Carrier localization and out of plane anisotropic magnetoresistance in Nd0.55-xSmxSr0.45MnO3 thin films

The impact of carrier localization on the anisotropic magnetoresistance (AMR) has been investigated in Nd0.55-xSmxSr0.45MnO3 (x = 0.00-0.45) thin films. The substitution of smaller Sm3+ cations for larger Nd3+ reduces the average radius of the A-site of the perovskite lattice and enhances size disorder. This quenched disorder results in (1) enhanced Jahn-Teller (J-T) distortion as suggested by decrease in the out of plane lattice constant, (2) stronger carrier localization as evidenced by enhancement in the activation energy of small polaron hopping, (3) decrease in the ferromagnetic (FM) and insulator-metal transition (IMT) temperatures (T-C/T-IM), (4) sharpening of the IMT, (5) increase in the low field MR, and (6) large enhancement in the AMR. The AMR-T curves of all the films show a maximum just below T-IM. The peak AMR measured at small magnetic field of 4.2 kOe increases from -5% for x = 0.00 to -60% for x = 0.45. The enhancement in AMR has been explained in terms of the unquenching of the orbital angular momentum of t(2g)(3) and e(g)(1) configuration and spin fluctuations due to stronger J-T distortion at higher values of x. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4722815]