Controlling magnetic configuration in the soft/hard bilayers probed by PNR*

Hard-soft magnetic composites have played an important role in the data storage and permanent magnetic technology [1]. Understanding the full range of interactions within hard-soft coupled systems is critical to maximizing their benefit in composite applications [2]. Here, we present polarized neutron reflectometry (PNR) to experimentally study magnetic configurations in hard/soft bilayers. By designing saturation magnetization of hard () and soft () magnets and the soft layer thickness (), the magnetic interactions, and resulting configuration, is systematically varied. When less than the critical exchange length (, the magnetic moments of soft layer are rigidly coupled to magnetic hard layer. While for , magnetic moments in the soft layer becomes relaxed in plane. This relaxation can be slowly released in thicker magnetic soft layers with lower and higher. These results are then supported with micromagnetic simulation.
[1] Y. Sonobe et al., IEEE Trans. Magn 37, 1667 (2001)
[2] D. A. Gilbert et al., Sci. Rep. 6, 32842 (2016)