| 1. |
- Pappas, S. D., et al.
(författare)
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Layering and temperature-dependent magnetization and anisotropy of naturally produced Ni/NiO multilayers
- 2012
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 112:5, s. 053918-
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Tidskriftsartikel (refereegranskat)abstract
- Ni/NiO multilayers were grown by magnetron sputtering at room temperature, with the aid of the natural oxidation procedure. That is, at the end of the deposition of each single Ni layer, air is let to flow into the vacuum chamber through a leak valve. Then, a very thin NiO layer (similar to 1.2 nm) is formed. Simulated x-ray reflectivity patterns reveal that layering is excellent for individual Ni-layer thickness larger than 2.5 nm, which is attributed to the intercalation of amorphous NiO between the polycrystalline Ni layers. The magnetization of the films, measured at temperatures 5-300 K, has almost bulk-like value, whereas the films exhibit a trend to perpendicular magnetic anisotropy (PMA) with an unusual significant positive interface anisotropy contribution, which presents a weak temperature dependence. The power-law behavior of the multilayers indicates a non-negligible contribution of higher order anisotropies in the uniaxial anisotropy. Bloch-law fittings for the temperature dependence of the magnetization in the spin-wave regime show that the magnetization in the multilayers decreases faster as a function of temperature than the one of bulk Ni. Finally, when the individual Ni-layer thickness decreases below 2 nm, the multilayer stacking vanishes, resulting in a dramatic decrease of the interface magnetic anisotropy and consequently in a decrease of the perpendicular magnetic anisotropy. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4750026]
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| 2. |
- Poulopoulos, P., et al.
(författare)
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Growth and Magnetism of Natural Multilayers
- 2011
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Ingår i: Journal of Nano Research. - 1662-5250. ; 15, s. 95-103
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a simple method to fabricate high quality Ni/NiO multilayers with the use of a single magnetron sputtering head. Namely, at the end of the deposition of each single Ni layer, air is let to flow into the vacuum chamber through a leak valve. Then, a very thin NiO layer (similar to 1nm) is formed by natural oxidation. The process is reproducible and the result is the formation of a multilayer with excellent layering. Magnetization hysteresis loops recorded at 5 K and room temperature reveal a tendency for perpendicular magnetic anisotropy as the thickness of the individual Ni layers decreases. It is shown that the Ni/NiO interface has sizeable positive surface/interface anisotropy, i.e. it favors the development of perpendicular magnetic anisotropy. This is rather unusual for a Ni-based multilayered system and may render Ni/NiO multilayers useful for magneto-optical recording applications.
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| 3. |
- Poulopoulos, P., et al.
(författare)
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Positive surface and perpendicular magnetic anisotropy in natural nanomorphous Ni/NiO multilayers
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 96:20, s. 202503-
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Tidskriftsartikel (refereegranskat)abstract
- Ni/NiO multilayers with excellent sequencing are grown via radiofrequency magnetron sputtering with the use of one Ni target and natural oxidation. Ni layers consist of very small Ni nanocrystals interrupted by amorphous NiO layers. When Ni is deposited at 0.3 Pa Ar-pressure, the hard-magnetization axis is the film normal and saturation field decreases by decreasing Ni layer thickness. Considerable positive surface anisotropy is found, which is remarkable for Ni-based multilayers. If Ni is deposited at 3 Pa Ar-pressure, perpendicular magnetic anisotropy is observed at low temperatures even for 5.4 nm thick Ni layers. This anisotropy results in the formation of stripe magnetic domains.
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