Effects of Fe doping in

The effect of Fe doping in the Mn site on the magnetic, transport and structural properties of polycrystalline La 1/2 Ca 1/2 MnO 3 was studied. Doping with low Fe concentration (< 10%) strongly affects electrical transport and magnetization. Long range charge order is disrupted even for the lowest doping level studied (~2%). For Fe concentration up to 5% a ferromagnetic state develops at low temperature with metallic like conduction and thermal hysteresis. In this range, the Curie temperature decreases monotonously as a function of Fe doping. Insulating behavior and a sudden depression of the ferromagnetic state is observed by further Fe doping. Mixed valence manganates Ln 1-x D x MnO 3+δ (where Ln is a lanthanide and D an alkaline earth ion) have been the subject of broad research because of the variety of properties they exhibit [1]. Among them, those compounds exhibiting charge order (CO) phenomena are being the focus of intense studies because percolative paths of coexisting ferromagnetic (FM) metallic phases are suspected to be responsible of colossal magnetoresistance[2]. The low temperature ordering of Mn +3 and Mn +4 can be destroyed by substitutionally induced cation disorder, either in the Mn site[3] or in the Ln-D site[4]. Also, application of magnetic field may lead to a charge melting [5] of the otherwise ordered lattice. The La 1/2 Ca 1/2 MnO 3 compound has antiferromagnetic (AFM) ground state with CO; upon warming, a first order phase transition to a FM state is observed. Thermal disorder inhibits charge localization and AFM coupling, and thereby the double exchange (DE) mechanism leads to a FM state. The subtle competition between FM and CO states gives rise to phase separation into nanodomains of FM and CO states below 150K [6]. We have studied the effect of Fe substitution in the Mn site of La 1/2 Ca 1/2 MnO 3. Low temperature long range CO is disrupted and a FM state is obtained for Fe concentration below 5%. By further Fe doping insulating behavior and a sudden depression of the ferromagnetic state is observed. Polycrystalline samples of La 1/2 Ca 1/2 Fe y Mn 1-y O 3 (0 < y < 0.1) were prepared by thermal decomposition of the corresponding citrates at 700 o C, followed by a heat treatment at 1000 o C for 10 hours. Powders were pelletized and sintered at the same temperature for 5 hours. X-ray powder diffraction data …