Physical properties of La0.67Ca0.33Mn0.9TM0.1O3 [TM = Fe, Co, Ni] and their spin dynamics in the paramagnetic regime studied by EPR

Substitution of Mn by Fe, Co, and Ni ions suppresses double exchange (DE), leading to a reduction in ferromagnetic interaction, or equivalently to lower values of Curie temperature, T-C. The intensity of the electron paramagnetic resonance (EPR) line decreases exponentially with temperature, and the temperature dependence of EPR, linewidth undergoes a minimum near T-C. The activation energy values, E-a, derived from the temperature dependence of EPB. line intensity, are equal to 0.074 eV, 0.093 eV and 0.086 eV for TM = Fe, Co, and Ni, respectively. In the case of cobalt substitution, an anomaly in the thermal evolution of the EPB. linewidth has been observed. We attribute the cause of this anomaly to a Jahn-Teller transition or an electronic phase separation.