Microrobots and metal-organic frameworks (MOFs) have been identified as promising carriers for drug delivery applications. While clinical applications of microrobots are limited by their low drug loading efficiencies and the poor degradability of the materials used for their fabrication, MOFs lack motility and targeted drug delivery capabilities. The combination of these two fields marks the beginning of a new era; MOF-based small-scale robots (MOFBOTs) for biomedical applications. Yet, biodegradability is a major hurdle in the field of micro-and nanoswimmers including small-scale robots. Here, a highly integrated MOFBOT that is able to realize magnetic locomotion, drug delivery, and selective degradation in cell cultures is reported for the first time. The MOF used in the investigations does not only allow a superior loading of chemotherapeutic drugs and their controlled release via a pH-responsive degradation but it also enables the controlled locomotion of enzymatically biodegradable gelatin-based helical microrobots under magnetic fields. The degradation of the integrated MOFBOT is observed after two weeks, when all its components fully degrade. Additionally, drug delivery studies performed in cancer cell cultures show reduced viability upon delivery of Doxorubicin within short time frames. This MOFBOT system opens new avenues for highly integrated fully biodegradable small-scale robots.

Magneto-electric multiferroics exemplified by TbMnO 3 possess both magnetic and ferroelectric long-range order. The magnetic order is mostly understood, whereas the nature of the ferroelectricity has remained more elusive. Competing models proposed to explain the ferroelectricity are associated respectively with charge transfer and ionic displacements. Exploiting the magneto-electric coupling, we use an electric field to produce a single magnetic domain state, and a magnetic field to induce ionic displacements. Under these conditions, interference charge-magnetic X-ray scattering arises, encoding the amplitude and phase of the displacements. When combined with a theoretical analysis, our data allow us to resolve the ionic displacements at the femtoscale, and show that such displacements make a significant contribution to the zero-field ferroelectric moment.The discovery of spin-cycloid multiferroics, in which the onset of non-collinear magnetic order leads to a spontaneous ferroelectric polarization, has generated considerable interest in 1 arXiv:1110.2875v1 [cond-mat.str-el] 13 Oct 2011 the control of electric polarization by magnetic fields, and vice versa (1, 2). While comprehensive, microscopic descriptions of their magnetic structures have been obtained (3-11), our understanding of the ferroelectric state is still emerging. Two competing theoretical scenarios have been proposed: one purely electronic, without ionic displacements (12); one based on anti-symmetric exchange interactions, with ionic displacements (13). Experiments have been unable to resolve the individual ionic displacements (14).Spin-cycloid multiferroics exhibit an exceptionally strong cross-coupling between the different types of order, as demonstrated when the electric (magnetic) field E (H) was used to control magnetization M (ferroelectric polarization P) (1,5,(15)(16)(17)(18). Interest in this class of multiferroic has been generated both by the potential for novel devices, and the challenge they represent to our fundamental understanding of ordering phenomena in solids. TbMnO 3 is the prototypical spin-cycloid multiferroic (1). Diffraction studies have established that in its ferroelectric phase below ∼30 K the Mn magnetic moments form a cycloid in the bc plane (3), while the Tb moments order sinusoidally (5), Fig. 1A,B. Formation of the cycloid removes the centre of inversion at the Mn sites and generates a spontaneous P along c. The scenario in which P is generated by ionic displacements has been investigated by ab-initio density functional theory (DFT) (19,20) which makes definite predictions for the displacements of the constituent ions. Experimentally, only an upper limit (of ∼500 fm) has been estimated for the ionic displacements from EXAFS measurements (14); EXAFS has been used to obtain femtoscale displacements in other systems (21). Application of a sufficiently strong magnetic field along either the a or b axis results in the flopping of P from the c to a axis (6, 15). Conventional X-ray scattering in an applied magnetic fie...

Defects in ceramic materials are generally seen as detrimental to their functionality and applicability. Yet, in some complex oxides, defects present an opportunity to enhance some of their properties or even lead to the discovery of exciting physics, particularly in the presence of strong correlations. A paradigmatic case is the high‐temperature superconductor YBa2Cu3O7‐δ (Y123), in which nanoscale defects play an important role as they can immobilize quantized magnetic flux vortices. Here previously unforeseen point defects buried in Y123 thin films that lead to the formation of ferromagnetic clusters embedded within the superconductor are unveiled. Aberration‐corrected scanning transmission microscopy has been used for exploring, on a single unit‐cell level, the structure and chemistry resulting from these complex point defects, along with density functional theory calculations, for providing new insights about their nature including an unexpected defect‐driven ferromagnetism, and X‐ray magnetic circular dichroism for bearing evidence of Cu magnetic moments that align ferromagnetically even below the superconducting critical temperature to form a dilute system of magnetic clusters associated with the point defects.

