Magnetic and electrical properties of(La1−xDyx)0.7Ca0.3MnO3perovskites

Abstract

The effect of substituting La with Dy in the ferromagnetic perovskite La 0 . 7 Ca 0 . 3 MnO 3 has been studied in the series (La( 1 - x )Dy x ) 0 . 7 Ca 0 . 3 MnO 3 (x= 0, 0.114, 0.243, and 0.347). Magnetic and transport properties have been measured using ac susceptibility, dc magnetization, neutron-depolarization, neutron-diffraction, and resistivity techniques. These studies show that an increase in Dy concentration suppresses the low-temperature ferromagnetic ground state, driving the system (for x=0.114 and 0.243) first into a randomly canted ferromagnetic state with a reduced metal-insulator transition temperature and then (for x = 0.347) to an ''insulating cluster-spin-glass state. Such deterioration of ferromagnetism and metallic conduction with Dy substitution is explained on the basis of a decrease in the transfer integral, t o (describing the hopping of e g electrons between Mn 3 + and Mn 4 + , known as ferromagnetic double-exchange interaction), resulting from an increase in the structural distortion. The randomly canted ferromagnetic state and the cluster-spin-glass state for x = 0.243 and 0.347 compounds, respectively, have been confirmed by neutron-depolarization measurements. These observed features have been attributed to a competition between the coexisting ferromagnetic double-exchange and the antiferromagnetic superexchange interactions in the distorted structures with reduced geometrical tolerance factor t and the randomness resulting from the random substitutions of La 3 + with Dy 3 + .