RESUMO
The interplay between the crystalline and magnetic structures of a 4% Cr-doped Bi(0.37)Ca(0.63)Mn(0.96)Cr(0.04)O(2.99) has been investigated by alternating current (ac) magnetic susceptibility, electrical resistivity, and neutron diffraction measurements. The compound crystallizes into a monoclinic P2(1)/m symmetry. A Jahn-Teller distortion occurs at 280 K. The thermal behavior of charge transport may be described by a three-dimensional variable range hopping conduction. Strong interplay between the localized magnetic electrons and the itinerant electrons are clearly revealed as the localization length increases by 20% when the Mn spins become ordered below 85 K. Short range magnetic correlations persist up to 160 K. The collinear magnetic structure can be viewed as consisting of ferromagnetic spin-trimers antiferromagnetically embedded in a ferromagnetic environment. Cr-doping reduces the charge ordering temperature and the magnetic ordering temperature. It nevertheless introduces long-range ferromagnetism.
RESUMO
Magnetic susceptibility, x-ray diffraction, neutron diffraction and Raman scattering measurements are employed to study the effects of La substitution on the magnetic properties of multiferroic HoMn(2)O(5). 9% and 18% La-substituted compounds crystallize into the same orthorhombic Pbam symmetry as the parent compound. The magnetic responses to an ac driving magnetic field between 40 and 140 K are greatly enhanced by 18% La substitution. The neutron magnetic diffraction patterns reveal the development of short range magnetic correlations below 140 K. In addition, two Raman peaks and a series of new x-ray diffraction peaks suddenly develop below this temperature. Incommensurate long range antiferromagnetic order appears below 38 K. Magnetic frustration could be the main mechanism governing the present observations.
