Jahn-Teller distortion ordering in single-crystal Nd1/2Sr1/2MnO3

Charge, spin and orbital degrees of freedom play important roles in the electrical and magnetic properties of manganites. Nd0.5Sr0.5MnO3 is a paramagnetic insulator with Imma orthorhombic symmetry at room temperature. Upon cooling it becomes a ferromagnetic metal below 240 K and at 160 K undergoes a first-order phase transition. Below this temperature it is a CE-type antiferromagnetic insulator. In this paper we report synchrotron X-ray scattering investigations of superlattice reflections observed in the low temperature phase of Nd0.5Sr0.5MnO3. Upon cooling below 160 K we observed additional peaks occurring at non-integer positions in reciprocal space. These reflections had a wavevector (1/2,0,0) and are due to the structural modulation arising from the Jahn-Teller distortion associated with charge ordering of Mn3+ and Mn4+ ions and orbital ordering in the sample. The peaks observed below 160 K have an intensity of approximately 10-3 that of the Bragg reflections. The intensity profiles of these reflections show that the transition into the ordered phase is strongly first-order. The structural phase transition was observed to display a hysteresis width of 10 K. The measured widths of these peaks show that the charge modulation is correlated primarily in the ac plane rather than the K-direction (long-axis). (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)