Effect of stoichiometry and film thickness on the structural and magnetization dynamics behavior of Co2MnAl thin films cosputtered on Si(1 0 0)

Abstract

Obtaining low gilbert damping (α) and high spin polarization (P) in Heusler alloy thin films is one of the key requirements from the device application point of view in spintronics. Both α and P are correlated, closely related to the density of states (DOS) at the Fermi level and need to be controlled for engineered material. We investigated the effect of stoichiometry (different Co to Mn atomic percent ratios, viz. 2.21, 4.53, 5.43, and 9.19) and film-thickness {(t) in the range of 24–90 nm} on the structural and magnetization dynamics behavior in co-sputtered Co2MnAl thin films grown over Si(100) substrates. While the stoichiometric (∼50 at.% of Co) films with t ≥ 38 nm were found to exhibit B2 order with low α, the off-stoichiometric films (t ∼ 50 nm) were found to stabilize in partially ordered A2 phase and exhibited higher α. The change in structural ordering due to change in stoichiometry and film-thickness in polycrystalline Co2MnAl (CMA) thin films helped in tuning α in the range of (4.11 ± 0.06) × 10-3 – (11.95 ± 0.28) × 10-3. The minimum value of α ∼ (4.11 ± 0.06) × 10-3 was achieved for stoichiometric CMA (t = 70 nm) thin films which is close to the literature value of epitaxially grown L21 and B2 ordered CMA thin films. The study shows that we can tune and attain low damping in polycrystalline CMA Heusler thin films by controlling the stoichiometry.