The zero-field QTM timescale (𝜏 𝑄𝑇𝑀 ) is in excellent agreement with that obtained from the zero-field ac data, and the field exponent (p) agrees well with that found for the axial SMM approaching the value expected for the single-phonon Direct process in the high-temperature limit of m = 4, and so we suggest this is a more-likely mechanism; however, we cannot rule out a contribution from the Raman-II mechanism.