Spin-pumping investigations in as-deposited and 400 °C annealed Co60Fe20B20/Mo heterostructures

The spin-pumping behavior in the as-deposited and post-deposition annealed (at 400 °C) Co60Fe20B20/Molybdenum (CoFeB/Mo) heterostructures is investigated. It is found that while in both the as-deposited and annealed CoFeB/Mo heterostructures, Mo crystallizes in the form of mixed phases, i.e., body centered cubic ( bcc) and face centered cubic ( fcc), the dominance, however, changes from fcc to bcc on annealing. The ferromagnetic resonance measurements reveal that despite relatively low spin orbit coupling of Mo, the spin-pumping efficiency and magnetic properties in both the as-deposited as well as in the annealed heterostructures was comparable with those reported in similar CoFeB based heterostructures comprising of other nonmagnetic metals such as W and Ta. The spin efficiency parameters are, however, slightly better when the Mo film is predominantly in the fcc phase as compared to the case when the Mo film dominantly comprises of the bcc phase. The different spin-pumping efficiencies in the two different combinations of phases of Mo are attributed to the different band structures and the density of states in different phases of Mo, as confirmed by density functional theory calculations. The slight changes observed in the spin-pumping response are possibly attributed to the structural manifestations that result at the interface that the two phases of Mo share with CoFeB. Importantly, despite the weak spin–orbit interaction, the 4 d transition metal Mo could be a suitable choice of non-magnetic material for spin pumping when the thermal stability of different layers in the CoFeB based spintronic devices is of paramount concern.