Epitaxial growth of (0001) oriented ͓ZnO͑20 Å͒ /Co 0.7 Fe 0.3 ͑x Å͔͒ 25 multilayers (MLs) with nominal thickness x = 1, 2 and 5 has been prepared on ␣-Al 2 O 3 (0001) substrate by ion-beam sputtering. The magnetic properties over a temperature range of 6-350 K and structures probing by x-ray absorption spectroscopy (XAS) are reported. Above room-temperature ferromagnetism has been observed for x = 1 and x = 2 MLs, while superparamagnetic behavior dominates for x = 5 ML. The field-cooled magnetization-temperature M͑T͒ curves of x = 1 and x = 5 MLs can be fitted by a standard three-dimensional (3D) spin-wave and a Curie-Weiss model, respectively. For x = 2 ML, however, neither a 3D spin-wave nor a Curie-Weiss model, but a combination of the two fits the M-T curve. The XAS studies together with the magnetic measurements further reveal that x =1 sample behaves as a diluted magnetic semiconductor (DMS) ML, while x = 2 ML shows a mixed structure consisting of a minor component of DMS and a major component of CoFe clusters. A predominant clustering phase appears for x = 5 ML.

The effect of chromium doping on the defect-induced ferromagnetism of Zn1−xCrxO films was investigated in this study. X-ray diffraction and x-ray photoelectron results confirm Cr substitution at Zn sites in the ZnO host lattice. A parabolic dependence of the saturation magnetization on the stoichiometric variable x was observed. Photoluminescence and magnetic results indicate that magnetic moments in Zn1−xCrxO films stem from Zn vacancies on the film surface or at grain boundaries. As the variation in saturation magnetization is consistent with that in surface morphology, the ferromagnetism in Zn1−xCrxO films is sensitive to the morphological modification caused by Cr doping.

This article aims to investigate the Raman modes present in Mn-doped ZnO thin films that are deposited using the magnetron co-sputtering method. A broad band ranging from 500 to 590 cm −1 is present in the Raman spectra of heavily Mn-doped ZnO films. The multi-peak-fitting results show that this broad band may be composed of six peaks, and the peak at 528 cm −1 could be a characteristic mode of Mn 2 O 3 . The results of this study suggest that the origin of the Raman peaks in Mn-doped ZnO films may be due to three major types: structural disorder and morphological changes caused by the Mn dopant, Mn-related oxides and intrinsic host-lattice defects.

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Co/Cu͑111͒ multilayers, ͓Co͑17 Å͒/Cu͑8 ÅϽt Cu Ͻ14 Å͔͒ 30 , have been prepared on Co͑70 Å͒ buffer layers on Al 2 O 3 ͑0001͒ substrates by molecular beam epitaxy. From the longitudinal and transverse magnetoresistance ͑MR͒ measurements, it is observed that MRs consist of two components with a small anisotropic MR ͑Ͻ2%͒ component at low field sitting on top of the giant MR ͑up to 22%͒ component at higher field. The AMR effect strongly correlates with the abundance of hcp stacking of Co, which tends to decrease with the increasing of Cu spacer thickness. The AMR saturation fields ͑1-3 kOe͒ coincides with those of the magnetization. It is suggested that the observed AMR effect is due to scattering from the hcp-phase Co layers in the multilayers. This together with the large saturation field ͑30-40 kOe͒ obtained from the entire MR curves indicate that the observed GMR effect may result from the Co-Cu interfacial spin-dependent scattering.