Enhanced Ferromagnetism in Cylindrically Confined MnAs Nanocrystals Embedded in Wurtzite GaAs Nanowire Shells

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...

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Bibliographic Details
Published in:Nano letters 2019-10, Vol.19 (10), p.7324-7333
Main Authors: Kaleta, Anna, Kret, Slawomir, Gas, Katarzyna, Kurowska, Boguslawa, Kryvyi, Serhii B, Rutkowski, Bogdan, Szwacki, Nevill Gonzalez, Sawicki, Maciej, Sadowski, Janusz
Format: Article
Language:English
Subjects:
Fysik
magnetic nanocrystals
magnetic properties
molecular beam epitaxy
nanowires
Physics
Strain engineering
transmission electron microscopy
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Summary: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.
ISSN:1530-6984
1530-6992
1530-6992
DOI:10.1021/acs.nanolett.9b02956