fe3O4@C-CDs hybrid NPs demonstrate great promise towards advanced nanoplatforms for simultaneous imaging diagnostics and high efficacy therapy.

A class of multifunctional hybrid nanoparticles (NPs) that can integrate a magnetic core, silver (Ag) nanocrystals, and a biocompatible poly(ethylene glycol) (PEG) shell were synthesized and characterized and their applications as antibacterial agents, optical labels for cellular imaging and drug carriers were tested. The synthetic strategy involves a one-step solvothermal synthesis of Fe

An investigation of the structural, magnetic, thermodynamic, and charge transport properties of non-centrosymmetric hexagonal ScFeGe reveals it to be an anisotropic metal with a transition to a weak itinerant incommensurate helimagnetic state below $T_N = 36$ K. Neutron diffraction measurements discovered a temperature and field independent helical wavevector \textbf{\textit{k}} = (0 0 0.193) with magnetic moments of 0.53 $\mu_{B}$ per formula unit confined to the {\it ab}-plane. Density functional theory calculations are consistent with these measurements and find several bands that cross the Fermi level along the {\it c}-axis with a nearly degenerate set of flat bands just above the Fermi energy. The anisotropy found in the electrical transport is reflected in the calculated Fermi surface, which consists of several warped flat sheets along the $c$-axis with two regions of significant nesting, one of which has a wavevector that closely matches that found in the neutron diffraction. The electronic structure calculations, along with a strong anomaly in the {\it c}-axis conductivity at $T_N$, signal a Fermi surface driven magnetic transition, similar to that found in spin density wave materials. Magnetic fields applied in the {\it ab}-plane result in a metamagnetic transition with a threshold field of $\approx$ 6.7 T along with a sharp, strongly temperature dependent, discontinuity and a change in sign of the magnetoresistance for in-plane currents. Thus, ScFeGe is an ideal system to investigate the effect of in-plane magnetic fields on an easy-plane magnetic system, where the relative strength of the magnetic interactions and anisotropies determine the topology and magnetic structure., Comment: 15 pages, 13 figures

Binary Cr-Te compounds are known to exhibit various structures and interesting physical properties, which are very sensitive to Cr content and arrangement. We report the structure and physical properties of a compound $\mathrm{C}{\mathrm{r}}_{12\ensuremath{-}x}\mathrm{T}{\mathrm{e}}_{16}$ with $x\ensuremath{\sim}2.65$. $\mathrm{C}{\mathrm{r}}_{9.35}\mathrm{T}{\mathrm{e}}_{16}$ crystallizes in the trigonal structure with the space group $P\overline{3}m1$ (No. 164), consisting of four different Cr sites (Cr1, Cr2, Cr3, Cr4) with an ordered Cr4 vacant layer. The electrical resistivity, magnetization, specific heat, and neutron diffraction measurements indicate that there is a ferromagnetic transition at ${T}_{\mathrm{C}1}\ensuremath{\sim}160$ K with the first-order nature, and an anomaly at ${T}_{\mathrm{C}2}\ensuremath{\sim}67$ K. At 5 K, the magnetic moments of Cr2 and Cr3 are aligned along the $c$ axis with $2.78\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Cr}$. Detailed neutron diffraction refinement suggests that ordered magnetic moments on Cr1 (fully occupied) and Cr4 (partially occupied) are negligible. The different magnetic response stems from different valence states and different magnetic interactions between Cr2/Cr3 and Cr1/Cr4 as evidenced by the x-ray absorption fine-structure measurements. This creates a unique two-dimensional magnetic system with ordered moments confined in the Cr2/Cr3 layer.

