Effect of sink layer thickness on damping in CoMnGe (5 nm) / Ag (6 nm) / NiFe (x nm) spin valves
Valkass, Robert Alexander James; Shelford, Leigh R; Durrant, Chris J; et al.Figueroa, Adriana; Baker, Alex A; Shafer, Padraic; Arenholz, Elke; Childress, Jeffrey R; Katine, Jordan A; van der Laan, Gerrit; Hicken, Robert J
Date: 4 April 2016
University of Exeter
In spin valve structures the damping of a ferromagnetic layer driven at resonance can be modified by the transfer of spin angular momentum into a ‘sink’ ferromagnetic layer. This effect, known as spin pumping, is interface dominated and expected to increase with increasing sink layer thickness up to a saturation absorption depth, ...
In spin valve structures the damping of a ferromagnetic layer driven at resonance can be modified by the transfer of spin angular momentum into a ‘sink’ ferromagnetic layer. This effect, known as spin pumping, is interface dominated and expected to increase with increasing sink layer thickness up to a saturation absorption depth, previously reported to be 1.2 nm regardless of the sink layer’s composition . Using vector network analyser ferromagnetic resonance (VNA-FMR), we have studied the variation in damping as a function of sink layer thickness in a series of CoMnGe (5 nm) / Ag (6 nm) / NiFe (x nm) spin valves. These measurements show only small variations in the CoMnGe Gilbert damping parameter for x ≤ 1.8 nm, although damping is observed to increase at x = 0.3 and 0.6 nm. Element-resolved x-ray detected ferromagnetic resonance (XFMR)  measurements confirm spin transfer torque due to spin pumping as the origin of the damping for x = 1.5 and 1.8 nm, with both thicknesses having the same effective spin mixing conductance, supporting the findings of Ghosh et al . For thicker sink layers the source and sink FMR fields are seen to coincide, hampering the identification of spin pumping.  A Ghosh, et al. Physical Review Letters 109, 127202 (2012)  M Marcham, et al. Physical Review B 87, 180403 (2013)
Physics and Astronomy
College of Engineering, Mathematics and Physical Sciences
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