Magnetic Phase Transition in Ion-Irradiated Ultrathin CoN Films via Magneto-Optic Faraday Effect

Chiung-Wu Su; Yen-Chu Chang; Sheng-Chi Chang

doi:10.3390/ma6115247

Magnetic Phase Transition in Ion-Irradiated Ultrathin CoN Films via Magneto-Optic Faraday Effect

Materials (Basel). 2013 Nov 15;6(11):5247-5257. doi: 10.3390/ma6115247.

Authors

Chiung-Wu Su¹, Yen-Chu Chang², Sheng-Chi Chang³

Affiliations

¹ Department of Electrophysics, National Chiayi University, 300 Syuefu Rd., Chiayi 60004, Taiwan. cwsu@mail.ncyu.edu.tw.
² Department of Electrophysics, National Chiayi University, 300 Syuefu Rd., Chiayi 60004, Taiwan. y.c.chang0620@gmail.com.
³ Department of Electrophysics, National Chiayi University, 300 Syuefu Rd., Chiayi 60004, Taiwan. cloudmiss54@gmail.com.

Abstract

The magnetic properties of 1 nm thick in-plane anisotropic Co ultrathin film on ZnO(0001) were investigated through successive 500 eV nitrogen-ion sputtering. Magneto-optical Faraday effects were used to observe the evolution of the ion-irradiated sample in longitudinal and perpendicular magnetic fields. The ferromagnetic phase of the initial in-plane anisotropic fcc β-Co phase transformation to β-Co(N) phase was terminated at paramagnetic CoN_x phase. In-plane anisotropy with weak out-of-plane anisotropy of the Co/ZnO sample was initially observed in the as-grown condition. In the sputtering process, the N⁺ ions induced simultaneous sputtering and doping. An abrupt spin reorientation behavior from in-plane to out-of-plane was found under prolonged sputtering condition. The existence of perpendicular anisotropy measured from the out-of-plane Faraday effect may be attributed to the co-existence of residual β-Co and Co₄N exchange bonding force by the gradual depletion of Co-N thickness.

Keywords: Auger electron spectroscopy; cobalt nitrides; magnetic anisotropy; magnetic phase transformation; magneto-optic Faraday effects; zinc oxide.