Effect of Alloying with Ca in LaMnO3 System Studied by KKR-CPA Method and Giant Magnetoresistance
J. Tobola, S. Kaprzyk
Faculty of Physics and Nuclear Techniques, AGH, Al. Mickiewicza 30, 30-059 Kraków, Poland

and J. Pierre
Laboratoire de Magnetisme, L. Néel, CNRS, BP-166X Grenoble, France
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La1-x CaxMnO3 perovskites show semiconducting properties in the paramagnetic range. The gap is reduced near x=0.33, where ferromagnetic ordering is observed. The ferromagnetic ordering then induces a semiconductor-metal transition, and gives rise to a giant magnetoresistance effect. The ground state electronic structure calculations were done with KKR-CPA method for hypothetical cubic and ferromagnetic LaMnO3 and CaMnO3 compounds, as well as for disordered La1-xCaxMnO3 (x=0.33, 0.4, 0.5) alloys with real crystal data. As a result, we get a magnetic moment per formula 4.00μB and 3.00μB and half-metallic behaviour for end-compounds, respectively. In the ferromagnetic region a linear decrease in the magnetic moment of La1-xCaxMnO3 is observed, together with the decrease in the gap width for spin-down carriers, if doping Ca in La1-xCaxMnO3. A simple model is developed, which describes magnetic and transport properties as resulting from an exchange-induced band-crossing semiconductor-metal transition, as for instance in EuO.
DOI: 10.12693/APhysPolA.92.461
PACS numbers: 71.20.Lp, 71.20.-b