Spatially periodic domain wall pinning potentials: Asymmetric pinning and dipolar biasing

TL;DR

This study investigates how spatially periodic pinning potentials created by nanoplatelet arrays influence domain wall dynamics in magnetic layers, revealing effects similar to exchange bias and hysteresis modifications.

Contribution

It demonstrates that periodic pinning potentials induce an effective retardation field affecting domain wall motion, with dependence on array geometry and nanoplatelet magnetization orientation.

Findings

Effective retardation field depends on array geometry and magnetization orientation.

Hysteresis loops show properties akin to exchange bias systems.

Domain wall roughness varies with applied field polarity.

Abstract

Domain wall propagation has been measured in continuous, weakly disordered, quasi-two-dimensional, Ising-like magnetic layers that are subject to spatially periodic domain wall pinning potentials. The potentials are generated non-destructively using the stray magnetic field of ordered arrays of magnetically hard [Co/Pt]$_m$ nanoplatelets which are patterned above and are physically separated from the continuous magnetic layer. The effect of the periodic pinning potentials on thermally activated domain wall creep dynamics is shown to be equivalent, at first approximation, to that of a uniform, effective retardation field, $H_{ret}$, which acts against the applied field, $H$. We show that $H_{ret}$ depends not only on the array geometry but also on the relative orientation of $H$ and the magnetization of the nanoplatelets. A result of the latter dependence is that wall-mediated hysteresis loops obtained for a set nanoplatelet magnetization exhibit many properties that are normally associated with ferromagnet/antiferromagnet exchange bias systems. These include a switchable bias, coercivity enhancement and domain wall roughness that is dependent on the applied field polarity.