Interplay between the magnetic and transport properties in the III-V diluted magnetic semiconductorGa1−xMnx

Abstract

Using a low-temperature molecular-beam epitaxy growth procedure, Ga 1Ϫx Mn x As -a III-V diluted magnetic semiconductor -is obtained with Mn concentrations up to xϳ9%. At a critical temperature T c ͑T c Ϸ50 K for xϭ0.03-0.05͒, a paramagnetic to ferromagnetic phase transition occurs as the result of the interaction between Mn-h complexes. Hole transport in these compounds is strongly affected by the antiferromagnetic exchange interaction between holes and Mn 3d spins. A model for the transport behavior both above and below T c is given. Above T c , all materials exhibit transport behavior which is characteristic for systems near the metal-insulator transition. Below T c , due to the rising spontaneous magnetization, spin-disorder scattering decreases and the relative position of the Fermi level towards the mobility edge changes. When the magnetization has reached its saturation value ͑below ϳ10 K͒ variable-range hopping is the main conduction mechanism. The negative magnetoresistance is the result of the expansion of the hole wave functions in an applied magnetic field. ͓S0163-1829͑97͒04044-7͔

Variable-range hopping of spin polarons: Magnetoresistance in a modified Mott regime

“…Giant negative magnetoresistance in the variable-range hopping region apparently has been observed in recently discovered dilute magnetic semiconductors, such as GaAs:Mn [5,6,7] and MnGe [21] below the metal-insulator transition point. In all these materials, magnetoresistance is described by Eq.…”

“…Recent technological developments in producing novel dilute magnetic semiconductors, especially GaAs : Mn, and magnetic nanostructures, such as GaAs/ErAs, made it possible to observe electrical conductivity due to hopping via magnetic impurities [5] and nano-islands [16] thus revealing a rich interplay of magnetic and electrical transport properties. For instance, Mn atoms play a dual role as acceptor sites and magnetic ions in GaAs resulting in the very unusual magnetic properties of this material [5,17].…”

“…The temperature dependence of the VRH conductivity is described by stretched exponents σ ∝ exp (−T /T 0 ) p and depending on the value of p can be attributed to one of the two major regimes such as the Mott (p = 1/4) and the Shklovskii-Efros (p = 1/2) regimes [1,2]. Several observations of giant and colossal negative VRH magnetoresistance in systems with strong spin disorder such as dilute magnetic semiconductors (DMS) have been reported recently [5,6,7]. It seems rather natural to attribute VRH magnetoresistance to spin polarons that are believed to be a major cause of negative magnetoresistance in DMS [8,9,10].…”

The essential role of carefully optimized synthesis for elucidating intrinsic material properties of (Ga,Mn)As

“…To circumvent the solubility problem, a non-equilibrium, low-temperature molecular-beam-epitaxy (LT-MBE) technique was employed, which led to first successful growths of (Ga,Mn)As ternary alloys with more than 1% Mn and to the discovery of ferromagnetism in these materials [1][2][3][4] . The compounds qualify as ferromagnetic semiconductors to the extent that their magnetic and other properties can be altered by the usual semiconductor electronics engineering variables, such as doping, electric fields, or light.…”

Diluted Magnetic III-V Semiconductors

“…For a long time these materials were unavailable, since it was not possible to obtain III-V crystals with a reasonable concentration of magnetic ions. Only the application of MBE methods resulted in crystals with few molar percent of Mn [10][11][12][13][14][15][16][17][18][19][20][21][22]. Both quasi 3D epilayers, as well as quantum structures were obtained [18].…”