IEEE Magnetics Society
Santa Clara Valley Chapter


Tuesday, May 24th, 2016

Western Digital, 1710 Automation Parkway, San Jose, CA 95131
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Cookies, Conversation & Pizza at 6:30 P.M.
Presentation at
7:00 P.M.



An Array of Ferromagnetic Nano-Islands Non-Destructively Patterned Via a Local Phase Transformation by Low-Energy Proton Irradiation

Jongill Hong, Yonsei University, Seoul, Korea




Low-energy proton irradiation was applied to pattern an array of metallic, ferromagnetic nano-islands through the local phase transformation of an oxidic, paramagnetic phase in a complex superlattice composed of repetitions of an oxidic and metallic layer. The irradiation inflicted minimal damage on the structure, resulting in the absence of unwanted defects and side effects [1]. This non-destructive pattern transfer was clearly confirmed by the contrast between irradiated and unirradiated regions in electrical, chemical, and magnetic images. Simulation based on the magnetic properties suggests that this low-energy proton irradiation can non-destructively pattern an array of ferromagnetic islands with 8.2 nm in diameter and 7.4 nm in spacing between islands, which means it can achieve an areal density of ~3 Tb/in2 with a thermal stability of over 80 kBT. Such an array is strong enough to overcome the so-called superparamagnetism limit in magnetic recording. The attributes demonstrated here corroborate that proton irradiation can be applied to design and pattern devices on a nanometer scale not only for magnetic but also for electric and optical materials systems in all such systems in which a local phase transformation is available.

[1] Kim, S.; Lee, S.; Ko, J.; Son, J.; Kim, M.; Kang, S.; Hong, Jongill*. Nanoscale Patterning of Complex Magnetic Nanostructures by Reduction with Low-Energy Protons. Nat. Nanotech. 2012, 7, 567-571.

[2] Kim, S.; Lee, S. and Jongill Hong*. An array of ferromagnetic nanoislands nondestructively patterned via a local phase transformation by low-energy proton irradiation. ACS Nano, 2014, 8, 4698-4704.






Jongill Hong is a Professor in Materials Science and Engineering at Yonsei University. He is doing research and development of spintronic materials and devices such as advanced spin switching devices utilizing spin-orbit torque and spin-transfer torque. He is also studying and developing spintronic devices, such as MTJ-based junctions, spin transistors, and graphene spintronics. Unique 3-D patterning for perpendicular patterned magnetic media for over 3 Tb/in2 is also his focus. He received his Ph.D. degree in Materials Science and Engineering from Stanford University in 1999.

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