Magneto-optic studies of ZnO doped with transition metals Co, Mn, V and Ti indicate a significant magnetic circular dichroism (MCD) at the ZnO band edge at room temperature, together with an associated dispersive Faraday rotation. Similar spectra occur for each dopant which implies that the ferromagnetism is an intrinsic property of the bulk ZnO lattice. At 10 K additional paramagnetic contributions to the MCD are observed, but above about 150K, the magnitude of the MCD signal is dominated by the ferromagnetism and is almost temperature independent. The MCD at the ZnO band edge shows room temperature hysteretic behaviour. DOI: PACS numbers: 75.50 Pp, 75.50 Pp, The search for spintronic materials that combine semiconducting and ferromagnetic properties, dilute magnetic semiconductors (DMS), is currently the most topical field in magnetism. The compounds based on the wide-gap (3.4 eV) semiconductor ZnO are especially exciting because they exhibit ferromagnetism at room temperature [1][2][3][4][5][6], in contrast to the GaMnAs-based materials for which the highest reported Curie temperatures, T c , are still well below 300 K.Despite the growing body of evidence in favour of room temperature magnetic hysteresis in doped ZnO, the nature of the ferromagnetism is hotly contested. The original interest in ZnO was prompted by the prediction that the hole exchange mechanism found in GaMnAs would produce Curie temperatures above 300 K [7]. However, it is now known that the doping is normally n-type, for which the exchange is smaller [8]. Furthermore, the measured moments are often much smaller than the theoretical values, which suggests that the magnetism might be due to an impurity phase [9,10]. It is therefore highly important to carry out careful experimental studies that can elucidate the microscopic origin of the magnetism.In this Letter we present a detailed study of the magnetooptical (M-O) properties of ferromagnetic ZnO, together with other experimental details. A measurement of the magnetic circular dichroism (MCD) at photon energy E gives the difference in absorption for left and right circularly polarised light at that same energy. Hence it provides a clear indication of the extent to which the states involved in the transition at that particular energy are influenced by the magnetism. We concentrate here on the spectral region close to the band edge at ~3.4 eV, since this characterizes the intrinsic behaviour of the ZnO lattice. The results show that the ferromagnetism at 300K is intimately connected with the band electrons of ZnO and that the carriers are polarised. Furthermore, since ZnO is transparent in the blue/UV, the large Faraday rotations that we observe around 3 eV are potentially useful for applications in M-O processing.The Zn 1−x M x O samples studied here (M = transition metal) were grown as thin films by pulsed laser deposition (PLD) on sapphire (0001) substrates. Co, Mn, V and Ti were used as the dopants with concentrations up to 5%. An undoped ZnO film was also grown for reference. SQ...

The realization of semiconductors that are ferromagnetic above room temperature will potentially lead to a new generation of spintronic devices with revolutionary electrical and optical properties. Transition temperatures in dopedZnO are high but, particularly for Mn doping, the reported moments have been small. We show that by careful control of both oxygen deficiency and aluminium doping the ferromagnetic moments measured at room temperature in n-type ZnMnO and ZnCoO are close to the ideal values of 5µ B and 3µ B respectively. Furthermore a clear correlation between the magnetisation per transition metal ion and the ratio of the number of carriers to the number of transition metal donors was established as is expected for carrier induced ferromagnetism for both the Mn and Co doped films. The dependence of the magnetisation oncarrier density is similar to that predicted for the transition temperature for a dilute magnetic semiconductor in which the exchange between the transition metal ions is through the free carriers.

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We propose a solution to improve gain-clamped EDFA stabilization time by inserting in the conventional laser loop configuration an extra SOA. Experimental results demonstrate stabilization time as short as 0.2µs in a purposely-considered critical situation.