Interface plays a critical role in determining the physical properties and device performance of heterostructures. Traditionally, lattice mismatch, resulting from the different lattice constants of the heterostructure, can induce epitaxial strain. Over past decades, strain engineering has been demonstrated as a useful strategy to manipulate the functionalities of the interface. However, mismatch of crystal symmetry at the interface is relatively less studied due to the difficulty of atomically structural characterization, particularly for the epitaxy of low symmetry correlated materials on the high symmetry substrates. Overlooking those phenomena restrict the understanding of the intrinsic properties of the as- determined heterostructure, resulting in some long-standing debates including the origin of magnetic and ferroelectric dead layers. Here, perovskite LaCoO3-SrTiO3 superlattice (SL) is used as a model system to show that the crystal symmetry effect can be isolated by the existing interface strain. Combining the state-of-art diffraction and electron microscopy, it is found that the symmetry mismatch of LaCoO3-SrTiO3 SL can be tuned by manipulating the SrTiO3 layer thickness to artificially control the magnetic properties. The work suggests that crystal symmetry mismatch can also be designed and engineered to act as an effective strategy to generate functional properties of perovskite oxides.

We report the synthesis of single-crystal iron germanium nanowires via chemical vapor deposition without the assistance of any catalysts. The assembly of single-crystal FeGe2 nanowires with tetragonal C16 crystal structure shows anisotropic magnetic behavior along the radial direction or the growth axial direction, with both antiferromagnetic and ferromagnetic orders. Single FeGe2 nanowire devices were fabricated using e-beam lithography. Electronic transport measurement in these devices show two resistivity anomalies near 250 K and 200 K which are likely signatures of the two spin density wave states in FeGe2.

We study proximity-induced spin-orbit coupling (SOC) in bilayer graphene/few-layer WSe2 heterostructure devices. Contact mode atomic force microscopy (AFM) cleaning yields ultra-clean interfaces and high-mobility devices. In a perpendicular magnetic field, we measure the quantum Hall effect to determine the Landau level structure in the presence of out-of-plane Ising and in-plane Rashba SOC. A distinct Landau level crossing pattern emerges when tuning the charge density and displacement field independently with dual gates, originating from a layer-selective SOC proximity effect. Analyzing the Landau level crossings and measured inter-Landau level energy gaps yields the proximity induced SOC energy scale. The Ising SOC is ~ 2.2 meV, 100 times higher than the intrinsic SOC in graphene, while its sign is consistent with theories predicting a dependence of SOC on interlayer twist angle. The Rashba SOC is ~15 meV. Finally, we infer the magnetic field dependence of the inter-Landau level Coulomb interactions. These ultraclean bilayer graphene/WSe2 heterostructures provide a high mobility system with the potential to realize novel topological electronic states and manipulate spins in nanostructures., Nano Letters, in press

We study proximity-induced spin-orbit coupling (SOC) in bilayer graphene/few-layer WSe

The dimensionality of the electronic and magnetic structure of a given material is generally predetermined by its crystal structure. Here, using elastic and inelastic neutron scattering combined with magnetization measurements, we find unusual magnetic behavior in three-dimensional (3D) ${\mathrm{Ba}}_{2}{\mathrm{CoO}}_{4}$. In spite of isolated ${\mathrm{CoO}}_{4}$ tetrahedra, the system exhibits a 3D noncollinear antiferromagnetic order in the ground state with an anomalously large Curie-Weiss temperature of 110 K compared to ${T}_{\mathrm{N}}=26$ K. More unexpectedly, spin dynamics displays quasi-two-dimensional spin-wave dispersion with an unusually large spin gap, and one-dimensional magnetoelastic coupling. Our results indicate that ${\mathrm{Ba}}_{2}{\mathrm{CoO}}_{4}$ is a unique system for exploring the interplay between isolated polyhedra, low-dimensional magnetism, and spin states in oxides.

