Brillouin light scattering studies of planar metallic magnonic crystals

The application of Brillouin light scattering to the study of the spin-wave spectrum of one- and two-dimensional planar magnonic crystals consisting of arrays of interacting stripes, dots and antidots is reviewed. It is shown that the discrete set of allowed frequencies of an isolated nanoelement becomes a finite-width frequency band for an array of identical interacting elements. It is possible to tune the permitted and forbidden frequency bands, modifying the geometrical or the material magnetic parameters, as well as the external magnetic field. From a technological point of view, the accurate fabrication of planar magnonic crystals and a proper understanding of their magnetic excitation spectrum in the GHz range is oriented to the design of filters and waveguides for microwave communication systems

Simultaneous existence of two spin-wave modes in ultrathin Fe/GaAs(001) films studied by Brillouin Light Scattering: experiment and theory

A double-peaked structure was observed in the {\it in-situ} Brillouin Light Scattering (BLS) spectra of a 6 \AA$$ thick epitaxial Fe/GaAs(001) film for values of an external magnetic field $H$, applied along the hard in plane direction, lower than a critical value $H_c\simeq 0.9$ kOe. This experimental finding is theoretically interpreted in terms of a model which assumes a non-homogeneous magnetic ground state characterized by the presence of perperpendicular up/down stripe domains. For such a ground state, two spin-wave modes, namely an acoustic and an optic mode, can exist. Upon increasing the field the magnetization tilts in the film plane, and for $H \ge H_{c}$ the ground state is homogeneous, thus allowing the existence of just a single spin-wave mode. The frequencies of the two spin-wave modes were calculated and successfully compared with the experimental data. The field dependence of the intensities of the corresponding two peaks that are present in the BLS spectra was also estimated, providing further support to the above-mentioned interpretation.Comment: Shortened version (7 pages). Accepted for publication in Physical Review

Telegestión simulada para la enseñanza a estudiantes de medicina sobre la toma de decisiones en gestión en el primer nivel de atención de salud

Introduction: Medical students are poorly prepared in health services management due to the use of traditional teaching methods, developed in theoretical environments with poor active participation. Virtual simulated training is an innovative alternative in the learning process. Objective: This study aimed to determine the knowledge improvement in managerial decision-making amongst medical students at the Universidad Nacional Mayor de San Marcos in Peru, after a virtual simulated training. Methods: A before-after cross-sectional design was undertaken among final year medical students to measure their improvement in management knowledge. The simulation methodology was used as a component of the Medical Externship clinical course in which the administrative dimension of a clinical case such as hypoacusis was considered. Results: Of the 79 participants, 48 (60.8%) were female and the median age was 25 years. There was a median satisfaction level of 3.8 and the performance median score was 17. The median post-test rank scores were higher and statistically significant than pre-test rank scores (p = 0.004); post-test scores for males (p-value = 0.05) and females (p = 0.03) were also statistically higher than pre-test scores. Conclusion: The non-clinical simulation experience improves the knowledge on managerial decision making. It also opens opportunities to work on management issues in clinical courses, providing a comprehensive learning experience. On the other hand, it is an innovative experience where a clinical course adopts a management component.Introducción: Los estudiantes de medicina están poco preparados en gestión de servicios de salud debido al uso de métodos de enseñanza tradicionales, llevados a cabo en entornos teóricos y poco participativos. La formación virtual simulada es una alternativa innovadora en el proceso de aprendizaje. Objetivo: Determinar la mejora en conocimientos sobre la toma de decisiones gerenciales entre los estudiantes de medicina de la Universidad Nacional Mayor de San Marcos en Perú, tras un entrenamiento simulado virtual. Métodos: Estudio de diseño transversal de antes-después en estudiantes de último año de medicina. La metodología de simulación se utilizó como un componente del curso clínico de externado, en el que se consideró la dimensión administrativa de un caso clínico de hipoacusia. Resultados: De los 79 participantes, 48 (60,8%) eran mujeres y la edad media era de 25 años. La mediana del nivel de satisfacción fue de 3,8 y la mediana del rendimiento fue de 17. La mediana de las puntuaciones del post-test fue mayor y estadísticamente significativa en comparación a la del pre-test (p = 0,004); las puntuaciones post-test fueron más altas que las puntuaciones pre-test para los hombres (p = 0,05) y mujeres (p = 0,03). Conclusiones: La experiencia de simulación no clínica logra una mejora significativa en el conocimiento de los participantes. Además, abre oportunidades para trabajar los temas de gestión en los cursos clínicos, proporcionando una experiencia de aprendizaje integral. Por otro lado, es una experiencia innovadora en la que un curso clínico adopta un componente de gestión

Nanopatterning reconfigurable magnetic landscapes via thermally assisted scanning probe lithography

