Creation of room-temperature-multiferroic oxides and electric-field-controlled magnetization

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New materials exhibiting a large magnetoelectric effect due to coexistence of ferromagnetism and ferroelectricity at room temperature have been investigated. The following research results are obtained ;1.Electric-field-induced magnetization reduction and the mechanism in oxides exhibiting simultaneously ferromagnetism and ferroelectrics.(1)Coexistence of ferromagnetism and ferroelectricity observed in La, Mn : BaTiO_3 and BaTiO_3-LaMnO_3 composites are due to a small amount of ferromagnetic (La, Ba)MnO_3 phase precipitated into the grain boundaries or the inside of the ferroelectric grains.(2)The composites BaTiO_3-LaMnO_3 are materials simultaneously exhibiting ferroelectricity and a relatively ferromagnetic magnetization at room temperature. The density and dielectric properties of the composites markedly improved with the grain size of LaMnO_3 decreasing. When an electric field of 750 V/mm was applied to the composites, magnetization reduction as large as 25 % was observed for the … More first time.(3)An electric-field-induced magnetization reduction similar to that in the composites was observed for BaTiO_3/BaTiO_3-LaMnO_3 composite / BaTiO_3 structures where a composite was sandwiched between ferroelectric insulator BaTiO_3 layers. This suggests that the observed magnetization reduction is probably not due to thermal effect but intrinsic field-induced effect. Change of hole concentration in (La, Ba)MnO_3 induced by the dielectric polarization may be responsible for the magnetization reduction.(4)An electric-field-induced magnetization reduction of 2.2 % for the applied voltage of 4V was observed in a BaTiO_3/(La, Ba)MnO_3/BaTiO_3 layer structure. This is direct evidence showing the magnetization change to originate from the induced polarization.2.Search for new multiferroic materials(1)Pb(Zr, Ti)O_3-LaMnO_3 composites are new multiferroics with higher ferroelectric Curie temperature and larger polarization than BaTiO_3 system. It has been found for the first time that they exhibits a magnetization reduction as large as 30 % for a low applied electric field of 0.4 kV/mm at room temperature. Less