Large asymmetry in the magnetoresistance loops of ferromagnetic nanostrips induced by Surface Acoustic Waves.

In this work we show that Surface Acoustic Waves (SAW) can induce a very large asymmetry in the magnetoresistance loop of an adjacent ferromagnetic nanostrip, making it look as if it had exchange bias. The Surface Acoustic Wave induces a DC voltage in the ferromagnetic nanostrip. For measurements at constant current, this DC voltage makes the AMR loop asymmetric. In a series of different electrical experiments, we disentangle two different contributions to the induced DC voltage. One of them is independent on the external magnetic field and it is likely due to the acoustoelectric effect. A second contribution depends on the external magnetic field and it is a rectified voltage induced in the piezoelectric substrate as a response to the magnetization dynamics in the magnetostrictive nanostrip. The large asymmetry in the magnetoresistance loop reported in this work is a manifestation of an effective transfer of energy from the SAW to the magnetization dynamics, a mechanism that has been very recently appointed as a possible mean to harvest energy from a heat source.

Toward Understanding Complex Spin Textures in Nanoparticles by Magnetic Neutron Scattering.

In the quest to image the three-dimensional magnetization structure we show that the technique of magnetic small-angle neutron scattering (SANS) is highly sensitive to the details of the internal spin structure of nanoparticles. By combining SANS with numerical micromagnetic computations we study the transition from single-domain to multidomain behavior in nanoparticles and its implications for the ensuing magnetic SANS cross section. Above the critical single-domain size we find that the cross section and the related correlation function cannot be described anymore with the uniform particle model, resulting, e.g., in deviations from the well-known Guinier law. In the simulations we identify a clear signature for the occurrence of a vortexlike spin structure at remanence. The micromagnetic approach to magnetic SANS bears great potential for future investigations, since it provides fundamental insights into the mesoscale magnetization profile of nanoparticles.

Magnetization process of a ferromagnetic nanostrip under the influence of a surface acoustic wave.

Surface Acoustic Waves (SAW) are one of the possible solutions to target the challenges faced by modern spintronic devices. The stress carried by the SAW can decrease the current required to achieve magnetic switching or domain wall movement by spin transfer torque. Although the last decade has produced very relevant results in this field, it is still important to study the effects of a SAW on the basic unit of many spintronic devices, a ferromagnetic nanostrip. In this work, we perform a complete set of measurements and simulations to characterize the magnetization process of a Ni nanostrip under the influence of a SAW. We find that the SAW increases the mobility and the depinning ability of the magnetic domain walls and consequently, promotes a sharper approach to saturation and substantially decreases coercivity. We have also found other two interesting effects. When the SAW has sufficient energy, is able to trigger irreversible transitions even before switching the direction of the external magnetic field. Additionally, we have found that the magnetization process depends on the direction of the travelling SAW.

Publisher Correction: Small-angle neutron scattering modeling of spin disorder in nanoparticles.

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Small-angle neutron scattering modeling of spin disorder in nanoparticles.

Magnetic small-angle neutron scattering (SANS) is a powerful technique for investigating magnetic nanoparticle assemblies in nonmagnetic matrices. For such microstructures, the standard theory of magnetic SANS assumes uniformly magnetized nanoparticles (macrospin model). However, there exist many experimental and theoretical studies which suggest that this assumption is violated: deviations from ellipsoidal particle shape, crystalline defects, or the interplay between various magnetic interactions (exchange, magnetic anisotropy, magnetostatics, external field) may lead to nonuniform spin structures. Therefore, a theoretical framework of magnetic SANS of nanoparticles needs to be developed. Here, we report numerical micromagnetic simulations of the static spin structure and related unpolarized magnetic SANS of a single cobalt nanorod. While in the saturated state the magnetic SANS cross section is (as expected) determined by the particle form factor, significant deviations appear for nonsaturated states; specifically, at remanence, domain-wall and vortex states emerge which result in a magnetic SANS signal that is composed of all three magnetization Fourier components, giving rise to a complex angular anisotropy on a two-dimensional detector. The strength of the micromagnetic simulation methodology is the possibility to decompose the cross section into the individual Fourier components, which allows one to draw important conclusions regarding the fundamentals of magnetic SANS.

Skyrmions with Attractive Interactions in an Ultrathin Magnetic Film.

