Band structure evolution and the origin of magnetism in (Ga,Mn)As: From paramagnetic through superparamagnetic to ferromagnetic phase

Abstract

The high-spectral-resolution spectroscopic studies of the energy gap evolution, supplemented with electronic, magnetic and structural characterization, show that the modification of the GaAs valence band caused by Mn incorporation occurs already for a very low Mn content, much lower than that required to support ferromagnetic spin -spin coupling in (Ga,Mn)As. Only for n-type (Ga,Mn)As with the Mn content below about 0.3% the Mnrelated extended states are visible as a feature detached from the valence-band edge and partly occupied with electrons. The combined magnetic and low-temperature photoreflectance studies presented here indicate that the paramagnetic -ferromagnetic transformation in p-type (Ga,Mn)As takes place without imposing changes of the unitary character of the valence band with the Fermi level located therein. The whole process is rooted in the nanoscale fluctuations of the local (hole) density of states and the formation of a superparamagnetic-like state. The Fermi level in (Ga,Mn)As is coarsened by the carrier concentration of the itinerant valence band holes and further fine-tuned by the many-body interactions.

Ba(Zn,Co)2As2 : A diluted ferromagnetic semiconductor with nGuo1, Man2, Wang3 et al. 2019Phys. Rev. B201190View full textAdd to dashboardCite

“…This feature may be helpful for obtaining higher T C in n-type DMS systems. Another concern we should note is the superparamagnetic-like fragments caused by the fluctuations of the carrier density [46][47][48][49] . If the dynamic frequency of these superparamagnetic-like fragments is smaller than the lower frequency limit of µSR that is ∼ 10 4 Hz, µSR will treat them static.…”

Site-specific atomic order and band structure tailoring in the diluted magnetic semiconductor (In,Ga,Mn)As

“…From micro-Raman spectra, the hole concentrations have been estimated to be about 10 19 and 10 20 cm −3 in the films with 2.5% and 5.6% Mn content, respectively [44,45]. The obtained results suggest that, similarly to (Ga,Mn)As [44], the (In,Ga,Mn)As film with 2.5% Mn shows properties of an insulator-like material whereas the film with 5.6% Mn is similar to a metallic one [46].…”

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

“…43 So, as long as the growth conditions are not altered, 44 there can only be fluctuations in the local density of states that could end up in a patchwork of spontaneously magnetized volumes (T C > T 0 ) containing a sufficiently high hole density to assure the FM spin-spin ordering within their phase coherence length. In this scenario the rest of the material with too low hole density to mediate the effective coupling remains nonmagnetic at the relevant temperature range (T > T 0 ), 40,45 where T 0 is the base temperature of an experimental setup.…”