Coercivity of epitaxial magnetic garnet crystals

Epitaxial magnetic garnet films of Ga and Ca-Ge substituted YIG grown for bubble memory applications are thought to be the most perfect magnetic materials. However, in spite of their very low dislocation and surface defect densities (≤5 cm
²
) the coercivity H
c
is of the order of 10
^-1
Oe. This paper reviews the role of various mechanisms in determining static H
c
of stripe domains in epitaxial garnet crystals. Statistical fluctuations of material parameters, dislocations and localized surface defects are shown to give a negligible contribution to H
c
. The surface roughness of the free surface and stresses inside the transient layer at the substrate/epitaxy interface may cause H
c
from 0.1 up to some Oe. From the temperature dependence of H
c
a high density (10
¹⁴
to 10
¹⁶
/cm
³
) of micro-defects was deduced. Transmission electron microscopy revealed the existence of such precipitates responsible for the observed H
c
of device quality epitaxial garnets.