Dielectric Relaxation in Nanopillar NiFe-Silicon Structures in High Magnetic Fields

Abstract

We explore the dielectric relaxation properties of NiFe nanowires in a nanoporous silicon template. Dielectric data of the NiFe-silicon structure show a strong relaxation resonance near 30K. This system shows Arrhenius type of behavior in the temperature dependence of dissipation peaks vs. frequency. We report magnetic field dependence of dipolar relaxation rate and the appearance of structure in the dielectric spectrum related to multiple relaxation rates. A magnetic field affects both the exponential prefactor in the Arrhenius formula and the activation energy. From this field dependence we derive a simple exponential field dependence for the prefactor and linear field approximation for the activation energy which describes the data. We find a significant angular dependence of the dielectric relaxation spectrum for regular silicon and nanostructured silicon vs. magnetic field direction, and describe a simple sum-rule that describes this dependence. We find that although similar behaviour is observed in both template and nanostructured materials, the NiFe-silicon shows a more complex, magnetic field dependent relaxation spectrum.