Micromagnetic simulation of the magnetic switching behaviour of mesoscopic and nanoscopic structures
J. Fidler, T. Schrefl, V. D. Tsiantos, W. Scholz, D. Suess
J. COMPUTATIONAL PHYSICS EMRS-Conference 2001, PAPER Reference:A-VI.1
Magnetic switching of small particles, thins film elements and
nano-wires becomes increasingly important in magnetic storage and
magneto electronic devices. The magnetisation reversal processes are
studied using a three dimensional hybrid finite element/boundary
element micromagnetic model. Transient magnetization states during
switching are investigated numerically in thin Ni80Fe20
and Co nano-elements of square (100 x 100 nm2 ),
rectangular (100 x 300 nm2 ) and
circular (100 nm diameter) shapes with a thickness of 20 nm.
Switching dynamics are calculated for external fields applied
instantaneously and for rotational fields with field strengths in the
order of the static critical field
(Hext=0.02-0.32 Js/mu0).
Reversal in the unidirectional field proceeds by the nucleation and
propagation of end domains toward the centre of the particle. It is
found that the switching time strongly depends on the Gilbert damping parameter
alpha. Small values of alpha (<=0.1) lead to shorter
switching times at small field strength values, whereas for
Hext=0.6-1.0 Js/mu0 minimum switching times
occur for large damping value alpha=1.0.
Materials with uniaxial magneto-crystalline anisotropy, such as Co,
require larger field strengths, but exhibit shorter switching times.
Reversal in rotational fields involves inhomogeneous rotation of the
end domains toward the rotational field direction. Depending on the
damping parameter fast switching times (<=0.1 ns)
are obtained by increasing the field strength to
Hext=0.5 Js/mu0.
Taking into account thermal fluctuations the reversal mechanisms of
Co nano-wires were studied, and values for the activation volume and
for the domain wall velocity were derived.
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Feb. 13, 2001