| 1. |
- Sawicki, M., et al.
(författare)
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Homogeneous and heterogeneous magnetism in (Zn,Co)O : From a random antiferromagnet to a dipolar superferromagnet by changing the growth temperature
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:8
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Tidskriftsartikel (refereegranskat)abstract
- A series of (Zn,Co)O layers with Co contents x up to 40% grown by atomic layer deposition have been investigated. All structures deposited at 160 degrees C show magnetic properties specific to II-VI dilute magnetic semiconductors with localized spins S = 3/2 coupled by strong but short-range antiferromagnetic interactions resulting in low-temperature spin-glass freezing for x = 0.16 and 0.4. At higher growth temperature (200 degrees C) metallic Co nanocrystals precipitate in two locations giving rise to two different magnetic responses: (i) a superparamagnetic contribution coming from volume disperse nanocrystals; (ii) a ferromagneticlike behavior brought about by nanocrystals residing at the (Zn,Co)O/substrate interface. It is shown that the dipolar coupling within the interfacial two-dimensional dense dispersion of nanocrystals is responsible for the ferromagneticlike behavior.
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| 2. |
- Kowalik, I. A., et al.
(författare)
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Element-specific characterization of heterogeneous magnetism in (Ga,Fe)N films
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:18, s. 184411-
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Tidskriftsartikel (refereegranskat)abstract
- We employ x-ray spectroscopy to characterize the distribution and magnetism of particular alloy constituents in (Ga,Fe)N films grown by metal organic vapor phase epitaxy. Furthermore, photoelectron microscopy gives direct evidence for the aggregation of Fe ions, leading to the formation of Fe-rich nanoregions adjacent to the samples surface. A sizable x-ray magnetic circular dichroism (XMCD) signal at the Fe L edges in remanence and at moderate magnetic fields at 300 K links the high-temperature ferromagnetism with the Fe(3d) states. A sizable value of the orbital moment measured in remanence points to a large magnetic anisotropy and to a correspondingly high blocking temperature, which can stabilize the ferromagnetic-like response of the Fe-rich nanocrystals at 300 K. The XMCD response at the N K edge highlights that the N(2p) states, due to exchange coupling to Fe ions, carry considerable spin polarization. These results, supported by ab initio studies of XMCD spectra for various FeN delta nanocrystals, demonstrate that nanocrystals with delta > 0.25 account for the ferromagnetic behavior of (Ga,Fe)N films.
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| 3. |
- Racka, K., et al.
(författare)
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Growth of SiC by PVT method in the presence of cerium dopant
- 2013
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 377, s. 88-95
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the presence of CeO2 in the source material on the properties of SiC crystals grown by Physical Vapor Transport (PVT) method is investigated. The doping efficiency and, indirectly, the presence of the cerium vapour in the growth atmosphere were examined by study of structural, electrical and optical properties of the crystals. X-ray photoelectron spectroscopy shows that Ce2O3 and CeO2 coexist on the SiC post-growth surfaces. A detectable Ce incorporation is observed only in the last grown part of the crystal.
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