Rational control of local strain distributions and thus the functional properties of epitaxial thin films has been a long-standing goal in the development of new physics and novel devices based on strain-sensitive materials. Here, the fabrication of La2/3Sr1/3MnO3 (LSMO) films with strain fields arising from vertical epitaxial embedding of ultra-small ZrO2 nanopillars, diameter 4.0 +/- 0.6 nm, is reported. High quality films are obtained with average distance between adjacent nanopillars of 9.0 +/- 0.3 nm for x = 0.2 in (LSMO)(1-)(x):(ZrO2)(x). The strain distribution of the vertical interface is analyzed in detail and the dominant state of the interfacial strain is verified. Remarkably, with increasing x, the Curie temperature T-C and metal-insulator (MI) transition temperature T-MI show a surprisingly large depression, revealing the significant tuning capability of the vertical tensile stress originating from the small-size ZrO2 pillars. A systematic tunability of the low field magnetoresistance is also found. The field dependence of the magnetization exhibits both horizontal and vertical shifts. The exchange bias field H-E increases with increasing x, while magnetization shift M-shift is unchanged. The results suggest the possibility of strain tuning through epitaxial nanostructures for multifunctional applications across many fields with appropriate selection of matrix and nanopillar materials.

Magnetic nanoparticles are of great technological interest because they promise numerous potential opportunities in biomedicine and data storage. Although intriguing, these applications require exquisite control over nanostructure morphology in order to appropriately harness their magnetic properties. Most synthesis strategies reported to date are unable to routinely produce anisotropic Fe3O4 nanostructures with appropriate sizes to enable integration into biological systems. Here, we report a simple solvothermal synthesis for obtaining octahedral Fe3O4 nanoparticles with suitable sizes for cellular internalization. Furthermore, these ferromagnetic Fe3O4 octahedrons exhibit substantial saturation magnetization with minimal remanence, suggesting their potential applicability for a host of biomedical applications.

We report experimental investigations of the electrical transport, magnetic, and thermodynamic properties of $\mathrm{IrT}{\mathrm{e}}_{2}$ single crystals. The resistivity, magnetization, and specific heat display anomalies at ${T}_{\mathrm{S}1}\ensuremath{\approx}283\phantom{\rule{0.16em}{0ex}}\mathrm{K},{T}_{\mathrm{S}2}\ensuremath{\approx}167\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and ${T}_{\mathrm{c}}\ensuremath{\approx}2.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, corresponding to two structural and one superconducting phase transitions, respectively, demonstrating the coexistence of all of these transitions in high-quality stoichiometric samples. While there is little magnetic anisotropy, a large $ab$-plane $({\ensuremath{\rho}}_{\mathrm{ab}})$ and $c$-axis $({\ensuremath{\rho}}_{\mathrm{c}})$ electrical resistivity ratio $({\ensuremath{\rho}}_{\mathrm{c}}/{\ensuremath{\rho}}_{\mathrm{ab}}\ensuremath{\approx}730$ at $T=4\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ is observed. This two-dimensional (2D) electronic character is further reflected in the disparate temperature dependences of ${\ensuremath{\rho}}_{\mathrm{ab}}$ and ${\ensuremath{\rho}}_{\mathrm{c}}$, with ${\ensuremath{\rho}}_{\mathrm{ab}}$ exhibiting a Fermi-liquid-like ${T}^{2}$ dependence below $\ensuremath{\sim}25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, while ${\ensuremath{\rho}}_{\mathrm{c}}$ deviates significantly from this standard metallic behavior. In contrast, the magnetization is almost isotropic and negative over a wide temperature range. This can be explained by larger diamagnetism induced by electronic structure reconstruction as probed by the Hall effect and smaller positive contribution from itinerant electrons due to a low density of states (DOS) at the Fermi level. A small electronic specific heat coefficient with $\ensuremath{\gamma}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}1.8\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/\mathrm{mol}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{2}$ confirms this assertion. This implies that $\mathrm{IrT}{\mathrm{e}}_{2}$ is a weakly coupled superconductor. The connection between the superconductivity and the two structural transitions is discussed.

MnSi in the B20 structure is a prototypical helimagnet that forms a skyrmion lattice, a vortex-like spin texture under applied magnetic field. We have systematically explored the synthesis of single crystal MnSi nanowires via controlled oxide-assisted chemical vapor deposition and observed a characteristic signature of skyrmion magnetic ordering in the MnSi nanowires. The thickness of the SiO2 layer on the Si substrate plays the key role in obtaining a high yield of B20 MnSi skyrmion nanowires. A growth mechanism was proposed that is consistent with the existence of an optimum SiO2 thickness. A growth phase diagram was constructed based on the extensive studies of various growth conditions for various MnSi nanostructures. The persistence of both the helicoidal and skyrmion magnetic ordering in the one-dimensional wires was directly revealed by ac and dc magnetic measurements.

