Memory Effects in Manganese Perovskites. Experiment and Theory
- PDF / 221,861 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 76 Downloads / 209 Views
0961-O05-10
Memory Effects in Manganese Perovskites. Experiment and Theory N. Noginova1, J. McClure1, V. Gavrilenko1, and D. Novikov2 1 NSU, Norfolk, VA, 23504 2 TIAX LLC, Cambridge, MA, 02140 Abstract. Electrically induced quasi-permanent changes in low-field conductivity have been observed in single crystals of LaGa1-xMnxO3 in the broad range of Mn ion concentrations. The memory effects can last for a long time at room temperature and can be easily erased by heating up to Tc ~300 C. The temperature dependence of the resistivity has a sharp drop around the phase transformation temperature, pointing to the role of phase transformation processes. The switching between high resistance and low resistance states is demonstrated. We explain our experimental data in terms of thermo induced local phase transition with the oxidation of Mn ions. The results of the ab initio calculations of the electron energy structure in Jahn-Teller-distorted and non-distorted cells confirm the mechanism suggested. Introduction. Manganites (such as La1-xSrxMnO3, La1-xSrxMnO3 and similar materials) are very interesting and complex systems, with strong correlation between electric, magnetic and lattice effects. Properties of these materials depend strongly on the composition, in particular, doping concentration of the divalent ion, i.e. relative content of Mn4+/Mn3+ ions. Irreversibility effects observed in magnetic and transport properties in different types of manganites [1-4] are commonly ascribed to intrinsic coexistence of two or more phases with different magnetic and transport properties on the submicrometer scale. The phase containing only Mn3+ ions is antiferromagnetic and insulating while the phase with Mn3+ and Mn4+ ions is ferromagnetic and conducting. Optical illumination, thermal, electric or magnetic field cycling may lead to changes in the phase content, reorientation and reshaping of the magnetic domains, causing the irreversibility in magnetic and electric behavior. However, this mechanism could not be fully applicable to explain irreversible effects in transport properties which have been observed in manganite systems with decreased content of Mn ions, LaGa1-xMnxO3 [5]. In contrast to the well-known manganite CMR systems, in these single crystalline materials, Mn3+ ions are diluted by nonmagnetic Ga ions, which enter the same place in the crystal structure as Mn ions. As it was recently reported, a significant increase in the low-field electrical conductivity was observed after application of high electric currents. The effect is quasi-permanent at room temperature demonstrating very slow recovering which follows approximately logarithmic time dependence. Heating of the sample above the phase transformation temperature resulted in the recovering of the initial resistance. Such behavior is very similar to optically induced effects in another class of Mn doped perovskite materials, Mn doped yttrium orthoaluminates with very low Mn concentration (0.1 at.% or less). Mn:YAlO3, high-quality optical single crystals, demonstrate s
Data Loading...
