Permalloy Nanostripes Research Articles

Observation of frequency band gaps in a one-dimensional nanostructured magnonic crystal

We report the experimental observation of band gaps in a synthetic nanostructured magnonic crystal composed of two different magnetic materials. The sample, in the form of a one-dimensional periodic array comprising alternating Permalloy and cobalt nanostripes, has been fabricated using advanced lithographic techniques. Dispersion relations of spin waves in the magnonic crystal have been mapped by Brillouin spectroscopy. The center frequency and width of the band gaps observed are tunable by an applied magnetic field. Dispersion relations calculated based on the finite element method accord with the measured data.

Resonant domain wall depinning induced by oscillating spin-polarized currents in thin ferromagnetic strips

The interaction between ac spin-polarized electrical currents and a domain wall initially trapped on a notch in a thin Permalloy nanostrip is investigated by micromagnetic modeling as well as a one-dimensional model that considers the wall as a rigid object. A systematic study of the depinning transition from the notch is carried out in the frequency domain for several static magnetic fields and ac's, both at zero and at room temperature. Due to the resonant amplification of the domain wall oscillations, both the depinning current and the static magnetic field can be significantly reduced with respect to the dc case, and even at room temperature the probability of the domain wall depinning abruptly changes in a narrow frequency range. These observations suggest a low-operation and highly selective mode for further spintronic devices based on domain walls. On the other hand, our analysis is also used to estimate the effective value of the nonadiabatic parameter by direct comparison with recent experiments.

High-frequency characterization of Permalloy nanosized strips using network analyzer ferromagnetic resonance

We report on the dynamic properties of Permalloy nanostrips at gagahertz frequencies. The thickness of the strips is 100nm, strip width is 300nm, strip spacing is 1μm, and length is 0.3–100μm; aspect ratios are 1:1, 1:2, 1:3, 1:5, 1:10, and 1:333. The dynamic behavior was studied by network analyzer ferromagnetic resonance (FMR) using Permalloy strips on a coplanar waveguide in flip-chip geometry. The FMR mode frequencies (fr) can be controlled by the aspect ratio as well as by the applied magnetic field (H). In longer strips (1:10 and 1:333), the excitation frequencies show a soft mode behavior (Heff=990Oe) when the field is along the hard axis. However, along the easy axis (along the strip length), fr increases with applied field. At a field of 3kOe, fr values are almost independent of aspect ratio along the easy axis except for the 1:1 strip. Along the hard axis, the frequencies are strongly dependent upon the aspect ratio. We also observed that the frequency linewidths of the strips are dependent on the aspect ratio.