While the assembled 1D magnetic nanoparticle (NP) chains have demonstrated synergistic magnetic effects from the individual NPs, it is essential to prepare new 1D NP chains that can combine the magnetism with other important material properties for multifunctional applications. This paper reports the fabrication and multifunctional investigation of a new type of 1D NP chains that combine the magnetic properties with fluorescent properties, photothermal conversion ability, and drug carrier function. The building block NPs are composed of magnetic Fe(3)O(4) nanocrystals clustered in the core and fluorescent carbon dots embedded in the mesoporous carbon shell with hydroxyl/carboxyl groups anchored on their surface. These NPs can assemble under the induction of external magnetic field and form stable 1D NP chains of diameter ∼ 90 nm and length ∼ 3 μm via the hydrogen bonding and π-π stacking linkage of the carbon shell. The resulted 1D hybrid NP chains not only demonstrate much higher magnetic resonance imaging (MRI) contrasting ability than the dispersed building block NPs, but also enter into intracellular region and light up the B16F10 cells under a laser excitation with strong and stable fluorescence. While the mesoporous carbon shell provides high drug loading capacity, the embedded fluorescent carbon dots convert near-infrared (NIR) light to heat, and hence kill the tumor cells efficiently and enhance the drug release rate to further improve the therapeutic efficacy under NIR irradiation. Such designed 1D magnetic-fluorescent hybrid NP chains with enhanced MRI contrast, fluorescent imaging ability, and combined chemo-/photothermal therapeutic ability have great potential for various biomedical applications.

The dispersive magnetic excitations in ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ have previously been well described within an isospin-1/2 Heisenberg model on a square lattice that revealed parallels with ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$. Here we investigate the inelastic spectra of ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{0.8}{\mathrm{Ru}}_{0.2}{\mathrm{O}}_{4}$ with resonant inelastic x-ray scattering (RIXS) at the Ir ${L}_{3}$ edge. The results are well described using linear spin-wave theory within a similar Heisenberg model applicable to ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$; however, the disorder induced by the substitution of $20%\phantom{\rule{4pt}{0ex}}{\mathrm{Ir}}^{4+}$ ions for ${\mathrm{Ru}}^{4+}$ removes longer range exchange interactions. A large spin gap (40 meV) is measured indicating strong anisotropy from spin-orbit coupling that is manifest due to the altered magnetic structure in ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{0.8}{\mathrm{Ru}}_{0.2}{\mathrm{O}}_{4}$ with $c$-axis aligned moments compared to the basal plane moments in the parent. Collectively the results indicate the robustness of a Heisenberg model description even when the magnetic structure is altered and the ${J}_{\mathrm{eff}}=1/2$ moments are diluted.

A simple and facile synthetic strategy is developed to prepare a new class of multifunctional hybrid nanoparticles (NPs) that can integrate a magnetic core with silver nanocrystals embedded in porous carbon shell. The method involves a one-step solvothermal synthesis of Fe3O4@C template NPs with Fe3O4nanocrystals in the core protected by a porous carbon shell, followed by loading and in situ reduction of silver ions in the carbon shell in water at room temperature. The core-satellite and dumbbell-like nanostructures of the resulted Fe3O4@C-Ag hybrid NPs can be readily controlled by loading amount of silver ions. The hybrid NPs can efficiently catalyze the reduction reaction of organic dyes in water. The easy magnetic separation and high stability of the catalytically active silver nanocrystals embedded in the carbon shell enable the hybrid NPs to be recycled for reuse as catalysts. The hybrid NPs can also overcome cellular barriers to enter the intracellular region and light up the mouse melanoma B16F10 cells in multicolor modal, with no cytotoxicity. Such porous carbon protected Fe3O4@C-Ag hybrid NPs with controllable nanostructures and a combination of magnetic and noble metallic components have great potential for a broad range of applications in the catalytic industry and biomedical field.

