Atmospheric plasmoids with 20-30 cm diameter are generated via a high-voltage discharge above a water surface. They ascend in the ambient air and exist autonomously for several hundreds of ...milliseconds. The plasma processes leading to an emission of visible light for more than 350 ms after detachment from the energy supply are still unknown. Visual and spectroscopic high-speed diagnostics with spatial resolution are thus applied. It is shown for the first time that the free-floating body turns to a torus ring to the end of its lifetime, which ascends in air up to more than 1.5 m and radiates longer than 1.5 s in the infrared spectral range, only limited by the structural circumstances in the laboratory. Vortex formation is thus endorsed as being responsible for the structural integrity of the plasma during the autonomous phase. Emission in the optical spectral range (UV-NIR) is limited to the first 500 ms and is governed by radiation from the tap water contents without the influx of ambient air into the plasma. The OH A-X transition is the most intense emission during the entire visible evolution of the plasmoid. Atomic hydrogen emission is observed only during the first 100 ms close to the central electrode (CE) and is highly dynamic, while emission from dissolved salts is detected during the later evolution but is mostly overlaid by a continuum radiation, which is clearly non-thermal. Using the omnipresent OH emission, the optical emission profile of the main plasmoid is shown to be broad in the center and is rotationally symmetric. The radiated energy from the OH radical integrated over the entire plasmoid evolution is less than 100 J, which is about 3% of the total energy dissipated into the plasma. Emission from dissolved sodium is used to track the plasma channel, which connects the main plasmoid to the CE, during its ascension after energy shut-down giving a fourfold ascension velocity compared to the main plasmoid.
We have investigated substitution effects of Ni, Pt, and Pd on phase formation and magnetic properties of D0
-Mn
Ge thin films. We prepared (Mn
M
)
Ge thin films (M = Ni, Pt, Pd) at 650 °C by ...magnetron sputtering on MgO(0 0 1) substrates with x varying from 0.03 to 0.6. For improving the film quality, a Cr(0 0 1) seed layer was employed. The D0
structure formed only for the lowest concentrations of Ni and Pt. Nevertheless, the doped samples showed strong perpendicular magnetic anisotropy up to x = 0.1. For high Ni concentrations, we observed the formation of a soft ferromagnetic Mn
Ni
Ge phase with a Curie temperature of about 230 K, while in samples with high Pt content the antiferromagnet L1
-MnPt phase is formed along with GePt. In contrast, for Pd substitution, the D0
structure is preserved up to x = 0.2, exhibiting strong perpendicular magnetic anisotropy and low saturation magnetization. Interestingly, the coexistence of the D0
-Mn
Ge and a novel D0
-(Mn
Pd
)
Ge phase was revealed, which might have been facilitated by the low lattice mismatch to the Cr(0 0 1) seed layer. With further increase of the Pd concentration, the D0
structure vanishes and mainly the GePd and GePd
phases are present. Overall within the investigated sample series, the saturation magnetization strongly decreases with increasing dopant concentration, offering the possibility to adjust the saturation magnetization in the range between 20 and 100 emu cm
, while still preserving strong perpendicular magnetic anisotropy, which is important for spintronic applications.
