[Show abstract][Hide abstract] ABSTRACT: We have investigated magnetic, electrical, and thermal transport properties (Seebeck effect and thermal conductivity) of LaSr2Mn2−yCryO7 polycrystalline samples (y=0.1, 0.2, 0.4, and 0.6). The Cr3+ substitution for Mn3+ sites causes a removal of dx2−y2 orbital of eg electron, resulting in a volume shrinkage of the lattice. Magnetic measurements reveal the appearance of a glassy behavior for Cr-doped samples, accompanied by both a collapse of the A-type antiferromagnetic structure and the growth of ferromagnetic clusters. Cr-doping effect on electrical transport strongly enhances an insulating behavior over a wide range of temperatures, while it suppresses a local minimum of thermoelectric power at lower temperatures. For all polycrystalline samples with Cr substitution, the variable-range-hopping conduction model gives a reasonable fit to both resistivities and Seebeck coefficients. The phonon thermal conduction gradually rises with increasing Cr content, which is in contrast to a typical impurity effect on thermal conductivity. We attribute this to a suppression of local lattice distortion through the introduction of Jahn-Teller inactive ions of Cr3+.
[Show abstract][Hide abstract] ABSTRACT: We have carried out thermoelectric power (S), magnetization and
magnetoresistance measurements on
(y=0.1, 0.2 and 0.4). In the bilayer manganite
LaSr2Mn2O7 (hole doping level x=1/2),
it is well known that the coexistence of metallic A-type
antiferromagnetic (AF) phase and CE-type charge/orbital order (CO/OO)
phase is essential to understand physical properties. The Cr-doping
strongly suppressed the AF transition temperature and its associated
peak in S down to lower temperatures. The Cr impurities on the Mn site
in the bilayer manganite system did not cause such a dramatic influence
as the insulator to metal transition in cubic manganites. This finding
is discussed on the basis of phase separation model concerning the
A-type majority and CE-type minority phases.