| 1. |
- Gryglas-Borysiewicz, Marta, et al.
(författare)
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Hydrostatic pressure influence on T-C in (Ga,Mn)As
- 2020
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 101:5, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- The influence of hydrostatic pressure on the Curie temperature T-C of thin ferromagnetic (Ga,Mn)As layers is studied. New experimental data unambiguously point to both positive and negative pressure-induced changes of Curie temperature. The positive pressure coefficient is observed for samples with relatively high values of T-C and can be quantitatively described by the p-d Zener model of carrier-mediated ferromagnetism within the six-band k . p formalism and the ab initio approach. First-principles calculations of structural, electronic, and magnetic properties of (Ga,Mn)As show that antiferromagnetic coupling of substitutional Mn atoms with interstitial ones may account for a decrease of T-C under pressure in samples having a substantial concentration of interstitial Mn.
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| 2. |
- Kaleta, Anna, et al.
(författare)
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Enhanced Ferromagnetism in Cylindrically Confined MnAs Nanocrystals Embedded in Wurtzite GaAs Nanowire Shells
- 2019
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 19:10, s. 7324-7333
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Tidskriftsartikel (refereegranskat)abstract
- Nearly a 30% increase in the ferromagnetic phase transition temperature has been achieved in strained MnAs nanocrystals embedded in a wurtzite GaAs matrix. Wurtzite GaAs exerts tensile stress on hexagonal MnAs nanocrystals, preventing a hexagonal to orthorhombic structural phase transition, which in bulk MnAs is combined with the magnetic one. This effect results in a remarkable shift of the magneto-structural phase transition temperature from 313 K in the bulk MnAs to above 400 K in the tensely strained MnAs nanocrystals. This finding is corroborated by the state of the art transmission electron microscopy, sensitive magnetometry, and the first-principles calculations. The effect relies on defining a nanotube geometry of molecular beam epitaxy grown core-multishell wurtzite (Ga,In)As/(Ga,Al)As/(Ga,Mn)As/GaAs nanowires, where the MnAs nanocrystals are formed during the thermal-treatment-induced phase separation of wurtzite (Ga,Mn)As into the GaAs-MnAs granular system. Such a unique combination of two types of hexagonal lattices provides a possibility of attaining quasi-hydrostatic tensile strain in MnAs (impossible otherwise), leading to the substantial ferromagnetic phase transition temperature increase in this compound.
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| 3. |
- Kowalik, Iwona Agnieszka, et al.
(författare)
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Stable antiferromagnetic nanocrystals for room temperature applications : the case of iron nitride
- 2019
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Ingår i: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 7:31, s. 9474-9480
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Tidskriftsartikel (refereegranskat)abstract
- We characterise the magnetism of self-assembled FenN nanocrystals, combining core level spectroscopy with first-principles theory. Not only ferromagnetic but also antiferromagnetic iron nitride nanocrystals are identified, exhibiting stable magnetic properties at room temperature. New stable magnetic phases are found, previously believed to order magnetically only well below room temperature. As determined by the growth conditions, several phases of magnetic FenN nanocrystals are identified in the near surface region of GaN based thin films, with typical dimensions from 50 to 100 nm, embedded in the (Ga,Fe)N lattice or residing on the GaN surface. We determine, at room temperature, Fe4N and Fe3N ferromagnetic nanocrystals, as well as Fe2N and FeN nanocrystals in an antiferromagnetic state, which is not stable at room temperature in their bulk phases.
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