Field-induced domain wall propagation: beyond the one-dimensional model

We have investigated numerically the field-driven propagation of perpendicularly magnetized ferromagnetic layers. It was then compared to the historical one-dimensional domain wall (DW) propagation model widely used in spintronics studies of magnetic nanostructures. In the particular regime of layer thickness (h) of the order of the exchange length, anomalous velocity peaks appear in the precessional regime, their shape and position shifting with h. This has also been observed experimentally. Analyses of the simulations show a distinct correlation between the curvature of the DW and the twist of the magnetization vector within it, and the velocity peak. Associating a phenomenological description of this twist with a four-coordinate DW propagation model, we reproduce very well these kinks and show that they result from the torque exerted by the stray field created by the domains on the twisted magnetization. The position of the peaks is well predicted from the DW's first flexural mode frequency, and depends strongly on the layer thickness. Comparison of the proposed model to DW propagation data obtained on dilute semiconductor ferromagnets GaMnAs and GaMnAsP sheds light on the origin of the measured peaks

Determination of the micromagnetic parameters in (Ga,Mn)As using domain theory

The magnetic domain structure and magnetic properties of a ferromagnetic (Ga,Mn)As epilayer with perpendicular magnetic easy-axis are investigated. We show that, despite strong hysteresis, domain theory at thermodynamical equilibrium can be used to determine the micromagnetic parameters. Combining magneto-optical Kerr microscopy, magnetometry and ferromagnetic resonance measurements, we obtain the characteristic parameter for magnetic domains $\lambda_c$, the domain wall width and specific energy, and the spin stiffness constant as a function of temperature. The nucleation barrier for magnetization reversal and the Walker breakdown velocity for field-driven domain wall propagation are also estimated

Zur Kasuistik der totalen Magenexstirpation 1 ) (Oesophagoenterostomie)

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Irreversible magnetization switching using surface acoustic waves

An analytical and numerical approach is developped to pinpoint the optimal experimental conditions to irreversibly switch magnetization using surface acoustic waves (SAWs). The layers are magnetized perpendicular to the plane and two switching mechanisms are considered. In precessional switching, a small in-plane field initially tilts the magnetization and the passage of the SAW modifies the magnetic anisotropy parameters through inverse magneto-striction, which triggers precession, and eventually reversal. Using the micromagnetic parameters of a fully characterized layer of the magnetic semiconductor (Ga,Mn)(As,P), we then show that there is a large window of accessible experimental conditions (SAW amplitude/wave-vector, field amplitude/orientation) allowing irreversible switching. As this is a resonant process, the influence of the detuning of the SAW frequency to the magnetic system's eigenfrequency is also explored. Finally, another - non-resonant - switching mechanism is briefly contemplated, and found to be applicable to (Ga,Mn)(As,P): SAW-assisted domain nucleation. In this case, a small perpendicular field is applied opposite the initial magnetization and the passage of the SAW lowers the domain nucleation barrier.Comment: 11 pages, 4 figure

Deep and shallow electronic states associated to doping, contamination and intrinsic defects in ε-Ga2O3 epilayers

Deep and shallow electronic states in undoped and Si-doped ε-Ga2O3 epilayers grown by MOVPE on c-oriented Al2O3 were investigated by cathodoluminescence, optical absorption, photocurrent spectroscopy, transport measurements, and electron-paramagnetic-resonance. Nominally undoped films were highly resistive, with a room temperature resistivity varying in the range 107- 1013 Ωcm depending on the carrier gas used during growth. Films grown with He carrier were generally more resistive than those grown with H2 carrier and exhibited a Fermi level located at about 0.8 eV below the conduction band edge, which tends to shift deeper with temperature. This can tentatively be attributed to the combined action of deep donors (probably carbon impurities and oxygen vacancies) and deep acceptors (Ga vacancies and related complexes), which compensate residual shallow donors. There are strong experimental hints that nitrogen also behaves as deep acceptor. Room temperature resistivity as low as 0.42 Ωcm and electron concentrations around 1018 cm−3 were obtained by silicon doping. Si was confirmed to act as shallow donor with sufficiently high solubility. A variable range hopping conduction was observed in a wide temperature interval in the n-type layers, and compensation by native acceptors also plays a major role on conduction mechanisms. Previous evaluations of curvature and anisotropy of the conduction band are confirmed, which allows for the estimation of the electron effective mass. The present experimental data are discussed considering the theoretical predictions for point defect formation in the ε-polymorph as well as literature data on extrinsic and intrinsic defects in β-Ga2O3

Transcatheter indirect mitral annuloplasty induces annular and left atrial remodelling in secondary mitral regurgitation

Aims Mitral annuloplasty using the Carillon Mitral Contour System (CMCS) reduces secondary mitral regurgitation (SMR) and leads to reverse left ventricular remodelling. The aim of this study was to evaluate the effect of the CMCS on the mitral valve annulus (MA) and left atrial volume (LAV). Methods and results We retrospectively evaluated the data of all patients treated with the CMCS at our centre. Using transthoracic echocardiography, MA diameters were assessed by measuring the anterolateral to posteromedial extend (ALPM) and the anterior to posterior (AP) dimensions, respectively. Also, LAV and left ventricular end‐diastolic volume (LVEDV) were assessed. Patients were examined at three time points: baseline, at 20–60 days (30dFUP), and at 9–15 months (1yFUP), using paired analysis. From July 2014 until March 2019, 75 cases of severe SMR were treated using CMCS. Cases in which other devices were used in combination (COMBO therapy, n = 35) or in which the device could not be implanted (implant failure, n = 3) were excluded, leaving 37 patients in the present analysis. Analysis at 30dFUP showed a significant reduction of 16% in the mean ALPM diameter (7.27 ± 5.40 mm) and 15% in the AP diameter (6.57 ± 5.33 mm). Analysis of LAV also showed a significant reduction of 21% (36.61 ± 82.67 mL), with no significant change in LVEDV. At 1yFUP, the reduction of both the mean ALPM diameter of 14% (6.24 ± 5.70 mm) and the mean AP diameter of 12% (5.46 ± 4.99 mm) remained significant and stable. The reduction in LAV was also maintained at 23% (37.03 ± 56.91 mL). LAV index was significantly reduced by 17% at 30dFUP (15.44 ± 40.98 mL/m2) and by 13% at 1yFUP (11.56 ± 31.87 mL/m2), respectively. LVEDV index showed no significant change at 30dFUP and a non‐significant 10% reduction at 1yFUP (17.75 ± 58.79 mL/m2). Conclusions The CMCS successfully treats symptomatic SMR with a stable reduction of not only the AP diameter of the MA, but the current study also demonstrates an additional reduction of the ALPM dimension at both 30dFUP and 1yFUP. We have also shown for the first time that LAV and LAV index are significantly reduced at both 30dFUP and 1yFUP and a non‐significant positive remodelling of the LVEDV. This positive left atrial remodelling has not been looked for and demonstrated in earlier randomized studies of CMCS

Coherent manipulation of nitrogen vacancy centers in 4H silicon carbide with resonant excitation

Silicon carbide (SiC) has become a key player in realization of scalable quantum technologies due to its ability to host optically addressable spin qubits and wafer-size samples. Here, we have demonstrated optically detected magnetic resonance (ODMR) with resonant excitation, and clearly identified the ground state energy levels of the NV centers in 4H-SiC. Coherent manipulation of NV centers in SiC has been achieved with Rabi and Ramsey oscillations. Finally, we show the successful generation and characterization of single nitrogen vacancy (NV) center in SiC employing ion implantation. Our results are highlighting the key role of NV centers in SiC as a potential candidate for quantum information processing