During the last decade, R1−xAxMnO3 pseudocubic manganites (R is a rare-earth metal: La, Pr, Nd, Dy; A is an alkaline earth: Sr, Ca, Ba, Pb) have attracted much attention due to their unique spin-dependent magneto-transport properties. The strong interplay between charge, spin, orbital and lattice degrees of freedom in these materials leads to a variety of phases, such as ferromagnetic metallic (FMM), antiferromagnetic insulator (AFI), ferromagnetic insulator (FMI), cluster glass, spin glass and orbitally ordered (OO), antiferromagnetic canted (AFC) and orbitally ordered and charge orbitally ordered (COO). From the technological point of view, the most interesting property of these systems is the colossal magnetoresistance (CMR), which occurs near the Curie temperature TC, when the oxides undergo a transition from the paramagnetic (PM) to the FM state. The magnetic and transport properties of manganites are believed to be determined by a competition between the superexchange (SE) interaction and the double-exchange (DE) mechanism. Further studies on these materials have shown that other mechanisms influence the phase transitions, among them the electron–phonon interaction arising from the Jahn–Teller (JT) distortion, the orbital ordering, the electron–electron correlations and the coupling between spin and orbital structure.

     In this project we use infrared spectroscopy together with magnetic and transport measurements to study optimally doped La1−x SrxMn1−zBzO3 (B = Cu, Zn; 0.17 < x < 0.30, 0< z< 0.1) manganites. With optimum doping we accomplished the minimum vacancies at the A and the B sites, the strongest colossal magnetoresistance effect and we also excluded the possibility of long range charge/orbital ordering. On the other hand, the B site doping offers us the possibility of reducing the concentration of free carriers (the Drude term in the optical conductivity). By comparing the results from optical reflectivity with transport and magnetization measurements we will be able to consider an influence of B site doping on phase transitions and charge/orbital ordering in these oxides.

Center for Solid State and New Materials :: Research :: Activity 2 :: print