1292 Fig. 2 a XRD patterns of ZnFe2 and b ZnFe2O4 nanowire arrays within AAO templates. The inset in Fig. 2b is the XRD patten of ZnFe2O4 powders for comparison. c Schematic illustration of the crystal growth process for ZnFe2O4 nanowire arrays Fig. 3 Magnetic hysteresis loops of the ZnFe2O4 nanowires within AAO measured with the applied ﬁeld parallel and perpendicular to the axis of the nanowires at (a) 300 K and (b) 80 K by SQUID. The magniﬁed view of the magnetic hysteresis loops is shown in right bottom insets of Fig. 3a and b, respectively. RT magnetic hysteresis loops of ZnFe2 nanowire arrays within AAO templates measured using VSM are shown in left top inset of Fig. 3a 123 Nanoscale Res Lett (2010) 5:1289–1294 magnetization values. In our experiment, when ZnFe2 alloy nanowires were post-oxidation annealed, defects and the disorder of cation redistribution on A- and B- sites may occur, which can induce the magnetization for ZnFe2O4 nanowire arrays in our case. For the spinel ferrite, the easy axis of magnetization is [100], and the hard one is [111]. The axis [110] is between them having the angle (h) of 45 with the [100] and [111] directions, respectively. The total anisotropy is determined by the magnetostatic energy and the magnetocrystalline anisotropy energy. As the nanowires are oriented in poly- crystals with high aspect ratio of 125, the easy magneti- zation direction determined by magnetostatic energy is along the axis of the nanowires. It can be seen from Fig. 4, the anger of a is not ﬁxed but changed from 0 to 360 in xy plane. So we presumed that the distribution of [100] may be like a conical axis shown in Fig. 4. When the applied ﬁeld H is parallel to the nanowire axis ([110] direction), the magnetic moment components in xy plane cancel out each other, while the magnetic moment components in [110] direction are summed up. Owing to the high aspect ratio of the nanowires, it is concluded from earlier analyses that the easy magnetization axis of the nanowires is along the axis direction. We further perform the PL spectroscopy to explore the optical properties of the ZnFe2O4 nanowires. Figure 5 illustrates the RT PL spectra of ZnFe2O4 nanowire arrays within AAO templates. The broadband visible emission band is observed in the entire PL spectrum, which can be ﬁtted by two main emission bands: one is in the blue light region, and the other is in the violet light one. The blue emission around 468 nm can be assigned to intrinsic defects, particularly interstitial zinc defects [36]. And the same violet emission around 412 nm was also observed in excessive 50% Fe doped ZnO nanostructure where this luminescence was considered to be signiﬁcantly contrib- uted by the ZnFe2O4 phase [37], which is corresponding to Fig. 4 Schematic illustration of easy magnetization axis and distri- bution of [100] direction for preferred oriented ZnFe2O4 nanowire arrays