Rashid Gareev

Carrier-induced ferromagnetism in Ge(Mn,Fe) magnetic semiconductor thin-film structures

We report on the carrier-induced ferromagnetism in Ge(Mn,Fe) magnetic semiconductor insulating-type thin-film structures prepared using sequential deposition at Tg=520K with subsequent annealing at Tg. In the resulting films Mn and Fe are diffused in the Ge matrix without compromising the epitaxial structure. The anomalous Hall effect serves as a manifestation of the carrier-induced magnetism, with p-type conductivity and the Curie temperature TC=209K. The additional doping with Fe stabilizes epitaxial growth and carrier-mediated magnetism at levels of magnetic doping exceeding 10%. We conclude that indirect ferromagnetic exchange is mediated by localized holes with concentration n∼1020cm−3 and mobility μ∼10cm2∕(Vs).

Giant anisotropic magnetoresistance in insulating ultrathin (Ga,Mn)As

Molecular-beam epitaxy grown, 5 nm thick annealed Ga0.95Mn0.05As films demonstrate transition from metallic to insulating state for sheet resistances near resistance quantum, which we connect with the two-dimensional hole localization. Below the metal-insulator transition we found the giant anisotropic magnetoresistance (GAMR) effect, which depends on the orientation of magnetization to crystallographic axes and demonstrates the twofold symmetry angular dependence. The GAMR manifests itself in positive magnetoresistance near 50% at T=1.7 K for H//[110] crystallographic direction in contrast to smaller negative magnetoresistance for H//[1[overline 1]0] direction. We connect the GAMR with formation of high- and low-resistance states with different localization due to anisotropic spin-orbit interaction.

Resonant tunneling magnetoresistance in antiferromagnetically coupled Fe-based structures with multilayered Si/Ge spacers

We report on the experimental evidence of the tunneling magnetoresistance (TMR) effect near 3% and its inversion in strongly antiferromagnetically coupled Fe(001)∕([Si(0.2nm)∕Ge(0.2nm)]*5)∕Fe epitaxial structures with diffused interfaces. We explain the inversion of TMR with biasing voltage by resonant tunneling across impurity states with weak spin split ΔE∼10meV and spin-dependent filtering in the spacer layer. The resonant tunneling is manifested in spin-dependent resonances close to zero biasing voltages related to antiferromagnetic coupling across impurity states.