We report the observation of anomalous magnetic anisotropy driven by nonmagnetic ZrO 2 nanoparticles in epitaxial La 2/3 Sr 1/3 MnO (LSMO) films grown on LaAlO 3 (LAO) substrates. The compressive epitaxial strain imposed by the lattice mismatch of substrate and film is tuned by the density of ZrO 2 nanoparticles embedded in the film matrix and affects the magnetic anisotropy as well as the magnetotransport properties. Epitaxial 54 nm thick LSMO thin films with different concentrations of ZrO 2 nanoparticles demonstrate anisotropic hysteresis loops concomitant with anisotropic magnetotresistance behavior. The biaxial epitaxial strain, induced by the substrate/film lattice parameter mismatch is partially relaxed by increasing the density of precipitates and they serve as a tuning parameter for the strain state. We interpret our results by a strain-induced interplay of impurity scattering, weak localization and magnetic domain structure.

We explore the low-temperature magnetotransport properties of La2/3Sr1/3MnO3 (LSMO) epitaxial films with nano-scaled non-magnetic ZrO2 precpitates and analyze the low-temperature resistance anomalies within the frame of precipitate-induced Quantum Interference Effects (QIE) and anisotropic magnetoresistance. Two competing mechanisms triggered by the ZrO2 nanoparticles, weak localization and magnetic domain pattern modifications, are proposed to govern the observed anomalous magnetic response at low and high magnetic fields, respectively. The occurrence of these anomalies in LSMO with non-magnetic ZrO2 clusters shines new light at defect-induced magnetoelastic coupling.

A special type of anisotropic spin exchange called the ``Kitaev interaction'' provides rare exactly-soluble models of gapless quantum spin liquids in 2d and 3d. The main goals of this work were to identify other lattice geometries that support the elusive Kitaev interactions and understand the magnetic properties of such materials. By performing inelastic neutron scattering on La${}_{2}$MgIrO${}_{6}$ and La${}_{2}$ZnIrO${}_{6}$, the authors find that these magnets, which possess long-range antiferromagnetic order, yield clear signatures of gapped and nearly-dispersionless magnon excitations. They also show that spin-wave models with a dominant Kitaev interaction can naturally account for the magnetic ordering pattern as well as the inelastic neutron scattering data.

We investigate the magnetic properties of the series ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{4}$ with neutron, resonant x-ray, and magnetization measurements. The results indicate an evolution and coexistence of magnetic structures via a spin-flop transition from $ab$-plane to $c$-axis collinear order as the $5d {\mathrm{Ir}}^{4+}$ ions are replaced with an increasing concentration of $4d {\mathrm{Ru}}^{4+}$ ions. The magnetic structures within the ordered regime of the phase diagram ($xl0.3$) are reported. Despite the changes in magnetic structure no alteration of the ${J}_{\mathrm{eff}}=1/2$ ground state is observed. The behavior of ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{4}$ is consistent with electronic phase separation and diverges from a standard scenario of hole doping. The role of lattice alterations with doping on the magnetic and insulating behavior is considered. The results presented here provide insight into the magnetic insulating states in strong spin-orbit coupled materials and the role perturbations play in altering the behavior.

Magnetic field induced step-like transport jump is found at low temperature for Pr doped phase-separated manganites. Magnetization measurements indicate that spin-stiffness constant D exhibits large magnetic field dependence. Moreover, there exists a remarkable change of spin-stiffness constant corresponding to the variety of the step-like transport jump. This suggests a possible existence of quantum orbital transfer resulting from the change of orbital ordering (OO) modes and accompanying with spin reorientation and carrier delocalization. The carrier delocalization is closely related to the coupling of charge–orbital and can be proved from the low temperature resistivity minimum behavior. The phase diagram was determined. These all show the importance of the strong interaction of charge–orbital and/or spin–orbital in the adjacent long-range charge-ordered antiferromagnetic phase, which depends sensitively on the OO modes.

