  We describe a quantum memory spectral preparation strategy that maximises
memory efficiency and bandwidth in materials such as 167 Er3+:Y2SiO5 in a high
field regime, where the hyperfine structure is resolved. We demonstrate the
method in 167 Er3+:Y2SiO5 by preparing spectrally isolated 18 dB-absorbing
features on a < 1 dB background. Using these features we create an atomic
frequency comb and show quantum storage of 200 ns pulses with 22% efficiency,
limited by the background absorption which arises from laser instability. We
describe the experimental improvements needed to reach the material limits:
O(1) s spin state storage, O(100) MHz bandwidth, and > 90% efficiency.
