Size dependent magnetization and high-vacuum annealing enhanced ferromagnetism in Zn(1-x)Co(x)O nanowires.
Diameter controllable ZnO nanowires have been fabricated by thermal evaporation (vapor transport) with various sizes of gold nanoparticles as catalysts. Diluted magnetic semiconductor (DMS) Zn(1-x)Co(x)O nanowires were then made by high energy Co ion implantation. The as-implanted and the argon-annealed Zn(1-x)Co(x)O nanowires displayed weak ferromagnetism while the high-vacuum annealed nanowires exhibited strong ferromagnetic ordering at room temperature. Size dependent behavior has been observed in the magnetic field and temperature dependences of magnetization. The shrinkage of the nanowire diameter reduced the spontaneous magnetization as well as the hysteresis loops. Field cooled and zero-field cooled magnetization and coercivity measurements were performed between 2 and 300 K to study the evolution of magnetism from the weak to the strong ferromagnetic states. In particular, superparamagnetic features were observed and shown to be intrinsic characteristics of the DMS Zn(1-x)Co(x)O nanowires. The room-temperature spontaneous magnetization of individual Zn(1-x)Co(x)O nanowires was also established by using magnetic force microscope measurements.
Jian
Wen-Bin
WB
Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan.
Chen
I-Jan
IJ
Liao
Tai-Ching
TC
Ou
Yi-Ching
YC
Nien
Cheng-Hsun
CH
Wu
Zhong-Yi
ZY
Chen
Fu-Rong
FR
Kai
Ji-Jung
JJ
Lin
Juhn-Jong
JJ