Magnetoresistance Behavior in La0.7CaxMnO3 (x = 0.1-0.3) and LayMnO3 (y = 0.67-0.9) Bulk Materials

In the mix-doped La0.7CaxMnO3 (x = 0–0.3) and self-doped LayMnO3 (y = 0.67–0.9) bulk materials a large magnetoresistance effect in the temperature range of 80–250 K has been observed. Depending on the doping extent the magnetoresistance ratio varies in the range of 10–30% under an applied field of 0.8 T. The insulator to metal transition shifts towards higher temperature with increasing y and x. This shift tendency indicates that in this case the effect of the AMnO3 lattice, such as the average ion radius in A-site (or the tolerance) and the variance of A-cation radius distribution, plays an important role in controlling the insulator to metal transition. An additional small peak of resistance versus temperature was observed around 170–200 K in the LayMnO3 bulk materials, which gives a beneficial contribution to the large magnetoresistance ratio at low temperature. A linear decrease of low field ac magnetic susceptibility with decreasing temperature was observed below Curie temperature. The small resistance peak and the linear decrease of magnetic susceptibility may be understood qualitatively in terms of phase separation.