Magnetic patterning of (Ga,Mn)As by hydrogen passivation

We present an original method to magnetically pattern thin layers of (Ga,Mn)As. It relies on local hydrogen passivation to significantly lower the hole density, and thereby locally suppress the carrier-mediated ferromagnetic phase. The sample surface is thus maintained continuous, and the minimal structure size is of about 200 nm. In micron-sized ferromagnetic dots fabricated by hydrogen passivation on perpendicularly magnetized layers, the switching fields can be maintained closer to the continuous film coercivity, compared to dots made by usual dry etch techniques

Macrospin limit and configurational anisotropy in nanoscale Permalloy triangles

In Permalloy submicron triangles, configurational anisotropy - a higher-order form of shape anisotropy - yields three equivalent easy axes, imposed by the structures' symmetry order. Supported by micromagnetic simulations, an experimental method was devised to evaluate the nanostructure dimensions for which a Stoner-Wohlfarth type of reversal could be used to describe this particular magnetic anisotropy. In this regime, a straightforward procedure using an in-plane rotating field allowed us to quantify experimentally the six-fold anisotropy fields for triangles of different thicknesses and sizes

Tuning the ferromagnetic properties of hydrogenated GaMnAs

Hydrogenation and posthydrogenation annealings have been used as a very efficient tool to tune the hole density over a wide range, at fixed magnetic moment concentration, in thin GaMnAs layers. Reduction of the hole density resulted in strong modifications of their ferromagnetic properties. In particular, we observed in magnetotransport experiments the decrease of the Curie temperature, along with modifications of the magnetic anisotropy, a behavior consistent with the mean-field theory

A national survey of New Zealand secondary schools Physical Education programs implementation of the teaching personal and social responsibility (TPSR) model

All New Zealand secondary schools (370) received a 38-item survey examining their use of the Teaching Personal and Social Responsibility model (TPSR) within their physical education programs. A total of 148 schools (40%) responded of which 79 reported that they were teaching TPSR in their physical education programs. On average, the teachers using TPSR (158) had taught physical education for 4.8 years. While some were in their first year of teaching TPSR, 69.7% reported that they had been using the model for over two years and 37.8% for more than five. Teachers indicated that they had high levels of knowledge of, and confidence in, using TPSR. When exploring how teachers implemented TPSR it was found that many did not follow the daily program format consistently when teaching TPSR-based lessons. Almost 70% of teachers using TPSR had taught it in combination with Sport Education and most considered the combination to be highly successful. Teachers generally believed that TPSR-based teaching led to better behaved, more supportive students who were more able to be self-directed learners. They also believed TPSR resulted in improved learning in physical education and generated positive outcomes in other areas of the schools.Todas las escuelas de secundaria neozelandesas (370) recibieron un cuestionario de 38 preguntas destinado a examinar la utilización del modelo Enseñanza de la Responsabilidad Personal y Social (TPSR) en sus programas de Educación Física (EF). Respondieron 148 escuelas (40%), de las cuales 79 indicaron que sí lo usaban. Como promedio, los profesores que aplicaban el TPSR (158) llevaban dando clase de EF 4,8 años. Aunque algunos indicaron que era el primer año que estaban desarrollándolo, el 69.7% afirmó llevar haciéndolo más de dos años, y el 37.8% más de cinco. También, los profesores dijeron tener un nivel alto de conocimiento del TPSR y una gran confianza en su utilización.Al explorar el modo en que los profesores aplicaban el modelo, se observó que, cuando llevaban a cabo sus lecciones basadas en TPSR, muchos no seguían de forma sistemática el formato de programa diario.Casi un 70% de los profesores que usaban el TPSR lo habían enseñado en combinación con la Educación Deportiva, y la mayoría consideraba dicha combinación muy exitosa. En general, creían que la enseñanza basada en el TPSR conllevaba una mejora en el comportamiento de los alumnos que se hacían más comprensivos, solidarios y eran más capaces de auto-dirigir su aprendizaje. También creían que el TPSR mejoraba el aprendizaje en EF y generaba resultados positivos en otras áreas escolares

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

Acoustic solitons: A robust tool to investigate the generation and detection of ultrafast acoustic waves

International audienceSolitons are self-preserving traveling waves of great interest in nonlinear physics but hard to observe experimentally. In this report an experimental setup is designed to observe and characterize acoustic solitons in a GaAs(001) substrate. It is based on careful temperature control of the sample and an interferometric detection scheme. Ultrashort acoustic solitons, such as the one predicted by the Korteweg–de Vries equation, are observed and fully characterized. Their particlelike nature is clearly evidenced and their unique properties are thoroughly checked. The spatial averaging of the soliton wave front is shown to account for the differences between the theoretical and experimental soliton profile. It appears that ultrafast acoustic experiments provide a precise measurement of the soliton velocity. It allows for absolute calibration of the setup as well as the response function analysis of the detection layer. Moreover, the temporal distribution of the solitons is also analyzed with the help of the inverse scattering method. It shows how the initial acoustic pulse profile which gives birth to solitons after nonlinear propagation can be retrieved. Such investigations provide a new tool to probe transient properties of highly excited matter through the study of the emitted acoustic pulse after laser excitation