We studied the local Ru 4d electronic structure of α-RuCl3 by means of polarization dependent xray absorption spectroscopy at the Ru-L2,3 edges. We observed a vanishingly small linear dichroism indicating that electronically the Ru 4d local symmetry is highly cubic. Using full multiplet cluster calculations we were able to reproduce the spectra excellently and to extract that the trigonal splitting of the t2g orbitals is −12 ± 10 meV, i.e. negligible as compared to the Ru 4d spin-orbit coupling constant. Consistent with our magnetic circular dichroism measurements, we found that the ratio of the orbital and spin moments is 2.0, the value expected for a J eff = 1/2 ground state. We have thus shown that as far as the Ru 4d local properties are concerned, α-RuCl3 is an ideal candidate for the realization of Kitaev physics.Geometrically frustrated quantum spin systems are important owing to the fact that frustration often results in a suppression of conventional mean field ground states in favor of more exotic phases of matter. Current research focuses on the effect of spin-orbit coupling (SOC) and the role it plays in the realization of different exotic phases such as unconventional superconductivity or quantum spin liquids [1-3]. Especially, quantum spin liquids can result in topological states with fractional excitations. An important, theoretically solvable model is the Kitaev model with spin-1/2 on a honeycomb lattice, where the coupling between neighboring spins is highly anisotropic with bond-dependent spin interactions. In contrast to spin liquids arising from usual geometrical frustrated spin arrangements, the bond-dependent spin interactions within the Kitaev model frustrate the spin configuration on a single site [4].The search for fractionalized excitations and the identification of a Kitaev spin liquid state has been experimentally quite difficult. Increased attention has been focussed on the honeycomb iridates [5,6], starting from the assumption that large spin-orbit coupling is the leading energy scale in determining the ground state such that the Ir 5d t 2g orbitals are described in terms of J eff = 1/2 and 3/2 orbitals. However, the real iridate systems exhibit trigonal distortion (D trig = 0.1 eV [6]) and a significant itinerant character of the Ir 5d orbitals [7-9], which complicates the electronic ground state. Despite a flurry of both theoretical and experimental studies, the nature of the ground state in honeycomb iridates are being fiercely debated and the occurrence of Kitaev physics is still far from clear.Recently, α-RuCl 3 has been suggested as a promising candidate material for the realization of the Kitaev model [10] and excitations observed via Raman [11,12] and in-elastic neutron scattering [13] have been presented as evidence that α-RuCl 3 may be close to a quantum spin liquid ground state. In the last two years a number of publications discussing the realization of the Kitaev physics in α-RuCl 3 has appeared in literature [3,[14][15][16][17][18][20][21][22][23][24][25][26][27][28][29]...

No abstract

Hybrid devices based on spin‐crossover (SCO)/2D heterostructures grant a highly sensitive platform to detect the spin transition in the molecular SCO component and tune the properties of the 2D material. However, the fragility of the SCO materials upon thermal treatment, light irradiation, or contact with surfaces and the methodologies used for their processing have limited their applicability. Here, an easily processable and robust SCO/2D hybrid device with outstanding performance based on the sublimable SCO [Fe(Pyrz)2] molecule deposited over chemical vapor deposition (CVD) graphene is reported, which is fully compatible with electronics industry protocols. Thus, a novel methodology based on growing an elusive polymorph of [Fe(Pyrz)2] (tetragonal phase) over graphene is developed that allows a fast and effective light‐induced spin transition in the devices (≈50% yield in 5 min) to be detected electrically. Such performance can be enhanced even more when a flexible polymeric layer of poly(methyl methacrylate) is inserted in between the two active components in a contactless configuration, reaching a ≈100% yield in 5 min.

Here the correlation between the chemical shift in X-ray absorption spectroscopy, the geometrical structure and the formal valence state of the Mn atom in mixed-valence manganites are discussed. It is shown that this empirical correlation can be reliably used to determine the formal valence of Mn, using either X-ray absorption spectroscopy or resonant X-ray scattering techniques. The difficulties in obtaining a reliable comparison between experimental XANES spectra and theoretical simulations on an absolute energy scale are revealed. It is concluded that the contributions from the electronic occupation and the local structure to the XANES spectra cannot be separated either experimentally or theoretically. In this way the geometrical and electronic structure of the Mn atom in mixed-valence manganites cannot be described as a bimodal distribution of the formal integer Mn(3+) and Mn(4+) valence states corresponding to the undoped references.

The combination of topological properties and magnetic order can lead to new quantum states and exotic physical phenomena, such as the quantum anomalous Hall (QAH) effect. The size of the magnetic gap in the topological surface states, key for the robust observation of the QAH state, scales with the magnetic moment of the doped 3D topological insulator (TI). The pioneering transition-metal doped (Sb,Bi)2(Se,Te)3 thin films only allow for the observation of the QAH effect up to some 100 mK, despite the much higher magnetic ordering temperatures. On the other hand, high magnetic moment materials, such as rare-earth doped (Sb,Bi)2(Se,Te)3 thin films, show large moments but no long-range magnetic order. Proximity coupling and interfacial effects, multiplied in artificial heterostructures, allow for the engineering of the electronic and magnetic properties. Here, we show the successful growth of high-quality Dy:Bi2Te3/Cr:Sb2Te3 thin film heterostructures. Using x-ray magnetic spectroscopy we demonstrate that high transition temperature Cr:Sb2Te3 can introduce long-range magnetic order in high-moment Dy:Bi2Te3 -up to a temperature of 17 Kin excellent agreement with first-principles calculations, which reveal the origin of the long-range magnetic order in a strong antiferromagnetic coupling between Dy and Cr magnetic moments at the interface extending over several layers. Engineered magnetic TI heterostructures may be an ideal materials platform for observing the QAH effect at liquid He temperatures and above.