All wurtzite (In,Ga)As-(Ga,Mn)As core-shell nanowires

Structural and magnetic properties of (In,Ga)As-(Ga,Mn)As core−shell nanowires grown by molecular beam epitaxy on GaAs(111)B substrate with gold catalyst have been investigated. (In,Ga)As core nanowires were grown at high temperature (500 °C) whereas (Ga,Mn)As shells were
deposited on the {11̅00} side facets of the cores at much lower
temperature (220 °C). High-resolution transmission electron microscopy images and high spectral resolution Raman scattering data show that both the cores and the shells of the nanowires have wurtzite crystalline structure. Scanning and transmission electron microscopy observations show smooth (Ga,Mn)As shells containing 5% of Mn epitaxially deposited on (In,Ga)As cores containing about 10% of In without any misfit dislocations at the core−shell interface. With the In content in the (In,Ga)As cores larger than 5% the (In,Ga)As lattice
parameter is higher than that of (Ga,Mn)As and the shell is in the tensile strain state. Elaborated magnetic studies indicate the
presence of ferromagnetic coupling in (Ga,Mn)As shells at the temperatures in excess of 33 K. This coupling is maintained only
in separated mesoscopic volumes resulting in an overall superparamagnetic behavior which gets blocked below ∼17 K.