Effect of substitution of Cr on magnetic behaviour of bilayered manganite La1.2Sr1.5Ca0.3Mn2O7

Magnetic behaviour has been investigated of bilayered perovskites La1.2Sr1.5Ca0.3Mn2O7 and La1.2Sr1.5Ca0.3Mn1.95Cr0.05O7. Magnetization - temperature measurements of the system without Cr show one transition at ∼ 270K, a cusp at ∼ 220K and another transition at ∼75K; for the system with Cr these temperatures are ∼260K, ∼200K and ∼90K. Thus substitution of low amount of Cr in the Ca substituted system strengthens the double exchange. Application of magnetic field causes the low temperature peak to shift to lower temperatures showing that the 3D ferromagnetic state is a short range type. Hysteresis in M-H curve is the lowest at a temperature below the cusp temperature which supports the assignment of the cusp to spin glass like phase. (author)