  We present studies of structural, magnetic and electrical properties of
Zn/1-x-y/Cd/x/Mn/y/GeAs/2/ nanocomposite ferromagnetic semiconductor samples
with changeable chemical composition. The presence of MnAs clusters induces in
the studied alloy room temperature ferromagnetism with the Curie temperature,
TC, around 305 K. The chemical composition of the chalcopyrite matrix controls
the geometrical parameters of the clusters inducing different magnetoresistance
effects in the crystals. The presence of ferromagnetic clusters in the alloy
induces either negative or positive magnetoresistance with different values.
The Cd-content allows a change of magnetoresistance sign in our samples from
negative (for x = 0.85) to positive (for x = 0.12). The negative
magnetoresistance present in the samples with x = 0.85 is observed at
temperatures T < 25 K with maximum values of about -32% at T = 1.4 K and B = 13
T, strongly depending on the Mn content, y. The positive magnetoresistance
present in the samples with x = 0.12 is observed with maximum values not
exceeding 50% at B =13 T and T = 4.3 K, changing with the Mn content, y.
