Study of the Magneto-Resistivity and Dependence of Percolation in La0.75Ca0.1Sr0.15Mn1?x Ga x O3 Compounds

We present a study of the effect of Ga-doping on the physical properties of La_0.75Ca_0.1Sr_0.15Mn_1?x Ga _x O₃ (x=0.025, 0.075 and 0.1) compounds prepared by the sol-gel method. The variation of the magnetization (M) vs. temperature (T), under an applied magnetic field of 0.05 T, reveals a ferromagnetic–paramagnetic transition for all samples. The magnetization behavior and the Curie temperature T _C have shown a large dependence on the fractional composition x. In fact, the M(T) curves have revealed the presence of a long-range ferromagnetic state below T _C. The magnetotransport properties have been investigated based on the temperature dependence of the resistivity ρ(T) measurements. We have noted that these samples present an electrical transition from a paramagnetic-semiconductor state to a ferromagnetic-metallic one, when decreasing temperature. We have used the phenomenological equation for conductivity under a percolation approach, which is based upon an approach that the system consists of the phase separated ferromagnetic metallic and paramagnetic insulating regions. We have then fitted the resistivity data measured in the range of 15–300 K and found that the activation barrier decreases with the raising Ga³⁺ ion concentration.