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

Abstract

The magnetic switching behavior in continuous NiFe films patterned with IrMn gratings is investigated experimentally and with micromagnetic simulations. The samples made by a two-step deposition process consist of a 10-nm-thick NiFe layer on which is placed 10-nm-thick IrMn stripes with width from 100 to 500 nm and period from 240 nm to 1 μm. Exchange bias is introduced by field cooling in directions parallel or perpendicular to the IrMn stripes. The samples display a two-step hysteresis loop for higher stripe width and period, as the pinned and unpinned regions of the NiFe reverse independently but a one-step loop for lower stripe periods. The transition between these regimes is reproduced by micromagnetic modeling.

Magnetization reversal in ferromagnetic wires patterned with antiferromagnetic gratings

“…This shows the evolution from a singlestep loop at w ¼ s ¼ 200 nm to a two-step loop for larger w and s. A similar transition was found previously in continuous NiFe films patterned with IrMn wires. 29 The micromagnetic configuration is uniform within the NiFe for the single-step loop for w ¼ s ¼ 200 nm at all fields including the switching field, À50 Oe. In several simulations with different random initial conditions, the magnetic configuration was oriented either all to the left or all to the right at À50 Oe, without any indication that the pinned and unpinned regions reversed at different fields to yield a non-uniform magnetization state.…”

“…26,27 For example, the magnetic properties of a continuous FM film partly covered with patterned AFM regions depend on the dimensions of the AFM and the strength of the exchange bias within the pinned regions, as shown in NiFe/FeMn 24 and NiFe/IrMn, 28 and Co films with O implantation showed local EB due to the formation of CoO in the implanted regions. 21 We showed earlier 29,30 that NiFe films patterned with IrMn stripes with a width of 100 to 500 nm and a period of 240 nm to 1 lm exhibited either single-step or two-step reversal depending on the IrMn dimensions. In this article, we extend this investigation to a structure consisting of an array of 200 nm wide NiFe stripes on which an orthogonal array of sub-500 nm wide IrMn stripes is patterned.…”

“…Alternatively, the FM and AFM layers may be patterned using two different lithography steps, but the processing compromises the quality of the FM/AFM interface which is critical for establishing exchange bias. Here, we use an additive method 29,30 in which a NiFe film is deposited and patterned, and then, a second lithography step is used to define the AFM-covered regions. A good quality FM/AFM interface is obtained by removing about 1 nm of the NiFe film by an ionbeam etch after the second lithography step and then depositing $1 nm NiFe followed by an IrMn layer.…”