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

The Influence of Magnetic Domain Walls on Longitudinal and Transverse Magnetoresistance in Tensile Strained (Ga,Mn)As Epilayers

We present a theoretical analysis of recent experimental measurements of magnetoresistance in (Ga,Mn)As epilayers with perpendicular magnetic anisotropy. The model reproduces the field-antisymmetric anomalies observed in the longitudinal magnetoresistance in the planar geometry (magnetic field in the epilayer plane and parallel to the current density), as well as the unusual shape of the accompanying transverse magnetoresistance. The magnetoresistance characteristics are attributed to circulating currents created by the presence of magnetic domain walls

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

Reversal of diastereoselectivity in the synthesis of Peptidomimetic 3‑Carboxamide-1,4-benzodiazepin-5-ones

Enantiopure 3-carboxamide-1,4-benzodiazepin-5-ones were synthesized via the Ugi reaction followed by the Staudinger/aza-Wittig or reduction reactions in only two steps. A complete reversal of diastereoselectivity was achieved depending on the cyclization methodology employed. The different orientation of the C3 substituent in our 3-substituted 1,4-benzodiazepin-5-ones with respect to the most studied 1,4-benzodiazepin-2-ones makes them complementary in the development of new drugs because the primary source of binding selectivity of 1,4-benzodiazepines is the selective recognition of ligand conformations by the receptor.Ministerio de Economía y Competitividad, Spain (Project CTQ2012-31611), Junta de Castilla y León, Consejería de Educación y Cultura y Fondo Social Europeo (Project BU246A12-1) and the European Commission, Seventh Framework Programme (Project SNIFFER FP7-SEC-2012-312411)

Integrated Ugi-Based Assembly of Functionally, Skeletally, and Stereochemically Diverse 1,4-Benzodiazepin-2-ones

A practical, integrated and versatile U-4CR-based assembly of 1,4-benzodiazepin-2-ones exhibiting functionally, skeletally, and stereochemically diverse substitution patterns is described. By virtue of its convergence, atom economy, and bond-forming efficiency, the methodology documented herein exemplifies the reconciliation of structural complexity and experimental simplicity in the context of medicinal chemistry projects.This work was financially supported by the Galician Government (Spain), Projects: 09CSA016234PR and GPC-2014-PG037. J.A. thanks FUNDAYACUCHO (Venezuela) for a predoctoral grant and Deputación da Coruña (Spain) for a postdoctoral research grant. A.N.-V. thanks the Spanish government for a Ramón y Cajal research contract

Domain wall dynamics in annealed GaMnAs epilayers

4th International School and Conference on Spintronics and Quantum Information Technology (Spintech IV), Maui, HI, JUN 17-22, 2007International audienceWe study magnetic field-driven domain wall motion in a GaMnAs thin film. The velocity is measured as function of the applied field. It varies over 6 orders of magnitude in a field range of 2.5 mT. Two regimes are identified. At low field, the domain wall motion follows a creep regime: it is controlled by defects and the domain wall velocity increases exponentially with the applied field. At higher fields, the domain wall motion follows a depinning regime: pinning defects are less efficient and the wall velocity increases linearly with the field. The highest measured domain wall velocity is 14 ms(-1)

Magnetic domain patterns in as-grown and annealed (Ga,Mn)As epilayers with perpendicular easy axis

International audienceMagnetic properties of ferromagnetic (GaMn)As epilayers grown with tensile strain are investigated using combined experimental techniques including Kerr microscopy, transport measurements, and SQUID magnetometry. We show that post-growth annealing substantially increases the Curie temperature, strengthens the perpendicular anisotropy, weakens the in-plane anisotropy and drastically changes the magnetic domain pattern

Unusual domain-wall motion in ferromagnetic semiconductor films with tetragonal anisotropy

International audienceMagnetic field-driven domain-wall propagation in the flow regime is investigated in (Ga, Mn) As ferromagnetic semiconductor layers. Square-shape magnetic domains with an unexpected orientation of their edges, at pi/8 with respect to the anisotropy axes, are found. This is shown to arise from the effect of tetragonal magnetic anisotropy on domain-wall dynamics. Using a one-dimensional model for domain-wall motion and modeling domain growth by contour dynamics the shape and orientation of domains and their field range for existence are well reproduced. These results point to the key role of the vectorial nature of the order parameter in the dynamics of ferromagnetic domains

(Ga,Mn)As layers with perpendicular anisotropy: a study of magnetic domain patterns

International audienceThe magnetic domain pattern in (Ga,Mn)As layers with perpendicular magnetic easy-axis is studied by Kerr microscopy at various temperatures. We investigate the effect of post-growth annealing. As-grown samples exhibit a strongly anisotropic domain growth with dendritic-like expansion of domains along the directions. For annealed samples, the density of nucleation centers is decreased and domain wall propagation is more isotropic. Two kinds of pinning centers are observed in annealed samples: line-like defects that strongly hinder domain wall propagation and point-like defects with a density of a few 10(5) cm(-2)

Experimental determination of domain wall width and spin stiffness constant in ferromagnetic (Ga,Mn)As with perpendicular easy axis

13th International Conference on Modulated Semiconductor Structures (MSS13)/17th International Conference on Electronic Properties of 2-Dimensional Systems, Genova, ITALY, JUL 15-20, 2007International audienceThe magnetic domain structure and hysteresis cycles of (Ga,Mn)As are investigated using magneto-optical imaging. The anisotropy constants and the magnetization are obtained from ferromagnetic resonance and SQUID magnetometry measurements, respectively. The experimental data are analyzed using domain theory for ferromagnetic films with strong uniaxial anisotropy. We obtain lower and upper boundaries for the micromagnetic parameters: the domain wall specific energy, the domain wall width and the spin stiffness constant. (c) 2007 Elsevier B.V. All rights reserved