Abstract:We investigated the dependence of the seed (Ta/Pt, Ta/Au) and capping (Pt/Ta, Au/Ta) layers on spin pumping effect in the ferromagnetic 3 nm thick Co thin film using ferromagnetic resonance spectroscopy. The data is fitted with Kittel's equation to evaluate damping constant and g-factor. A strong dependence of seed and capping layers on spin pumping has been discussed. The value of damping constant (α) is found to be relatively large i.e. 0.0326±0.0008 for the Ta(3)/Pt(3)/Co(3)/Pt(3)/Ta(3) (nm) multilayer structure, while it is 0.0104±0.0003 for Ta(3)/Co(3)/Ta(3) (nm). Increase in α is observed due to Pt layer that works as a good sink for spins due to high spin orbit coupling. In addition, we measured the effective spin conductance  g = 2.00 ± 0.08 × 10 18 m -2 for the tri-layer structure Pt(3)/Co(3)/Pt(3) (nm) as a result of the enhancement in α relative to its bulk value.We observed that the evaluated g-factor decreases as effective demagnetizing magnetic field increases in all the studied samples. The azimuthal dependence of magnetic resonance field and line width showed relatively high anisotropy in the tri-layer Ta(3)/Co(3)/Ta(3) (nm) structure.

Spintronics exploiting pure spin current in ferromagnetic (FM)/heavy metals (HM) is a subject of intense research. Topological insulators having spin momentum locked surface states exhibit high spin–orbit coupling and thus possess a huge potential to replace the HM like Pt, Ta, W, etc. In this context, the spin pumping phenomenon in Bi2Se3/CoFeB bilayers has been investigated. Bi2Se3 thin films are fabricated by electron beam evaporation method on Si (100) substrate. In order to confirm the topological nature of Bi2Se3, low temperature magnetotransport measurement on a 30 nm thick Bi2Se3 film which shows 10% magnetoresistance (MR) at 1.5 K has been performed. A linear increase in MR with applied magnetic field indicates the presence of spin momentum‐locked surface states. A voltage has been measured at room temperature to quantify the spin pumping which is generated via inverse spin Hall effect (ISHE). For the separation of spin rectification effects mainly produced by the FM CoFeB layer, in plane angular dependence of the dc voltage with respect to applied magnetic field has been measured. Our analysis reveals that spin pumping induced ISHE is the dominant contribution in the measured voltage.

Bi 2 Se 3 is a well-established topological insulator (TI) having spin momentum locked Dirac surface states at room temperature and predicted to exhibit high spin to charge conversion efficiency (SCCE) for spintronics applications. The SCCE in TIs is characterized by an inverse Edelstein effect length (λ IREE ). We report an λ IREE of ∼0.36 nm, which is the highest ever observed in Bi 2 Se 3 . Here, we performed spin pumping and inverse spin Hall effect (ISHE) in an electron beam-evaporated Bi 2 Se 3 / CoFeB bilayer. The Bi 2 Se 3 thickness dependence of λ IREE , perpendicular surface anisotropy (K S ), spin mixing conductance, and spin Hall angle confirmed that spin to charge conversion is due to spin momentum locked Dirac surface states. We propose that the role of surface states in SCCE can be understood by the evaluation of K S . The SCCE is found to be high when the value of K S is small.

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Dzyaloshinskii-Moriya interaction (DMI) manifesting in asymmetric layered ferromagnetic films gives rise to non-colinear spin structures stabilizing magnetization configurations with nontrivial topology. In this work magnetization reversal, magnetic domain alignment, and...