Exchange anisotropy pinning of a standing spin wave mode

TL;DR

This study uses standing spin wave modes in a ferromagnetic/antiferromagnetic bilayer to probe interface pinning effects induced by exchange anisotropy, revealing how bias and temperature influence magnetic properties.

Contribution

It demonstrates that standing spin wave modes can serve as sensitive probes of exchange bias and interface anisotropy in ferromagnet/antiferromagnet systems, with insights into thermal effects.

Findings

Pinning of spin wave modes amplifies exchange bias signals.

Exchange bias correlates with changes in effective ferromagnetic thickness.

Cooling enhances pinning strength and alters interface magnetic order.

Abstract

Standing spin waves in a thin film are used as sensitive probes of interface pinning induced by an antiferromagnet through exchange anisotropy. Using coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin wave thickness mode in Ni(80)Fe(20)/Ir(25)Mn(75) exchange biased bilayers was studied for a range of IrMn thicknesses. We show that pinning of the standing mode can be used to amplify, relative to the fundamental resonance, frequency shifts associated with exchange bias. The shifts provide a unique `fingerprint' of the exchange bias and can be interpreted in terms of an effective ferromagnetic film thickness and ferromagnet/antiferromagnet interface anisotropy. Thermal effects are studied for ultra-thin antiferromagnetic Ir(25)Mn(75) thicknesses, and the onset of bias is correlated with changes in the pinning fields. The pinning strength magnitude is found to grow with cooling of the sample, while the effective ferromagnetic film thickness simultaneously decreases. These results suggest that exchange bias involves some deformation of magnetic order in the interface region.