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

Abstract

Domain wall propagation has been measured in continuous, weakly disordered, quasi-two-dimensional, Isinglike 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.

Reconfigurable magnetic domain wall pinning using vortex-generated magnetic fields

“…Less geometrically severe approaches to pinning include the use of electric fields 9 or local modifications to anisotropy [10][11][12][13][14][15] . Alternatively, one can use stray magnetic fields generated by ferromagnetic elements to pin domain walls moving in a neighboring strip or film [16][17][18][19] . This approach offers the attractive property of (nonvolatile) reconfigurability since the magnetic state of the pinning-inducing element may be switched, meaning that the pinning strength can be changed, thus enabling the development of controllable gates for DW motion 15 .…”

Tunable exchange bias-like effect in patterned hard-soft two-dimensional lateral composites with perpendicular magnetic anisotropy

“…17 This lateral approach can be taken a step further with the design of 2D lateral structures on continuous magnetic films: ordered 2D arrays of hard magnetic elements (Co and CoPt) coupled to soft permalloy films have been used to modify its magnetization reversal process through magnetostatic interactions; 18,19 also, out-of-plane exchange bias effects have been demonstrated in arrays of CoPt platelets coupled to a continuous CoPt film with strong perpendicular magnetic anisotropy. 20 In this framework, magnetic materials with weak perpendicular magnetic anisotropy (PMA), 21 such as thin films of amorphous NdCo alloys, present several interesting features for the design of 2D hard/soft lateral composites since their magnetic behavior is strongly thickness dependent due to the interplay between out-of-plane anisotropy and magnetostatic energy. 22 Below a critical thickness, they show a soft magnetic behavior with in-plane magnetization; however, above this critical thickness, weak stripe domains are nucleated in the magnetic film, which implies a significant hardening of in-plane hysteresis loops and the onset of the so-called rotatable anisotropy.…”

Controlled manipulation of domain walls in ultra-thin CoFeB nanodevices

“…Engineering of pinning sites to match stringent criteria is a common requirement in emerging DW devices [16]. Possible methods have been studied in both in-plane [17,12] and perpendicular materials [18,19].…”