Direct observation of cycloidal spin modulation and field-induced transition in N\'eel-type skyrmion-hosting VOSe2_2O5_5

We investigate the spin rotational structure of magnetic skyrmions in a tetragonal polar magnet VOSe2O5 via polarized small-angle neutron scattering (SANS). Spin polarization analysis of the scattered neutrons provides consistent evidence for the cycloidal spin modulation in all the incommensurate phases at zero and non-zero magnetic field along the c axis, including the triangular skyrmion-lattice phase. In the vicinity of the skyrmion phase, we performed extensive SANS measurements to unravel a field-induced incommensurate phase (IC-2 state). We discuss the possibility of anisotropic double-q state as an alternative spin structure to provisional square skyrmion-lattice state.Comment: 27 pages, 5 figure

[11C]-DPA-713 and [18F]-DPA-714 as New PET Tracers for TSPO: A Comparison with [11C]-(R)-PK11195 in a Rat Model of Herpes Encephalitis

Background: Activation of microglia cells plays an important role in neurological diseases. Positron emission tomography (PET) with [C-11]-(R)-PK11195 has already been used to visualize activated microglia cells in neurological diseases. However, [C-11]-(R)-PK11195 may not possess the required sensitivity to visualize mild neuroinflammation. In this study, we evaluated the PET tracers [C-11]-DPA-713 and [F-18]-DPA-714 as agents for imaging of activated microglia in a rat model of herpes encephalitis. Materials and Methods: Rats were intranasally inoculated with HSV-1. On day 6 or 7 after inoculation, small animal PET studies were performed to compare [C-11]-(R)-PK11195, [C-11]-DPA-713, and [F-18]-DPA-714. Results: Uptake of [C-11]-DPA-713 in infected brain areas was comparable to that of [C-11]-(R)-PK11195, but [C-11]-DPA-713 showed lower non-specific binding. Non-specific uptake of [F-18]-DPA-714 was lower than that of [C-11]-(R)-PK11195. In the infected brain, total [F-18]-DPA-714 uptake was lower than that of [C-11]-(R)-PK11195, with comparable specific uptake. Conclusions: [C-11]-DPA-713 may be more suitable for visualizing mild inflammation than [C-11]-(R)-PK11195. In addition, the fact that [F-18]-DPA-714 is an agonist PET tracer opens new possibilities to evaluate different aspects of neuroinflammation. Therefore, both tracers warrant further investigation in animal models and in a clinical setting

Advances in ab-initio theory of Multiferroics. Materials and mechanisms: modelling and understanding

Within the broad class of multiferroics (compounds showing a coexistence of magnetism and ferroelectricity), we focus on the subclass of "improper electronic ferroelectrics", i.e. correlated materials where electronic degrees of freedom (such as spin, charge or orbital) drive ferroelectricity. In particular, in spin-induced ferroelectrics, there is not only a {\em coexistence} of the two intriguing magnetic and dipolar orders; rather, there is such an intimate link that one drives the other, suggesting a giant magnetoelectric coupling. Via first-principles approaches based on density functional theory, we review the microscopic mechanisms at the basis of multiferroicity in several compounds, ranging from transition metal oxides to organic multiferroics (MFs) to organic-inorganic hybrids (i.e. metal-organic frameworks, MOFs)Comment: 22 pages, 9 figure

Creation and annihilation of topological meron pairs in in-plane magnetized films

Merons which are topologically equivalent to one-half of skyrmions can exist only in pairs or groups in two-dimensional (2D) ferromagnetic (FM) systems. The recent discovery of meron lattice in chiral magnet Co8Zn9Mn3 raises the immediate challenging question that whether a single meron pair, which is the most fundamental topological structure in any 2D meron systems, can be created and stabilized in a continuous FM film? Utilizing winding number conservation, we develop a new method to create and stabilize a single pair of merons in a continuous Py film by local vortex imprinting from a Co disk. By observing the created meron pair directly within a magnetic field, we determine its topological structure unambiguously and explore the topological effect in its creation and annihilation processes. Our work opens a pathway towards developing and controlling topological structures in general magnetic systems without the restriction of perpendicular anisotropy and Dzyaloshinskii-Moriya interaction