We present an experimental and theoretical investigation of the influence of a uniaxial magnetocrystalline anisotropy on the magnetic textures that are formed in a chiral magnetic system. We show that the epitaxially induced tensile stress in MnSi thin films grown on Si (111) creates an easy-plane uniaxial anisotropy. The magnetoelastic shear stress coefficient is derived from SQUID magnetometry measurements in combination with transmission electron microscopy and x-ray diffraction data. Density functional calculations of the magnetoelastic coefficient support the conclusion that the uniaxial anisotropy originates from the magnetoelastic coupling. Theoretical calculations based on a Dzyaloshinskii model that includes an easy-plane anisotropy predict a variety of modulations to the magnetic order that are not observed in bulk MnSi crystals. Evidence for these states is found in the magnetic hysteresis and polarized neutron reflectometry measurements.

A detailed investigation of the magnetization processes in epitaxial MnSi thin film reveals the existence of elliptically distorted skyrmion strings that lie in the plane of the film. We provide proof that the uniaxial anisotropy stabilizes this state over extended regions of the magnetic phase diagram. Theoretical analysis of an observed cascade of first-order phase transitions is based on rig- orous numerical calculations of competing chiral modulations, which shows the existence of helicoids, elliptic skyrmions, and cone phases

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Helical magnetic order in MnSi thin films

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The low temperature photoluminescence properties of InAs/InP self-assembled quantum dots are investigated in magnetic fields up to 17 T. The zero field spectrum exhibits a number of inhomogeneously broadened peaks similar to the highly excited spectrum of InAs/GaAs quantum dots in which emission from excited states can be observed. However, for InAs/InP dots, application of a magnetic field in the Faraday configuration reveals only weak diamagnetic shifts, thus proving that the transitions originate from zero angular momentum states consistent with ground state emission from distinct families of islands present in the sample. The diamagnetic shift is observed to increase as the thickness of the island family increases. Calculations performed assuming a flat disc geometry show that the latter effect can be accounted for by the change in carrier effective mass as the dot thickness increases.

The annular dark field (ADF) image contrast of GaNyAs1−y (y = 0.029 and 0.045) epitaxial layers on (100) GaAs substrates was studied with a scanning transmission electron microscope (STEM) as a function of ADF detector inner semi-angles ranging from 28 to 90 mrad. Contradictory to the compositional contrast prediction of ADF-STEM image intensity, the lower average atomic number strained GaNyAs1−y layers were found to be brighter than the higher average atomic number GaAs for an ADF detector semi-angle up to 65 mrad. Multislice simulations reveal that the displacement around substitutional N atoms plays a crucial role in the observed ADF-STEM contrast, while the contribution to the contrast due to misfit strain between GaNyAs1−y and GaAs is small.

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