Anomalous ferromagnetic behavior and large magnetoresistance induced by orbital fluctuation in heavily doped Nd$_{1-x}$Sr$_x$MnO$_3$ (0.57 $\le$ $x$ $\le$ 0.75)
D. Akahoshi, R. Hatakeyama, M. Nagao, T. Asaka, Y. Matsui, and H. Kuwahara

We have elaborately investigated heavily-doped Nd$_{1-x}$Sr$_x$MnO$_3$ with $x = 0.57-0.75$. $3z^{2}-r^{2}$ and $x^{2}-y^{2}$ orbital orders strongly compete with each other at $x = 0.625$. The competition causes spatial orbital fluctuation on nanometer-scale below the orbital ordering temperature ($T_{\rm OO} \sim$ 500 K), which is evidenced by the observation of tweed structure using transmission electron microscopy. The orbital fluctuation, which persists down to lowest temperatures, gives rise to anomalous ferromagnetic behavior and concomitant large magnetoresistance well below the N\'eel temperature ($T_{\rm N}$ = 220 K).

© 2008 The American Physical Society.