Control of chiral magnetic textures in B20 transition metal germanide epilayers

In order to realise the technological potential of skyrmion-based spintronics, thin film materials with high ordering temperatures and controlled skyrmion size are needed. The canonical B20 FeGe magnetically orders below about 280 K and and has a skyrmion size of ~90 nm, set by the pitch of the spin helix in the helimagnetic ground state. It is known that substituting Mn onto the Fe site (reducing the electron density) causes a change in sign of the DMI at which a divergence of the helix pitch takes place, but doping on the Co site is unexplored. In our previous beamtime we measured two Fe(1-x)Co(x)Ge epilayers, with x = 0.3 and 0.6 and saw tantalising hints of another unexpected divergence at x = 0.6. Here we propose an experiment where we will look more closely in this composition range in order to confirm the presence of this divergence and map its features more clearly.