We determined the parameters of a classical spin Hamiltonian describing an Fe monolayer on Pd(111) surface with a Pt_{1-x}Ir_{x} alloy overlayer from ab initio calculations. While the ground state of the system is ferromagnetic for x=0.00, it becomes a spin spiral state as Ir is intermixed into the overlayer. Although the Dzyaloshinsky-Moriya interaction is present in the system, we will demonstrate that the frustrated isotropic exchange interactions play a prominent role in creating the spin spiral state, and these frustrated couplings lead to an attractive interaction between Skyrmions at short distances. Using spin dynamics simulations, we show that under these conditions the individual Skyrmions form clusters, and that these clusters remain stable at finite temperature.

Direct observation of magnetic metastability in individual iron nanoparticles.

X-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism is used to study the magnetic properties of individual iron nanoparticles with sizes ranging from 20 down to 8 nm. While the magnetocrystalline anisotropy of bulk iron suggests superparamagnetic behavior in this size range, ferromagnetically blocked particles are also found at all sizes. Spontaneous transitions from the blocked state to the superparamagnetic state are observed in single particles and suggest that the enhanced magnetic energy barriers in the ferromagnetic particles are due to metastable, structurally excited states with unexpected life times.

Trasplante dental autógeno: investigación documental / Autogenous dental transplantation: documentary research

La extracción dental es la remoción quirúrgica de una pieza dental. Las causas más comunes de extracción son: piezas que no pueden ser restauradas, que se encuentran retenidas, fracturadas o asociadas con una formación quística o dientes que se ubican en la línea de una fractura o en una zona que recibirá radiación. Este tratamiento conduce inevitablemente a la formación de una brecha edéntula, para lo cual en la mayoría de los casos se indica un tratamiento protésico o implantológico, con la finalidad de restaurar la función masticatoria y estética. El autotransplante dental es el procedimiento quirúrgico que se convierte en una alternativa para solucionar problemas de pérdida dental, e incluso volver innecesarios los tratamientos antes mencionados. La historia de la Odontología refiere casos de trasplantes dentales que se remontan veinte siglos atrás, eran procedimientos empíricos y actualmente la técnica ha mejorado de forma notable. Es importante conocer acerca del trasplante dental, puesto que es del interés del clínico ofrecer diversas alternativas de tratamiento a sus pacientes, muchos de los cuales no encuentran en la prótesis una solución satisfactoria, y no pueden acceder a un tratamiento de implantes dentales endósticos. El trasplante dental autógeno se vuelve una posibilidad de resolver los problemas de ausencia dental y minimizar el impacto psicológico de la pérdida dental, especialmente cuando involucra dientes anteriores. En este trabajo, se exponen las diferentes indicaciones y contraindicaciones establecidas por muchos investigadores, en conjunto con las técnicas quirúrgicas detalladas por diferentes autores. Además, se dan a conocer las consideraciones previas a la intervención quirúrgica y el manejo postoperatorio. El objetivo perseguido por medio de la realización de este trabajo es hacer una recopilación de material bibliográfico acerca del autotransplante dental, con la finalidad de dar a conocer las posibilidades y la factibilidad de realizar este tratamiento, al igual que las posibles complicaciones que puedan presentarse.

Tooth extraction is the surgical removal of a tooth. The most common causes of extraction are: pieces that cannot be restored, that are retained, fractured or associated with a cystic formation or teeth that are located in the line of a fracture or in an area that will receive radiation. This treatment inevitably leads to the formation of an edentulous gap, for which in most cases a prosthetic or implant treatment is indicated, in order to restore the masticatory and aesthetic function. Dental autotransplantation is the surgical procedure that becomes an alternative to solve problems of tooth loss, and even make the aforementioned treatments unnecessary. The history of Dentistry refers to cases of dental transplants dating back twenty centuries, they were empirical procedures and currently the technique has improved significantly. It is important to know about dental transplantation, since it is in the interest of the clinician to offer various treatment alternatives to their patients, many of whom do not find a satisfactory solution in the prosthesis, and cannot access endosteal dental implant treatment. Autogenous dental transplantation becomes a possibility to solve the problems of dental absence and minimize the psychological impact of tooth loss, especially when it involves anterior teeth. In this work, the different indications and contraindications established by many researchers are exposed, together with the surgical techniques detailed by different authors. In addition, the considerations prior to surgical intervention and postoperative management are disclosed. The objective pursued by carrying out this work is to compile a collection of bibliographic material about dental autotransplantation, in order to publicize the possibilities and feasibility of performing this treatment, as well as the possible complications that may arise.