Jahn‐Teller distortion ordering in single‐crystal Nd _1/2 Sr _1/2 MnO ₃

Abstract

Charge, spin and orbital degrees of freedom play important roles in the electrical and magnetic properties of manganites. Nd 0.5 Sr 0.5 MnO 3 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 firstorder 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 Nd 0.5 Sr 0.5 MnO 3 . Upon cooling below 160 K we observed additional peaks occurring at noninteger 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 Mn 3+ and Mn 4+ 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).

Anomalies of ultrasonic velocities, attenuation and elastic moduli in Nd 1− x Sr x MnO 3 perovskite manganite materials

“…The CO phenomenon is expected in Nd 1Àx Sr x MnO 3 in the doping range of 0.3rxr0.5 due to smaller ionic radius of Nd (1.123é) than ionic radii of Pr (1.13é) and La (1.172é) [32]. The CO properties that are characterised by a transition from an AFM insulating to a FM metallic state as temperature increases have been evidenced in Nd 0.5 Sr 0.5 MnO 3 with a transition temperature at 160 K [33]. The electron spins resonance (ESR) of polycrystalline CMR manganite with yttrium and barium doping have been studied in Nd 0.55 Sr 0.45 MnO 3 perovskite manganite materials [34].…”