This paper reports a type of multifunctional hybrid nanoparticle (NP) composed of gold nanocrystals coated on and/or embedded in a magnetite-fluorescent porous carbon core-shell NP template (Fe3O4@PC-CDs-Au) for biomedical applications, including magnetic/NIR-responsive drug release, multicolor cell imaging, and enhanced photothermal therapy. The synthesis of the Fe3O4@PC-CDs-Au NPs firstly involves the preparation of core-shell template NPs with magnetite nanocrystals clustered in the cores and fluorescent carbon dots (CDs) embedded in a porous carbon shell, followed by an in situ reduction of silver ions (Ag(+)) loaded in the porous carbon shell and a subsequent replacement of Ag NPs with Au NPs through a galvanic replacement reaction using HAuCl4 as a precursor. The Fe3O4@PC-CDs-Au NPs can enter the intracellular region and light up mouse melanoma B16F10 cells in multicolor mode. The porous carbon shell, anchored with hydrophilic hydroxyl/carboxyl groups, endows the Fe3O4@PC-CDs-Au NPs with excellent stability in the aqueous phase and a high loading capacity (719 mg g(-1)) for the anti-cancer drug doxorubicin (DOX). The superparamagnetic Fe3O4@PC-CDs-Au NPs with a saturation magnetization of 23.26 emu g(-1) produce localized heat under an alternating magnetic field, which triggers the release of the loaded drug. The combined photothermal effects of the Au nanocrystals and the CDs on/in the carbon shell can not only regulate the release rate of the loaded drug, but also efficiently kill tumor cells under NIR irradiation. Benefitting from their excellent optical properties, their magnetic field and NIR light-responsive drug release capabilities and their enhanced photothermal effect, such nanostructured Fe3O4@PC-CDs-Au hybrid NPs are very promising for simultaneous imaging diagnostics and high efficacy therapy.

The epitaxially stabilized metallic α-FeSi2 thin films on Si(001) were grown using pulsed laser deposition. While the bulk material of α-FeSi2 is a high temperature metastable phase and nonmagnetic, the thin film is stabilized at room temperature and shows unusual electronic transport and magnetic properties due to strain modification. The transport renders two different conducting states with a strong crossover at 50 K accompanied by an onset of ferromagnetism as well as a substantial magnetocaloric effect and magnetoresistance. These experimental results are discussed in terms of the unusual electronic structure of α-FeSi2 obtained within density functional calculations and Boltzmann transport calculations with and without strain. Our findings provide an example of a tailored material with interesting physics properties for practical applications.

The magnetic and transport properties of Pr0.5Ca0.5MnO3 with a CE-type antiferromagnetic structure were systematically investigated. A distinctive sequence of multiple magnetic transitions is found: paramagnetic (PM)–ferromagnetic (FM)–antiferromagnetic (AFM)–spin glass (SG) transitions. The results show that the low-temperature SG state is different from a conventional SG but has a reentrant character. The reentrant SG behavior accompanied with colossal magnetoresistance might be due to the competing interaction between FM and the CE-type AFM matrix. Also, this phase may be related to the disorder due to the variance of tolerance factor t and characteristic parameter σ 2 (reflecting A-site cation size variance). Meanwhile, this kind of reentrant SG state exists in most manganites and it shows a complex magnetic ground state. The present experimental data establishes that Pr0.5Ca0.5MnO3 compound shows the coexistence of FM clusters and SG clusters in the background of an AFM matrix. Here, all the rich variety of phases can be explained by the bandgap modified locally by strain within each grain. At the same time, the present results indicate also that Pr0.5Ca0.5MnO3 has a ground state, which shows the presence of some FM clusters in the background of the remaining region in a spin frozen state. The RSG phenomena should be a universal characteristic of manganites with CE-type AFM structure and it is very sensitive to the subtle disorder.

