Pseudo exchange bias due to rotational anisotropy

•Pseudo exchange bias can be found in square Py nanorings of different dimensions.•Pseudo exchange bias stems from unintentionally measuring minor loops.•New approach in explaining “real” exchange bias effect in coupled FM/AFM systems.•Theoretical base to explain other measurements of a rotational anisotropy.

Ferromagnetic nanostructure arrays with particle dimensions between 160 nm and 400 nm were created by electron-beam lithography. The permalloy structures consist of rectangular-shaped walls around a square open space. While measuring their magnetic properties using the Magneto-Optical Kerr Effect (MOKE), in some angular regions an exchange bias (EB) seemed to appear. This paper gives an overview of possible reasons for this “pseudo exchange bias” and shows experimentally and by means of micromagnetic simulations that this effect can be attributed to unintentionally measuring minor loops.