The search for novel tools to control magnetism at the nanoscale is crucial for the development of new paradigms in optics, electronics and spintronics. So far, the fabrication of magnetic nanostructures has been achieved mainly through irreversible structural or chemical modifications. Here, we propose a new concept for creating reconfigurable magnetic nanopatterns by crafting, at the nanoscale, the magnetic anisotropy landscape of a ferromagnetic layer exchange-coupled to an antiferromagnetic layer. By performing localized field cooling with the hot tip of a scanning probe microscope, magnetic structures, with arbitrarily oriented magnetization and tunable unidirectional anisotropy, are reversibly patterned without modifying the film chemistry and topography. This opens unforeseen possibilities for the development of novel metamaterials with finely tuned magnetic properties, such as reconfigurable magneto-plasmonic and magnonic crystals. In this context, we experimentally demonstrate spatially controlled spin wave excitation and propagation in magnetic structures patterned with the proposed method

Reconfigurable spin wave modes in a Heusler magnonic crystal

International audienceWe report on the field evolution of the microwave spin wave modes in magnonic crystals made of square antidot lattices etched in a thin film of the Co2MnSi Heusler alloy and having a lateral size s of 200 nm and an edge-to-edge separation d of 600 or 800 nm. The spin wave modes are investigated combining ferromagnetic resonance, Brillouin light scattering experiments, and micromagnetic simulations of the static and dynamic magnetic states as a function of the applied field. We show that for applied fields ≥10 mT, when the magnetization is quasi-saturated across the crystals, the two samples show similar behavior and the two most intense modes in the spin waves spectra correspond to a mode extending in the channels comprised between the antidot and a mode localized in the region between the antidots. For smaller fields, we observe a difference of the measured spectra as a function of d. This is attributed to the fact that for d = 800 nm, the magnetization remains partially uniform in the channel between the antidots because of the Heusler cubic crystal anisotropy, while for d = 600 nm, the magnetic edge domains around the antidots spread into the channels. Moreover, this anisotropy also allows different remanent states when initializing the crystals with a small magnetic field along two perpendicular directions. This leads to an efficient excitation or extinction of the spin wave modes, making possible to achieve reconfigurable microwave devices exploiting an antidot geometry in a metallic ferromagnetic with a low damping coefficient

Collective spin waves on a nanowire array with step-modulated thickness

10.1088/0022-3727/47/10/105003Journal of Physics D: Applied Physics4710-JPAP

Angular Band Diagrams for Multidirectional Spin Wave Propagation in Square Antidot Lattices‎

By means of a joint experimental and theoretical investigation, we propose an alternative way of describing band properties of collective spin waves (SWs) when considering their propagation direction across a magnonic crystal (in our case, a square antidot lattice, ADL): to build up an angular band diagram, in which frequency is plotted as a function of the angle of SW propagation. Similarly to conventional band diagrams, even in this case different dispersions of different modes give origin to allowed/forbidden bands, related not only to the specific in-plane angle at which they are considered, but also to the SW wavevector magnitude and the ADL constant. We performed Brilluoin light scattering (BLS) measurements on a Permalloy ADL (with a lattice constant of 440 nm), mounted on a two-axis goniometer, which allows us to choose a specific angle of incidence of light as well as to rotate the sample around the surface normal (azimuthal rotation). By changing these angles, it is possible to change the magnitude and/or the in-plane direction of the wavevector of light (and, as a consequence, of the detected SW) [1]. In Fig. 1, we show an example of angular band diagram for a SW with k=1.06×2π/a (corresponding to a light incidence angle of 40 degrees): full circles are the experimental data, lines are the dispersions calculated by means of the dynamical matrix method (DMM) [2]. As apparent in Fig. 1, a minimum gap between the most intense SW modes occurs close to φG=28 degrees: however, this value is critically dependent on the wavevector magnitude (and the lattice constant, if different ADLs are compared). We derive and prove this functional dependence with analitical considerations. We believe that this results are of interest for magnon-spintronic applications where a straight antenna on an ADL is used to emit SWs in any direction (omnidirectional SW emission). References: [1] G. Gubbiotti, F. Montoncello,S. Tacchi, M. Madami, G. Carlotti, L. Giovannini, J. Ding and A. O. Adeyeye, Applied Physics Letters 106, 262406 (2015). [2] L. Giovannini, F. Montoncello, and F. Nizzoli, Physical Review B 75, 024416 (2007)

Structure and magnetism of Fe/Cu(110) thin films

We report on the Structural and magnetic properties of thin Fe films grown on the Cu(1 1 0) surface. In-plane grazing-incidence X-ray diffraction has been Used to Measure the lateral lattice spacing of the Fe films. Complementary information about the structure of the topmost layers has been obtained by means of Auger and photoelectron diffraction. The Fe film grows pseudomorphic with the substrate up to a thickness of about 0.8 nm. The diffraction feature of a new phase is observed at 1.6 nm, with a corresponding interplanar distance close to the bulk body centered cubic (bee) Fe one, which is eventually recovered at higher thickness (6.4 nm). From comparison between X-ray diffraction and photoelectron diffraction, it is suggested that the bcc-like Fe grows on the (1 0 0) surface with its [1 1 0] axis oriented along the [0 0 1] substrate direction. The photoelectron diffraction data also indicate a strong faceting in the [1 1 0] substrate direction. This morphology is believed to contribute to the in-plane uniaxial magnetic anisotropy observed by Kerr effect and Brillouin light scattering from spin waves