Mechanical Strain Manipulation of Exchange Bias Field and Spin Dynamics in FeCo/IrMn Multilayers Grown on Flexible Substrates.

As a key effect in spintronic devices, exchange bias has attracted tremendous attention. Various approaches have been attempted for optimizing this effect, among which the application of strain in flexible exchange-biased systems is promising but little significant improvement has been reported. Here, we demonstrate encouraging progress in this field. With a pure mechanical compressive strain of -6.26‰ applied to the flexible polyimide (PI) substrate, distinct enhancement of ~900% in the bias field (from 20 Oe to 200 Oe) is achieved for the exchange-biased (FeCo/IrMn)3/Ta multilayers grown on top of a flexible polyimide substrate, accompanied by a notable decrease in the Gilbert damping parameter from 0.02 to 0.008, signifying an improved exchange bias effect as well as a potentially reduced switching current density. The underlying mechanism is investigated by a systematic ferromagnetic resonance study, suggesting that the angle between the unidirectional and uniaxial magnetic easy axes plays an important role, which may be controlled by adjusting the layer number. This work offers an efficient strategy for tuning the exchange bias effect via applying appropriate mechanical strain on a multi-periodic exchange bias multilayered system, opening up an avenue for tailoring the magnetic properties of flexible spintronic devices.