Signature of ferromagnetism, antiferromagnetism, charge ordering and phase separation by electron paramagnetic resonance study in rare earth manganites, Ln_(1-x)A_xMnO_3 (Ln=rare earth, A=Ca, Sr)

摘要

Phase separation has been recognized as an important ingredient to create the colossal magnetoresistance (CMR). To be able to characterize the phase separation signature by electron spin resonance (ESR), a preliminary work has been undertaken in order to check typical ESR behaviours of prototype manganites. These behaviours are antiferromagnetism (A-type, CE-type), charge order, ferromagnetism and phase separation. Five compounds were chosen, each of them exhibiting a specific characteristic (e.g., Pr_(0.4)Ca_(0.6)MnO_3 undergoes a charge ordered state followed by a antiferromagnetic state at lower temperature). The onset of the transitions has been determined from the temperature dependence of four main parameters deduced from the ESR spectra, the geff factor, the linewidth DELTA H_(pp). the intensity and the line asymmetry.