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DC magnetization and electrical resistance measurements have been made on four samples in the series La 1.2 Sr 1.5 Ca 0.3 Mn 2-x Cr x O 7 corresponding to x = 0, 0.01, 0.03 and 0.05. The systems show onset of 3D ferromagnetic (FM) state in the temperature range ∼75–90 K Magnetization–temperature measurements in zero field cooling and field cooling modes, made under different external fields show long time evolution of magnetization with time suggestive of FM disorder and high magnetic anisotropy. At two temperatures above the Curie point of ∼75–90 K, broad discontinuities are seen in the range ∼260–270 K and ∼200–220 K. These might be signatures of transitions to FM order in ab plane and to an AFM state, respectively. An alternative explanation for the two higher temperature discontinuities could be in terms of a possible intergrowth in the ab plane reported in bi-layered systems. Insulator–metal transition temperature lies close to T c but the system with 2.5 atomic percent Cr ( x = 0.05) does not attain metallic state down to 20 K. Estimated values of density of states at Fermi energy and Debye temperature, for the studied compositions, are in reasonably good agreement with those reported in other perovskites. |
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