Reversible change of charge ordering transition temperature in La _(0.5)Ca_(0.5+x)MnO_(3-y+Δy) induced by electric pulses

摘要

Specific heats and magnetic moments of La_(0.5)Ca _(0.5+x)MnO_(3-y+Δy) polycrystalline ceramics were measured under different resistance states induced by electric pulses. Experimental results revealed that the specific heat associated with ferromagnetic spin waves had a larger value at a low resistance state compared to that at a high state, indicating the growth of ferromagnetic regions as the resistance changed from a high state to a lower one. The charge ordering temperature (TCO) at a low resistance state was higher than that at a high state, in contrast to the prediction based on the traditional double exchange model. We proposed that the ferromagnetic clusters at a low resistance state would cause a reduction of the collective JahnTeller distortion in the ferromagnetic phase, thus leading to an increase in TCO.