Size-dependent magnetic properties of 100–500 nm diameter IrMn/NiFe disks made by a two-step deposition process

Abstract

A two-step etching and deposition process is presented for making nanoscale exchange-biased NiFe/IrMn disks, and their magnetic properties are described as a function of diameter and thickness. The exchange bias in nanodots with diameters of 100–500 nm was reduced and the coercivity enhanced compared to the continuous film. Etching of the NiFe film prior to depositing the IrMn lowered the exchange bias; and the exchange bias also decreased as dot diameter decreased. The results are interpreted in terms of the relation between dot size and the antiferromagnetic domain size in the IrMn. The two-step process will be useful in introducing exchange bias at local regions of a ferromagnetic film.

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

“…Because of significant training effects [22] as seen in NiFe/IrMn dots [20], the samples are field cooled from 550 K after each hysteresis measurement. The Object Oriented MicroMagnetic Framework (OOMMF) package [23] is used to model the switching behavior as a function of the IrMn stripe width and spacing.…”

“…The patterned samples are prepared using a modification of a process presented earlier [20]. Ta ð5 nmÞ=Ni 80 Fe 20 (10 nm) is deposited on top of a Si wafer using triode sputtering at 2 × 10 −8 Torr base pressure and 1 m Torr Ar pressure with a growth rate of 0.132 nm s −1 .…”

“…However, contamination of the AF or FM interface between the two separate deposition steps can degrade the exchange bias. To improve the interface coupling, we previously presented a hybrid method [20] in which a predeposited NiFe film was etched back by 1 nm to remove any surface oxides, followed by growth of 1 nm additional NiFe then an IrMn film. This produced exchange bias similar to that found in NiFe/IrMn grown without a vacuum break.…”

Magnetization reversal in ferromagnetic wires patterned with antiferromagnetic gratings

“…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.…”