The multi-step transition by the field inducement is reported in pristine Pr 2/3 Ca 1/3- MnO 3 manganites. This step effect shows a strong dependence on the temperature and field sweep rate, which is sensitive to thermal perturbation. The results prove that they are related with the internal magnetic structure of phase-separated Pr 2/3 Ca 1/3 MnO 3 manganites in low temperatures, while the influence of sweep rate can be accounted for within a martensitic-like scenario.

The lattice effect and magnetic transition behaviors of (Pr 1− y Nd y ) 0.67 Sr 0.33 MnO 3 ( y =0, 1/4, 2/4, 3/4, 1) samples under superposed magnetic fields (i.e. the superposed AC and DC magnetic field) were systematically studied in the temperature range from 4.2 to 330 K. The results show that the magnetic transition temperature (Curie temperature, T C ) of (Pr 1− y Nd y ) 0.67 Sr 0.33 MnO 3 shifts to a lower temperature as Nd substitutes for Pr, which is related to the degree of lattice distortion. The magnetization of samples increases with the increase in applied magnetic field and the in-phase-part of the AC susceptibility decreases as the superposed DC magnetic field increases. Under superposed magnetic fields, a characteristic sharp peak of the in-phase part of the susceptibility appears near T C . For the (Pr 1− y Nd y ) 2/3 Sr 1/3 MnO 3 system, as the Nd content increases, the peak temperature of the relative variation for the in-phase part of magnetic susceptibility ( Eχ ′=Δ χ ′/ χ ′ dc ) decreases, in consistent with that of the magnetoresistivity of this system. The magnetic transition behaviors under superposed magnetic fields for the manganite systems are discussed.

To recognize the distributional characteristics of Fe and Ni doping and the fundamental effects of magnetic ions on superconductivity, the X-ray diffraction, positron annihilation technology and simulated calculations are utilized to investigate systemically YBa 2 Cu 3-x( Fe , Ni )x O 7-δ(x=0.0~0.5). The results show that Fe and Ni doping form different kinds of ion clusters and enter the crystal lattice. When occupying Cu (2) sites in the CuO 2 planes, ions gather into Double Square and/or other clusters, which results in a strong electronic localization and would directly influence the pairing and transportation of carriers, so the superconductivity is suppressed dramatically. While doping ions enter the Cu (1) sites through gathering Hexamer and/or other clusters, this induces the localization of holes and weakens the function of carrier reservoir, so carriers cannot be easily transferred to the CuO 2 planes. However, in this case, the pairing and transportation of carriers are not affected directly, thus the superconductivity is suppressed weakly. Besides, the present results indicate that the superconductivity suppressed has no direct correlation with the magnetism of Fe and Ni ion itself.

The Pr -substituted YBa 2 Cu 3 O 7-δ( Y 123) superconducting systems with the content of 0.0–1.0 have been systematically studied by positron lifetime and infrared absorption experiments. The results show that the short lifetime τ1 decreases as a function of Pr -substitution x below x=0.6, but when above x=0.6, it increases inversely. The long lifetime τ2 decreases as a function of Pr -substituted x. Based on the present results, we discuss that Pr 4+ substitutes on Ba 2+ ion and forms Pr Ba defects. The variation of τ1 is caused by the oxygen vacancies and τ2 is probably affected by the absence of Cu due to Pr Ba defects. The infrared absorption of Pr -substituted Y 123 systems gives three variational modes, located at 560 cm -1( A 1), 1435 cm -1( A 2) and 1631 cm -1( A 3) respectively. Here the A 3 mode shows that with Pr content increasing from x=0.1 to 1.0, the infrared absorption decreases and the peak tends to broaden. So, combining with the results of the positron lifetime spectra, we can argue that there always exists portion of Pr Ba defects in the Pr -substituted systems, and the Pr 4+ substituted into Ba 2+ is also increasing with the Pr content increasing. When the Pr content is 0.6, the systems have a metal-insulator transition and Pr Ba defects begin to domain the samples' microstructure.

