New mechanism of magnetoresistivity in itinerant metamagnets with a structural disorder is introduced basing on analysis of experimental results on magnetoresistivity, susceptibility, and magnetization of structurally disordered alloys (Y_1-xGd_x)Co_2. In this series, YCo_2 is an enhanced Pauli paramagnet, whereas GdCo_2 is a ferrimagnet (T_ c=400 K) with Gd sublattice coupled antiferromagnetically to the itinerant Co-3d electrons. The alloys are paramagnetic for x < 0.12. Large positive

more »

... resistivity has been observed in the alloys with magnetic ground state at temperatures T<T_ c. We show that this unusual feature is linked to a combination of structural disorder and metamagnetic instability of itinerant Co-3d electrons. This new mechanism of the magnetoresistivity is common for a broad class of materials featuring a static magnetic disorder and itinerant metamagnetism.