Possible role of phase segregation in the disagreement between the metal-insulator and ferromagnetic transition temperatures in some colossal magnetoresistance compounds - art. no. 174436

摘要

The isovalent substitution of Gd for La in La0.7Ca0.3MnO3 lowers the paramagnetic-ferromagnetic transition temperature T-c and metal-insulator transition temperature T-MI with a substantial increase in the electrical resistivity rho. Reduction of the ferromagnetic saturation moment M (5 K) below that expected for complete ferromagnetic alignment of the Mn magnetic moments occurs and T-MI is significantly lower than T-c for x > 0.2. The observations are consistent with the existence of a granular mixture of ferromagnetic/conducting La-Ca-Mn-O and ferrimagnetic/insulating Gd-Ca-Mn-O. The ionic radius of the substituted rare-earth ion is found to be an important factor in determining whether or not granular behavior occurs. The results provide insight into why T-c not equal T-MI in some colossal magnetoresistance oxides. [References: 27]