Coexistence of ferromagnetic and antiferromagnetic phases in gadolinium-doped lanthanum(0.7) calcium(0.3) manganese oxygen(3)

Magnetic and electrical properties for La(1-x)Gd(x)0.7Ca(0.3)MnO3 were studied at ambient and high pressure. For x > 0.1 the ferromagnetic saturation moment M is smaller than that expected for complete ferromagnetic alignment of the Mn moments. Gd substitution lowers both the paramagnetic-ferromagnetic transition temperature T(C), the metal-insulator transition temperature T(MI) and dramatically increases the electrical resistivity rho. T(MI) is observed to be significantly lower than T(C) for x > 0.1. The disagreement of T(C) and T(MI) is a result of the A-site ion size difference which causes the coexistence of ferromagnetic La-Ca-Mn-O and antiferromagnetic Gd-Ca-Mn-O phases and leads to the anomalous electrical transport properties. Samples with the largest average A-site ionic radius <rA> show the highest T(C) or T(MI) and are least sensitive to pressure.