Roger Ward

Abstract:

Well-aligned nanoneedles are found to form in a FeGaAs (001) epitaxial thin film when irradiated with a Ga+ ion beam normal to the sample surface at an ion dose of 3× 1017 cm2 in a focused ion beam. These nanoneedles, with their axes perpendicular to the original sample surface, are composed of GaAs nanorods with Fe nanoislands situated at the top. The GaAs nanorods, formed from the GaAs substrate, are crystalline and in the same crystal orientation as the GaAs substrate. The crystalline nature of the Fe thin film is disrupted by the ion sputtering, becoming nanocrystalline Fe islands. It is the thin Fe layer that is responsible for the formation of the nanoneedles. The ion sputtering of the Fe layer roughens the sample surface due to the uneven sputtering rate of the Fe layer. The removal of the Fe layer exposes the substrate to the incident ions, which then sputter the substrate leading to the formation of the nanoneedles. © 2006 American Institute of Physics.

Abstract:

Equiatomic PtMn layers have been grown epitaxially on Si (001), with the face-centered tetragonal L10-ordered antiferromagnetic phase forming without post-growth magnetic field annealing. The thickness dependence of the exchange anisotropy field and coercivity of the NiFe ferromagnetic layer in the epitaxial PtMn/NiFe exchange-coupled bilayers showed the critical thickness of the PtMn to be 10 nm. The exchange biasing properties are stabilised above a PtMn thickness of 15 nm which is much lower than that for polycrystalline PtMn-based exchange-biased systems. The highest value of exchange-bias is observed for a NiFe ferromagnetic layer thickness of 6 nm. The temperature dependence of the magnetic properties in the range 50-400 K shows that H ex and Hc increase monotonically in a quasi-linear manner as temperature decreases. Non-saturation of the in-plane magnetisation component of the PtMn, due to the Néel axis lying normal to the interface, is suggested to be responsible for the temperature dependence. © 2005 Elsevier B.V. All rights reserved.