Giant magnetoresistance properties of the La1−2xRxAxMnO3 (R=Nd, A=Ca) perovskites

Abstract

The effect of simultaneous substitution of Nd and Ca in the antiferromagnetic insulator, LaMnO3, is studied by x-ray diffraction, magnetoresistance, and magnetization measurements. X-ray powder diffraction patterns of La1−2xNdxCaxMnO3 polycrystalline bulk samples for x=0.2, 0.33, and 0.4 confirm the single-phase formation of orthorhombic perovskite structure (space group Pbnm). The unit cell volume decreases with increasing Nd/Ca substitution. Changes in the temperature dependence of resistivity from semiconducting to metallic, and an increase of the ferromagnetic transition temperature, are observed in this series with increasing x. For x=0.2, 0.33, and 0.4, the metal-insulator transition temperature (Tp) is 72, 140, and 155 K, respectively, and the magnetoresistance (MR) observed in this system in 2 T applied magnetic field around Tp is 35%, 99% and 65%, respectively. The MR of 99% for the x=0.33 sample is promising for practical device applications where MR at low fields is of special interest. The magnetic moment values, obtained from the magnetization data in the magnetically ordered state, agree reasonably well with the free ion Mn moments for all the samples.