Based on possible existence of technique effect and scattered distribution in positron results, a special investigation was made for YBa2Cu3O7 � d systems in this paper. The dependence of preparation techniques and the structural characteristics on the sintering temperature and time are also given by positron lifetime, XRD and SEM experiments. The results show that the positron lifetime parameters and the microstructure show a significant dependence on sintering temperature and time. It is proved that, in the range of 920–950 jC/12–72 h, the positron results have good stability and reliability in the sintering times and temperature. The distribution characteristic of defect was evaluated and had a good stability in the preparation technique. The present studies provide an important experimental evidence for the study of Y-123 systems by positron experiment. D 2002 Elsevier Science B.V. All rights reserved.

Pr-substituted YBCO system has been studied by positron lifetime experiment in the range from 0.0 to 1.0. The present results show that the value of short lifetime τ 1 in PrBa 2 Cu 3 O 7− δ is nearly the same as in the isostructural YBa 2 Cu 3 O 7− δ and the defect-related positron lifetime component τ 2 decreases as a function of Pr-substitution x . The increase of local electron density n e reflects the electronic intense localization. These experimental results are interpreted in terms of the localization of hole carriers in the Cu–O chains on Pr substitution due to disorder in the Ba and Pr planes by the partly occupation of Ba 2+ ion site with Pr 3+ ion. These will destroy the intrinsic conductivity of the Cu–O chains and so impresses the superconductivity above x =0.6 Pr-substitution concentration.

A metastable phase α-FeSi_{2} was epitaxially stabilized on a silicon substrate using pulsed laser deposition. Nonmetallic and ferromagnetic behaviors are tailored on α-FeSi_{2} (111) thin films, while the bulk material of α-FeSi_{2} is metallic and nonmagnetic. The transport property of the films renders two different conducting states with a strong crossover at 50 K, which is accompanied by the onset of a ferromagnetic transition as well as a substantial magnetoresistance. These experimental results are discussed in terms of the unusual electronic structure of α-FeSi_{2} obtained within density functional calculations and Boltzmann transport calculations with and without strain. Our finding sheds light on achieving ferromagnetic semiconductors through both their structure and doping tailoring, and provides an example of a tailored material with rich functionalities for both basic research and practical applications.

The ${J}_{\mathrm{eff}}=\frac{1}{2}$ state is manifested in systems with large cubic crystal field splitting and spin-orbit coupling that are comparable to the on-site Coulomb interaction, $U$. $5d$ transition-metal oxides host parameters in this regime and strong evidence for this state in ${\text{Sr}}_{2}$${\text{IrO}}_{4}$, and additional iridates, has been presented. All the candidates, however, deviate from the cubic crystal field required to provide an unmixed canonical ${J}_{\mathrm{eff}}=\frac{1}{2}$ state, impacting the development of a robust model of this novel insulating and magnetic state. We present experimental and theoretical results that not only show ${\text{Ca}}_{4}$${\text{IrO}}_{6}$ hosts the state, but furthermore uniquely resides in the limit required for a canonical unmixed ${J}_{\mathrm{eff}}=\frac{1}{2}$ state.

The oxygen stoichiometry has a large influence on the physical and chemical properties of complex oxides. Most of the functionality in e.g. catalysis and electrochemistry depends in particular on control of the oxygen stoichiometry. In order to understand the fundamental properties of intrinsic surfaces of oxygen-deficient complex oxides, we report on in situ temperature dependent scanning tunnelling spectroscopy experiments on pristine oxygen deficient, epitaxial manganite films. Although these films are insulating in subsequent ex situ in-plane electronic transport experiments at all temperatures, in situ scanning tunnelling spectroscopic data reveal that the surface of these films exhibits a metal-insulator transition (MIT) at 120 K, coincident with the onset of ferromagnetic ordering of small clusters in the bulk of the oxygen-deficient film. The surprising proximity of the surface MIT transition temperature of nonstoichiometric films with that of the fully oxygenated bulk suggests that the electronic properties in the surface region are not significantly affected by oxygen deficiency in the bulk. This carries important implications for the understanding and functional design of complex oxides and their interfaces with specific electronic properties for catalysis, oxide electronics and electrochemistry.