Spin-polarized tunneling as a probe of the electronic properties of Ga1-x Mnx As heterostructures

We present magnetic and tunnel transport properties of (Ga,Mn) As/(In,Ga) As/Ga,Mn) As structure before and after adequate annealing procedure. The conjugate increase of magnetization and tunnel magnetoresistance obtained after annealing is shown to be associated with the increase of both exchange energy Δexch and hole concentration by reduction of the Mn interstitial atom in the top magnetic electrode. Through a 6×6 band k·p model, we established general phase diagrams of tunneling magnetoresistance (TMR) and tunneling anisotropic magnetoresistance (TAMR) vs (Ga,Mn)As Fermi energy (EF) and spin-splitting parameter (BG). This allows us to give a rough estimation of the exchange energy Δexch =6 BG -120 meV and hole concentration of the order of p=1×1020 cm-3 for (Ga,Mn)As and beyond gives the general trend of TMR and TAMR vs the selected hole band involved in the tunneling transport.