Anomalous magneto-transport behaviour near the first order phase transition in Gd(5)Ge(3.8)Ga(0.2) alloy.

We study the effect of Ga doping at the Ge site of the metamagnetic compound Gd(5)Ge(4). For 5% Ga doping, the resulting alloy (Gd(5)Ge(3.8)Ga(0.2)) shows antiferromagnetic ordering around 130 K, and a thermally driven first order magneto-structural transition at low temperature leading to the ferromagnetic ground state. The alloy shows a noticeable amount of training effect in resistivity when thermally cycled through this first order phase transition (FOPT). The training effect is present in the case of isothermal field cycling. The FOPT region is found to be metastable and extremely sensitive to the applied magnetic field with a clear signature of a metamagnetic transition in the magnetization and resistivity. The metastability is further supported by the large relaxation observed in the resistivity. The giant magnetoresistance observed in the sample is found to be positive near the FOPT, while below the transition it is negative. The resistivity shows irreversibility due to field cycling, which is related to both a field-induced arrested state and some permanent micro-structural changes in the sample.