Collapse of ferromagnetism with Ti doping in Sm_0.55Sr_0.45MnO₃

Abstract

We have investigated the effect of Ti doping on the transport properties coupled with the magnetic ones in Sm_0.55Sr_0.45Mn1−ηTiηO3 (0 � η � 0.04). The parent compound, Sm_0.55Sr_0.45MnO₃, exhibits a first-order paramagnetic-insulator to ferromagnetic-metal transition just below Tc = 128 K. With the substitution of Ti at Mn sites (B site), Tc decreases approximately linearly at the rate of 22 K%−1 while the width of thermal hysteresis in magnetization and resistivity increases almost in an exponential fashion. The most spectacular effect has been observed for the composition η = 0.03, where a magnetic field of only 1 T yields a huge magnetoresistance, 1.2×107% at Tc ≈ 63 K. With increasing magnetic field, the transition shifts towards higher temperature side, and the first-order nature gets weakened and eventually becomes crossover above a critical field (Hcr) which increases with Ti doping. For η � 0.04, the system remains insulting without any ferromagnetic ordering down to 2 K. The Monte Carlo calculations based on a two-band double exchange model reveal that the rapid suppression of ferromagnetism with Ti doping is due to the increase of the lattice distortions around the doped Ti ions