He + ion irradiation study of continuous and patterned Co∕Pd multilayers

Abstract

Ion irradiation of continuous and patterned (Co∕Pd)n magnetic multilayer films has been studied as a mean to control magnetic anisotropy as well as to evaluate possible ion irradiation damage involved in ion-beam proximity lithography patterning. The coercivity of patterned medium was found to decrease from 11kOe for as patterned samples to 0.3kOe for samples with 800μC∕cm2 ion irradiation. Remnant squareness of the patterned samples remained essentially unchanged. As the number of bilayers increases in the sample, the effects vary, suggesting that several mechanisms of damage occur. Significantly, for typical irradiation doses used in ion-beam proximity lithography, no measurable alteration of magnetic properties was observed.

Reversal mechanisms in perpendicularly magnetized nanostructures

“…We believe a 50% reduction in anisotropy is a reasonable value, since the anisotropy has been shown to profoundly decrease and even undergo a sign change ͑i.e., becoming an in-plane one͒ with a small ion radiation dose. [18][19][20] In the case of uniform anisotropy, reversal is nucleated in a volume located at the center or interior of the nanodotsince the edges are stiffer due to the additional energy arising from the generation of magnetostatic edge charges-as shown in the upper inset of Fig. 3͑b͒.…”

Influence of ion irradiation on switching field and switching field distribution in arrays of Co/Pd-based bit pattern media

“…The structural results obtained on the reference multilayer are in good agreement with previous studies 3 and our findings on irradiated samples are coherent with past studies demonstrating that the major structural effect of irradiation with light He + ions is intermixing at interfaces without creation of crystalline orientation disorder. [10][11][12][13] Particularly, it has been clearly established that the initial crystallographic structure and microstructure ͑grain size͒ is maintained, no surface roughness resulting from sputtering and no ion implant into the magnetic layer are induced.…”

Magnetic nanostructures for advanced technologies: fabrication, metrology and challenges

“…As previously stated, the challenge to a subtractive method resides in mitigating the ion damage that can occur in the edge region and the possible re-deposition of the etched material along the edges. Many perpendicular multilayer systems, such as Co/Pd, are especially sensitive to ion induced damage and can transition from having a strong perpendicular anisotropy to an in-plane one with only a small amount of ion dose [69][70][71]. As a result, the magnetic anisotropy of the edge material can be modified significantly, resulting in a change in the reversal process of a nanostructure [68].…”