Abstract
Wurtzite-type ZnO tetrapod nanostructures were prepared by evaporating Zn metal under humid argon flow. After the fabrication, Mn was doped into ZnO nanostructures by diffusion at
600
°
C
. The average concentration of Mn was determined to be
8.4
mol
%
by x-ray fluorescence. X-ray diffraction patterns obtained from the doped and undoped samples are almost the same. High-resolution transmission electron microscopy observations reveal the existence of surface layers. Magnetic measurements show that the sample has a very large coercivity
H
C
=
5500
Oe
at
5.5
K
and a Curie temperature
T
C
=
43
K
, which may suggest that ferrimagnetic
(
Zn
,
Mn
)
Mn
2
O
4
exists at the surface. Exchange bias is clearly observed below
22
K
. Exchange bias is attributed to the exchange interaction between ferrimagnetic
(
Zn
,
Mn
)
Mn
2
O
4
and spin-glass-like (or antiferromagnetic) phase in manganese oxides.