Twinning microstructure and charge ordering in the colossal magnetoresistive manganite Nd(sub 1/2)Sr(sub 1/2)MnO(sub 3)

摘要

Charge ordering (C.O.) in the colossal magnetoresistive (CMR) manganites gives rise to an insulating, high-resistance state. This charge ordered state can be melted into a low-resistance metallic-like state by the application of magnetic field. Thus, the potential to attain high values of magnetoresistance with the application of small magnetic fields may be aided by a better understanding of the charge-ordering phenomenon. This study focused on microstructural characterization in Nd (sub 12)Sr(sub 12)MnO(sub 3). In Nd(sub 12)Sr(sub 12)MnO(sub 3), the nominal valence of Mn is 3.5+. On cooling, charge can localize and lead to a charge ordering between Mn3+ and Mn4+. The ordering of charge results in a superlattice structure and a reduction in symmetry. Thin foil specimens were prepared from bulk samples by conventional thinning and ion milling at LiqN(sub 2)(L temperature) methods. The room temperature TEM observation of Nd(sub 12) Sr(sub 12)MnO (sub 3) reveals a highly twinned microstructure, together with a small number of stacking faults (SFS). A figure shows the same area of the specimen at different zone axes obtained by tilting around two perpendicular directions as indicated. Three grains A, B and C are labeled for each of the zone axes. The room temperature EDPs from the matrix and twins shows an approximate 90 (degree) rotation suggesting a 90 (degree) twin orientation. These results are further confirmed by C.O. at low temperatures. The twinning planes can be determined by tilting with large angles.