  Here, we investigated the influence of grain formation on the magnetization
reversal of SmCo5/Co at low temperature. A set of SmCo5/Co bi-layer samples
were fabricated under identical conditions on MgO(100) and glass substrates
with a Cr underlayer. Analysis of each magnetic layer by an Atomic Force
Microscope (AFM) reveals that MgO(100) results small and uniform grain
formation of 23 nm in contrast to 57 nm on glass, and x-ray diffraction studies
show that the sample on MgO(100) has high crystallinity with SmCo5(11 0) phase.
At room temperature, both samples exhibit good hard magnetic properties with
coercivity (HC) of 13.2 kOe and 12.5 kOe, and energy products (BH)max of 14.5
MGOe and 5.3 MGOe for samples on MgO(100) and glass, respectively. Low
temperature hysteresis measurements show an exchange decoupling at low
temperatures for the sample on glass, and this is due to the formation of large
grains on glass that reduces the effective inter-grain exchange coupling
between phases.
