Recent developments have led to an explosion of activity on skyrmions in three-dimensional (3D) chiral magnets. Experiments have directly probed these topological spin textures, revealed their non-trivial properties, and led to suggestions for novel applications. However, in 3D the skyrmion crystal phase is observed only in a narrow region of the temperature-field phase diagram. We show here, using a general analysis based on symmetry, that skyrmions are much more readily stabilized in two-dimensional (2D) systems with Rashba spin-orbit coupling. This enhanced stability arises from the competition between field and easy-plane magnetic anisotropy, and results in a nontrivial structure in the topological charge density in the core of the skyrmions. We further show that, in a variety of microscopic models for magnetic exchange, the required easy-plane anisotropy naturally arises from the same spin-orbit coupling that is responsible for the chiral Dzyaloshinskii-Moriya interactions. Our results are of particular interest for 2D materials like thin films, surfaces and oxide interfaces, where broken surface inversion symmetry and Rashba spin-orbit coupling leads naturally to chiral exchange and easy-plane compass anisotropy. Our theory gives a clear direction for experimental studies of 2D magnetic materials to stabilize skyrmions over a large range of magnetic fields down to T = 0. arXiv:1402.7082v2 [cond-mat.str-el]

The electronic properties of the polar interface between insulating oxides is a subject of great interest 1-3 . An exciting development is the observation of robust magnetism 4-8 at the interface of two non-magnetic materials, LaAlO 3 (LAO) and SrTiO 3 (STO). Here we present a microscopic theory for the formation and interaction of local moments that depends on essential features of the LAO/STO interface. We show that correlation-induced moments arise owing to interfacial splitting of orbital degeneracy. We find that conduction electrons with a gate-tunable Rashba spin-orbit coupling mediate ferromagnetic exchange with a twist. We predict that the zero-field ground state is a long-wavelength spiral. Its evolution in an external field accounts semi-quantitatively for torque magnetometry data 5 and describes qualitative aspects of the scanning superconducting quantum interference device measurements 6 . We make several testable predictions for future experiments.Recent experiments on the LAO/STO interface have seen tantalizing magnetic signals 4-8 , often persisting up to high temperatures ∼100 K. A large magnetization of 0.3-0.4µ B per interface Ti was observed by torque measurements 5 in an external field. In contrast, scanning superconducting quantum interference device (SQUID) experiments 6 found an inhomogeneous state with a dense set of local moments with no net magnetization, only isolated micron-scale ferromagnetic patches. Our goal is to reconcile these seemingly contradictory observations and to gain insight into the itinerant versus local moment nature of the magnetism, the exchange mechanism and the ordered state.LAO and STO are both band insulators, but the TiO 2 layers at the interface are n-doped when LAO is terminated by a LaO + layer. The polar catastrophe 1 arising from a stack of charged LaO + and AlO − 2 layers grown on STO is averted by the transfer of 0.5 electrons per interface Ti. Oxygen vacancies are also known to provide additional electrons at the interface 1 .What is the fate of these electrons at the interface? Transport data suggest that only a small fraction of the electrons (5-10% of the 0.5 electrons per Ti) are mobile 2,9-11 . Interestingly, magnetotransport studies show a large, gate-tunable Rashba spin-orbit coupling (SOC) for these conduction electrons, arising from broken inversion at the interface 12 . Most of the electrons (comparable to 0.5 electrons per Ti) seem to behave like local moments in the magnetic measurements 5,6 discussed above.We propose a microscopic model of electrons in Ti t 2g states at the LAO/STO interface that leads to the following results: local moments form in the top TiO 2 layer owing to correlations, with interfacial splitting of t 2g degeneracy playing a critical role; conduction electrons mediate ferromagnetic double-exchange interactions between the moments; Rashba SOC for the conduction Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA. *e-mail: randeria@mps.ohio-state.edu electrons leads to a Dzyaloshinskii-Moriya inte...

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Nasal drug administration has been used as an alternative route for the systemic availability of drugs restricted to intravenous administration. This is due to the large surface area, porous endothelial membrane, high total blood flow, the avoidance of first-pass metabolism, and ready accessibility. The nasal administration of drugs, including numerous compound, peptide and protein drugs, for systemic medication has been widely investigated in recent years. Drugs are cleared rapidly from the nasal cavity after intranasal administration, resulting in rapid systemic drug absorption. Several approaches are here discussed for increasing the residence time of drug formulations in the nasal cavity, resulting in improved nasal drug absorption. The article highlights the importance and advantages of the drug delivery systems applied via the nasal route, which have bioadhesive properties. Bioadhesive, or more appropriately, mucoadhesive systems have been prepared for both oral and peroral administration in the past. The nasal mucosa presents an ideal site for bioadhesive drug delivery systems. In this review we discuss the effects of microspheres and other bioadhesive drug delivery systems on nasal drug absorption. Drug delivery systems, such as microspheres, liposomes and gels have been demonstrated to have good bioadhesive characteristics and that swell easily when in contact with the nasal mucosa. These drug delivery systems have the ability to control the rate of drug clearance from the nasal cavity as well as protect the drug from enzymatic degradation in nasal secretions. The mechanisms and effectiveness of these drug delivery systems are described in order to guide the development of specific and effective therapies for the future development of peptide preparations and other drugs that otherwise should be administered parenterally. As a consequence, bioavailability and residence time of the drugs that are administered via the nasal route can be increased by bioadhesive drug delivery systems. Although the majority of this work involving the use of microspheres, liposomes and gels is limited to the delivery of macromolecules (e.g., insulin and growth hormone), the general principles involved could be applied to other drug candidates. It must be emphasized that many drugs can be absorbed well if the contact time between formulation and the nasal mucosa is optimized.