35 research outputs found
Effects of Nanodots Shape and Lattice Constants on the Spin Wave Dynamics of Patterned Permalloy Dots
Micromagnetic simulations studies on Permalloy (Ni80Fe20) nanodot with
different shape and edge-to-edge separation (s) down to 25nm arranged in square
lattice are reported. We observe the significant variation of spin-wave (SW)
dynamics of nanodots of different shapes (triangular, diamond and hexagon) and
of fixed dot diameter 100nm with varying s. Modes for single dot are
transformed in an array into multiple quantized, edge and centre modes for
different shapes and edge-to-edge separations, with different spin wave
frequencies and peak intensities. Specifically, in the triangular dot sample, a
broad range of mode frequencies is observed with highest SW frequency 14.7 GHz.
For separation less than 100nm, the SW frequencies undergoes significant
modification due to the varying nature of the magnetostatic and dipolar
interaction in the array while for separation above 100nm, the SW frequency
mostly remain constant. The power profiles confirm the nature of the observed
modes. The spatial profiles of magnetostatic field are determined by a
combination of internal magnetic-field profiles within the nanodots and the
magnetostatic fields within the lattice. The inter-dots interaction of
magnetostatic field shows dipolar and quadrupole contributions for all the
shapes. Interestingly, vortex states with shifted core and polarity are
observed in the array for all the shapes at Hbias = 0. Our results provide
important understanding about the tunability of SW spectra in the array of
triangular, diamond and hexagon shaped nanoelements.Comment: 13 pages, 8 figure
Driven weak to strong pinning crossover in partially nanopatterned 2H-NbSe2 single crystal
Investigations into the heterogeneous pinning properties of the vortex state
created by partially nano-patterning single crystals of 2H-NbSe2 reveal an
atypical magnetization response which is significantly drive dependent.
Analysis of the magnetization response shows non-monotonic behavior of the
magnetization relaxation rate with varying magnetic field sweep rate. With all
the patterned pinning centers saturated with vortices, we find that the pinning
force experienced by the vortices continues to increase with increasing drive.
Our studies reveal an unconventional dynamic weak to strong pinning crossover
where the flow of the vortex state appears to be hindered or jammed as it is
driven harder through the interstitial voids in the patterned pinning lattice.Comment: 15 pages with 5 figure
Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars
We have studied microwave emission from a current-perpendicular-to-plane
pseudo spin valve nanopillars with Heusler alloy Co2Fe(Ga0.5Ge0.5) electrodes.
Large emission amplitude exceeding 150 nV/Hz^0.5, partly owing to the large
magnetoresistance, and narrow generation linewidth below 10 MHz are observed.
We also find that the linewidth shows significant dependence on the applied
field magnitude and its angle within the film plane. A minimum in the linewidth
is observed when the slope of the frequency versus current becomes near zero.
This agrees with theoretical prediction that takes into account non-linear
phase noise as a source for linewidth broadening