Competition between metal-semiconductor and charge ordering transitions in the CMR ceramic Pr12 − xYxSr12MnO3

Abstract The systematic study of the solid solution Pr 1 2 − x Y x Sr 1 2 MnO 3 shows the coexistence of two types of CMR effect on the same sample associated with a transition from an antiferromagnetic semiconducting to a ferromagnetic metallic state (at T co ) and then to a paramagnetic semiconducting state (at T C ) as T increases. The competition between these two types of CMR effect is shown for the first time. For low x values, T co (for charge ordering) increases and T C decreases as the mean size of the interpolated cation decreases. Beyond a critical x value the two antagonist effects interpenetrate each other so that they tend to disappear. The ρ ( T ) curves, registered in the Earth's magnetic field ( B = 0) and in B = 5 T show a negative CMR effect similar to that observed for Pr 1 2 Sr 1 2 MnO 3 , i.e. a R 0 / R B = 5 T ≅ 10 2 at 120 K for x = 0.04. It is remarkable that the application of a magnetic field has the same effect as increasing the size of the interpolated cation: it decreases T co and increases T C . The electron microscopy study of these samples shows that they exhibit a ‘pure’ body centered cell (Imma) derived from the perovskite ( a ≈ c ≈ a p √2 and b ≈ 2 a ).