Interplay between the magnetic and transport properties in the III-V diluted magnetic semiconductor<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ga</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mi>−</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Mn</mml:mi></mml:mrow><mml:mrow><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mi mathvariant="normal">As</mml:mi></mml:math>

Using a low-temperature molecular-beam epitaxy growth procedure, ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ --- a III-V diluted magnetic semiconductor --- is obtained with Mn concentrations up to $x\ensuremath{\sim}9%.$ At a critical temperature ${T}_{c}$ (${T}_{c}\ensuremath{\approx}50\mathrm{K}$ for $x=0.03--0.05$), a paramagnetic to ferromagnetic phase transition occurs as the result of the interaction between $\mathrm{M}\mathrm{n}\ensuremath{-}h$ 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 $\ensuremath{\sim}10\mathrm{K}$) 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.

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