Abstract. Room-temperature ferromagnetism is observed in (110) oriented ZnO films containing 5 at % of Sc, Ti, V, Fe, Co or Ni, but not Cr, Mn or Cu ions. There are large moments, 1.9 and 0.5µ B /atom for Co-and Ti-substituted oxides, respectively. Scsubstituted ZnO shows also a moment of 0.3 µ B /Sc. Magnetization is very anisotropic, with variations of up to a factor three depending on the orientation of the applied field relative to the R-cut sapphire substrates. Results are interpreted in terms of a spin-split donor impurity band model, which can account for ferromagnetism in insulating or conducting high-k oxides with concentrations of magnetic ions that lie far below the percolation threshold. The variation of the ferromagnetism with oxygen pressure used during film growth is evidence of a link between ferromagnetism and defect concentration.PACS Numbers: 75.50.Pp; 75.30.Hx;75.30.Gw;75.70 [2][3][4][5][6] or another transition element [7][8][9][10]. The results are sensitive to the form of the sample and preparation method. Other studies found lower magnetic ordering temperatures [11][12][13][14], or no ferromagnetism at all above 3 K for any 3d dopant [15]. In the absence of an exchange mechanism which could account for a high Curie temperature at doping levels far below the percolation threshold, these reports have been received with skepticism, and the belief that the ferromagnetism must somehow be associated with clustering or incipient formation of secondary phases. But there is spectroscopic evidence that divalent cobalt does indeed substitute on the tetrahedral sites of the wurtzite structure [1,11,17], with a wide solid solubility range [15]. A search by Rode et al [4] revealed no evidence for phase segregation in Co-doped ZnO films.Nevertheless, until a clear connection between the magnetic properties and electronic structure can be shown, doubts that doped zinc oxide is truly a magnetic semiconductor will persist.We recently proposed a model for high-temperature ferromagnetism in dilute n-type

Articles you may be interested inEffect of metal-ion doping on the optical properties of nanocrystalline ZnO thin films

Conical refraction was produced by a transparent biaxial crystal of KGd(WO 4 ) 2 illuminated by a laser beam. The ring patterns at different distances from the crystal were magnified and projected onto a screen, giving rings whose diameter was 265 mm. Comparison with theory revealed all predicted geometrical and diffraction features: close to the crystal, there are two bright rings of internal conical refraction, separated by the Poggendorff dark ring; secondary diffraction rings decorate the inner bright ring; as the distance from the crystal increases, the inner bright ring condenses onto an axial spot surrounded by diffraction rings. The scales of these features were measured and agreed well with paraxial theory; this involves a single dimensionless parameter ρ 0 , defined as the radius of the rings emerging from the crystal divided by the width of the incident beam. The different features emerge clearly in the asymptotic limit ρ 0 ≫1; in these experiments, ρ 0 =60.

Articles you may be interested inEffect of structural and magnetic exchange coupling on the electronic transport of NdNiO3 films intercalated with La0.7Sr0.3MnO3 thin layersThe magnetic, transport, and structural properties of (La 0.1 Sr 0.3 ͒MnO 3 films deposited on MgO ͑001͒ are reported as a function of thickness and substrate temperature. The substrate temperature is fundamental in determining the structural properties and a deviation from the optimum temperature ͑680°C͒ leads to grain boundaries and an imperfect ͑001͒ texture. Films with different thicknesses were deposited at the optimum deposition temperature. Magnetization and resistivity measurements on these films are interpreted in terms of magnetic and electric ''dead'' layers. The electric dead layer is an insulating layer approximately 4 nm thick while the magnetic dead layer is a region of weakly coupled noncollinear spins approximately 10 nm thick at each interface.

For laser ablation plumes that are significantly ionized, Langmuir probes have proved to be a useful tool for measuring the plume shape, ion energy distribution, and electron temperature. Typically in laser ablation plasmas the flow velocity is supersonic, which complicates the interpretation of the current-voltage probe characteristic. In this paper we describe some recent developments on the application of Langmuir probes for laser ablation plume diagnosis. We have investigated the behavior of the probe when it is orientated perpendicular, and parallel, to the plasma flow, and show how an analytical model developed for plasma immersion ion implantation, can quantitatively describe the variation of the ion current with probe bias for the case when the plasma flow is along the probe surface. The ion signal recorded by a probe in the parallel position is proportional to the ion density and the square root of the bias voltage. It is shown that the current varies as m i −1/2 so that by comparing the ion signals from the parallel and perpendicular positions it is possible to estimate the mass of the ions detected. We have also determined the temporal variation of electron temperature. A planar probe oriented parallel to the plasma flow, where the ion current due to the plasma flow is eliminated, gives a more reliable measurement of T e ͑Ͻ0.6 eV͒. The measured T e is consistent with the measured ion current, which is dependent on T e when the time taken for an element of plasma to traverse the probe is longer than the time taken for the matrix ion sheath extraction phase.