Magnetoresistive properties of Sr 4-x Lax Mn3O10

Abstract

A series ofpolycrystaUine bulk samples of Sr.",LaxMnJOIOwere prepared using conventional solid state reaction technique and sintered at temperature !lOOT for 5 hours. The magnetoresistive properties of the polycrystalJine bulk samples were investigated from room temperarure down to liquid nitrogen temperature using standard four-probe technique. Analysis of X-ray diffraction pattern gives the single-phase structure of all the polycrystalJine samples without any trace of impurity. The transition between ferromagnetic metallic WId paramagnetic insulating states in Sr,_,La.Mn10IO perovskites is characterized by a maximum in the electrical resistivity at transition temperature. The transport behavior especially the metal-insulator (M-I) transition in mangenites Sr4-xLa"MnjOIOmay be understood in terms of the double exchange mechanisms which involves the ferromagnetic coupling between MnJ'(t~, e~) and Mn4+(ti. e;) spins. As a result of strong Hund's exchange coupling, tbe itinerant e~electrons (holes) interact with the localized Ii, electrons, and thus medIate ferromagnetic ordering and thc simultaneous M-I transition. Substitution of La in place of Sr enhances % of MnJ+ which ultimately increases M-I transition temperature in these manganites. The M-l transition temperature is also found to increases due to the external magnetic field. The external field might suppress the spin fluctuations which improves the conductivity. The characteristic magnctoresistance was measured both at room temperature and liquid nitrogen temperature. At room temperature MR is very low and almost linear with field. At 78 K a sharp increase of MR was observed at low magnetic field but the MR gradually decreases with the increase of applied magnetic field. The activation energy curves show that the conduction occurred just above transition temperature through a thermally activated process.