Magnetization Reversal in Ferromagnetic Films Patterned with Antiferromagnetic Gratings of Various Sizes

F. Liu, C. A. Ross
2015 Physical Review Applied  
The magnetic switching behavior in continuous NiFe films patterned with IrMn gratings was investigated experimentally and with micromagnetic simulations. The samples, made by a two-step deposition process, consisted of a 10 nm thick NiFe layer on which was placed 10 nm thick IrMn stripes with width from 100 nm to 500 nm, and period from 240 nm to 1 μm. Exchange bias was introduced by field-cooling in directions parallel or perpendicular to the IrMn stripes. The samples displayed a two-step
more » ... resis loop for higher stripe width and period, as the pinned and unpinned regions of the NiFe reversed independently, but a one-step loop for lower stripe periods. The transition between these regimes was reproduced by micromagnetic modeling. Introduction: Exchange bias between a ferromagnet (FM) and an antiferromagnet (AFM) is important both in understanding magnetic exchange phenomena and for its applications in devices such as magnetic random access memories and hard disk read heads [1, 2] . Exchange bias leads to a unidirectional anisotropy, a shift of the hysteresis loop and often an increase in coercivity [3, 4] . Size effects in exchange-biased FM/AFM bilayers have been studied in several systems in which both layers are deposited sequentially then patterned to have the same lateral dimensions [5] [6] [7] [8] [9] . For example, in bilayer FM/AFM stripes consisting of ferromagnetic metals coupled to CoO, NiO, FeMn, or IrMn antiferromagnetic layers, exchange bias along the stripe axis decreased as the stripe width decreased [7, 11, 6, 12] but in another example of NiFe/NiO stripes the exchange bias increased with decreasing stripe width [13] . The magnetic behavior of locally exchange-biased thin films, in which the FM and AFM have different dimensions and the exchange-bias is limited to only part of the FM, differs qualitatively from that of patterned FM/AF bilayers. The reversal mechanism of the FM depends on the length scales of the pinned and unpinned regions and the strength of the exchange bias in the pinned regions. Locally exchange-biased structures
doi:10.1103/physrevapplied.4.054005 fatcat:xgwaob5whfh3riaxie5yy6mt7q