Collapse of ferromagnetism with Ti doping in Sm${}_{0.55}$Sr${}_{0.45}$MnO${}_3$: A combined experimental and theoretical study

Abstract

We have investigated the effect of Ti doping on the transport properties coupled with the magnetic ones in Sm${}_{0.55}$Sr${}_{0.45}$Mn${}_{1-\eta }$Ti${}_{\eta }$O${}_3$ ($0\le \eta \le 0.04$). The parent compound, Sm${}_{0.55}$Sr${}_{0.45}$MnO${}_3$, exhibits a first-order paramagnetic-insulator to ferromagnetic-metal transition just below $T_{\mathrm{c}}$ = 128 K. With substitution of Ti at Mn sites ($B$-site), $T_{\mathrm{c}}$ 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 $\eta$=0.03, where a magnetic field of only 1 T yields a huge magnetoresistance, $1.2\times 10^7$ $\%$ at $T_c\approx$ 63 K. With increasing magnetic field, the transition shifts towards higher temperature, and the first-order nature of the transition gets weakened and eventually becomes crossover above a critical field ($H_{cr}$) which increases with Ti doping. For Ti doping above 0.03, the system remains insulting without any ferromagnetic ordering down to 2 K. The Monte-Carlo calculations based on a two-band double exchange model show that the decrease of $T_{\mathrm{c}}$ with Ti doping is associated with the increase of the lattice distortions around the doped Ti ions.

15 pages, 6 figures