Thermomagnetic writing in GdIG

A model for thermomagnetic writing in a GdlG platelet held at its compensation temperature is developed and confirming experimental data are presented. It is postulated that magnetization reversal occurs by domain nucleation and expansion. The relationship between the applied field
H
, the final bit diameter
D
, and the absorbed energy
P\tau
is shown to be
H = K^{-1}[(D^{2}\rhoc\omega)/(\alphaP\tau)][(1/2)E_{c}+ \sigma_{\omega}/D]
where
K = 0.112
is a normalization constant, ρ the density,
c
the specific heat, ω the sample thickness, α a constant relating the magnetization and the temperature, E
c
the domain-wall coercive pressure, and σ
ω
is the wall energy per unit area. Domains with
D < D_{c} = 2 \sigma_{\omega}/E_{c}
are unstable and collapse when the sample returns to the compensation temperature. Measurements are reported of the dependence of
D
on
H
for several values of P
tau
for a 13-μm thick platelet of aluminum doped GdIG. The quantitative agreement between theory and experiment is good. Observations of domain switching during the heat pulse application confirm all the major features of the model. The results show that in thick and low coercive force platelets, an excessive amount of power is required to write at moderate fields and the bit density is limited by the instability for
D < D_{c}
. Typical values are
P = 100
mW,
\tau = 1\mu
s,
H = 100
Oe, and
D_{c} = 20\mu
m. In thin and high coercive force films it should be possible to write 10-μm size bits with a field of < 100 Oe and a power level of 10 mW absorbed in 1 μs