Pinning dependent field driven domain wall dynamics and thermal scaling in an ultrathin Pt/Co/Pt magnetic film

Magnetic field-driven domain wall motion in an ultrathin Pt/Co(0.45nm)/Pt ferromagnetic film with perpendicular anisotropy is studied over a wide temperature range. Three different pinning dependent dynamical regimes are clearly identified: the creep, the thermally assisted flux flow and the depinning, as well as their corresponding crossovers. The wall elastic energy and microscopic parameters characterizing the pinning are determined. Both the extracted thermal rounding exponent at the depinning transition, $\psi=$0.15, and the Larkin length crossover exponent, $\phi=$0.24, fit well with the numerical predictions.Comment: 5 pages, 4 figure

Dynamic Formation of Metastable Intermediate State Patterns in Type-I Superconductors

Structure of the intermediate state in type-I superconducting lead (Pb) is shown to be very sensitive to the ramp rate of an applied magnetic field. The configurations of resulting static patterns depend sensitively on the shape of the specimen. In particular, geometric barrier, present in the samples with rectangular cross-section, plays an important role in determining the sharp boundary between the phases of different topology. We propose that seemingly laminar (stripe) pattern obtained as a result of the fast field ramp is simply an imprint left behind by the fast-moving flux tubes. Our results confirm that flux tube phase is topologically favorable.Comment: to be presented at LT-25 (Amsterdam, 2008

Field-Driven Domain-Wall Dynamics in GaMnAs Films with Perpendicular Anisotropy

We combine magneto-optical imaging and a magnetic field pulse technique to study domain wall dynamics in a ferromagnetic (Ga,Mn)As layer with perpendicular easy axis. Contrary to ultrathin metallic layers, the depinning field is found to be smaller than the Walker field, thereby allowing for the observation of the steady and precessional flow regimes. The domain wall width and damping parameters are determined self-consistently. The damping, 30 times larger than the one deduced from ferromagnetic resonance, is shown to essentially originate from the non-conservation of the magnetization modulus. An unpredicted damping resonance and a dissipation regime associated with the existence of horizontal Bloch lines are also revealed

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

Current Induced Fingering Instability in Magnetic Domain Walls

The shape instability of magnetic domain walls under current is investigated in a ferromagnetic (Ga,Mn)(As,P) film with perpendicular anisotropy. Domain wall motion is driven by the spin transfer torque mechanism. A current density gradient is found either to stabilize domains with walls perpendicular to current lines or to produce finger-like patterns, depending on the domain wall motion direction. The instability mechanism is shown to result from the non-adiabatic contribution of the spin transfer torque mechanism.Comment: 5 pages, 3 figures + supplementary material

Treatment of complex fractures of the distal radius: a prospective randomised comparison of external fixation 'versus' locked volar plating

The traditional treatment of severely impacted fractures of the distal radius involves bridging external fixation and maintaining reduction by applying continuous traction. The recent technique using fixed-angle screws within volar plates is reported restore the radial length and the articular profile whilst avoiding joint distraction. It is also believed to produce better and quicker clinical results. To test these claims, we carried out a randomised controlled comparison of the efficiency of external fixation (EF) \u27versus\u27 open reduction and internal fixation (ORIF) in treating severely impacted fractures of the distal radius. A total of 39 patients were treated with EF, eventually associated with percutaneous pinning, whereas 36 underwent ORIF with a locked volar plate. There was no significant difference in the two groups with regard to changes in the ulnar variance. Articular reduction was poor in two patients in the EF group with residual step-offs exceeding 2mm; another patient of the EF group suffered a secondary loss of reduction, healing with a severe articular malunion (>2mm). By contrast, articular reduction was satisfactory in all the patients of the ORIF group. The clinical results on the Green and O\u27Brien rating were significantly better in the ORIF group than in the EF group (p<0.01 at 6 weeks, p<0.05 at 6 months). Nevertheless, open reduction and volar plating did not yield better subjective results than EF. However, although not statistically significant, patients treated by ORIF seemed to resume their usual activities quicker than those treated with EF, suggesting that this technique may be adapted to a greater extent in the case of active, young individuals

Domain-wall roughness in GdFeCo thin films: crossover length scales and roughness exponents

Domain-wall dynamics and spatial fluctuations are closely related to each other and to universal features of disordered systems. Experimentally measured roughness exponents characterizing spatial fluctuations have been reported for magnetic thin films, with values generally different from those predicted by the equilibrium, depinning and thermal reference states. Here, we study the roughness of domain walls in GdFeCo thin films over a large range of magnetic field and temperature. Our analysis is performed in the framework of a model considering length-scale crossovers between the reference states, which is shown to bridge the differences between experimental results and theoretical predictions. We also quantify for the first time the size of the depinning avalanches below the depinning field at finite temperatures.Comment: 10 pages, 6 figures. The first two authors contributed equally to this wor

Nucleation and Collapse of the Superconducting Phase in Type-I Superconducting Films

The phase transition between the intermediate and normal states in type-I superconducting films is investigated using magneto-optical imaging. Magnetic hysteresis with different transition fields for collapse and nucleation of superconducting domains is found. This is accompanied by topological hysteresis characterized by the collapse of circular domains and the appearance of lamellar domains. Magnetic hysteresis is shown to arise from supercooled and superheated states. Domain-shape instability resulting from long-range magnetic interaction accounts well for topological hysteresis. Connection with similar effects in systems with long-range magnetic interactions is emphasized

Universal Critical Exponents of the Magnetic Domain Wall Depinning Transition

Magnetic field driven domain wall dynamics in a ferrimagnetic GdFeCo thin film with perpendicular magnetic anisotropy is studied using low temperature magneto-optical Kerr microscopy. Measurements performed in a practically athermal condition allow for the direct experimental determination of the velocity ($\beta = 0.30 \pm 0.03$) and correlation length ($\nu = 1.3 \pm 0.3$) exponents of the depinning transition. The whole family of exponents characterizing the transition is deduced, providing evidence that the depinning of magnetic domain walls is better described by the quenched Edwards-Wilkinson universality class.Comment: 6 pages, 3 figures. Ancillary Material with 10 pages and 4 figures is also include