P. Landeros

Angular dependence of coercivity in magnetic nanotubes

The nucleation field for infinite magnetic nanotubes, in the case of a magnetic field applied parallel to the long axis of the tubes, is calculated as a function of their geometric parameters and compared with those produced inside the pores of anodic alumina membranes by atomic layer deposition. We also extended this result to the case of an angular dependence. We observed a transition from curling-mode rotation to coherent-mode rotation as a function of the angle in which the external magnetic field is applied. Finally, we observed that the internal radii of the tubes favors the magnetization curling reversal.

Domain wall motion on magnetic nanotubes

In this paper the dynamical regimes of the motion of domain walls in magnetic nanotubes are studied theoretically. We compare results obtained with a simplified model of the magnetic energy with a detailed one that includes an exact treatment of the dipolar field. We demonstrate that the proper inclusion of dipolar effects changes qualitatively the mobility of a vortex domain wall driven by an applied magnetic field. We report that magnetic nanotubes display the characteristic phenomenology of domain wall motion: at low fields we find a steady motion with almost constant mobility (velocity/field) up to a critical field, where steady motion breaks out and a precessional motion appears. It is also found that the initial chirality of a vortex domain wall determines the dynamic regime of the motion near the Walker critical field.

A detailed analysis of dipolar interactions in arrays of bi-stable magnetic nanowires

The investigation of the role of interactions in magnetic wire arrays is complex and often involves substantial simplifications. In this paper analytical expressions taking into consideration the geometry of the wires and dipolar interactions between them have been obtained. An expansion of these terms, at first order, can be easily evaluated and shows a good agreement with the total expression for the energy. The extent of the interwire magnetostatic coupling has also been investigated, and it is shown that the number of wires required to reach a size independent magnetic state in the array strongly depends on the relative magnetic orientation of the wires.

Magnetic phase diagrams of barcode-type nanostructures

The magnetic configurations of barcode-type magnetic nanostructures consisting of alternate ferromagnetic and nonmagnetic layers arranged within a multilayer nanotube structure are investigated as a function of their geometry. Based on a continuum approach we have obtained analytical expressions for the energy which lead us to obtain phase diagrams giving the relative stability of characteristic internal magnetic configurations of the barcode-type nanostructures.

Magnetostatic fields in tubular nanostructures

The non-uniform magnetostatic field produced by the equilibrium and non-equilibrium magnetic states of magnetic nanotubes has been investigated theoretically. We consider magnetic fields produced by actual equilibrium states and transverse and vortex domain walls confined within the nanostructure. Our calculations allow us to understand the importance of the magnetostatic field in nanomagnetism, which is frequently considered as a uniform field. Moreover, our results can be used as a basis for future research of other properties, such as the investigation of spin waves when domain walls are present, or the motion of a magnetic particle near a magnetic field.

Vortex core size in interacting cylindrical nanodot arrays

The effect of dipolar interactions among cylindrical nanodots, with a vortex–core magnetic configuration, is analyzed by means of analytical calculations. The cylinders are placed in a N × N square array in two configurations—cores oriented parallel to each other and with antiparallel alignment between nearest neighbors. Results comprise the variation in the core radius with the number of interacting dots, the distance between them and dot height. The dipolar interdot coupling leads to a decrease (increase) of the core radius for parallel (antiparallel) arrays.

Oersted field assisted magnetization reversal in cylindrical core-shell nanostructures

A method to manipulate magnetization reversal in core-shell nanostructures is presented. The focus is on cylindrical multilayer structures comprising of an inner conductor wire covered by two shells: (i) an intermediate non-conducting and non-magnetic shell and (ii) a nanotube made of an outer ferromagnetic layer. The properties of the magnetization reversal of the ferromagnetic phase are investigated when a circular Oersted field is generated by applying an electric current through the inner wire. Coercive fields and remanent magnetization as functions of the circular field strength are explored. By means of a simple analytical model and OOMMF simulations, once the current is turned on, two key results have been found: (i) A manipulable axial demagnetization, that is, a magnetization transition from the quasi uniform alignment to a flux closure circular configuration when the circular field strength is above a critical field; and (ii) a quadratic reduction of the coercivity on the circular field strength...