Transport, magnetic and thermal properties of Pr doped LaSr2Mn2O7: a Kondo-type behaviour of resistivity

Abstract

The interplay of spin, charge and lattice degrees of freedom in LaSr2Mn2O7 (tetragonal, space group I4/mmm) yields a variety of properties such as a CE-type charge ordering and an A-type spin ordering. We have studied the effect of partial replacement of La by Pr on the magnetic and thermal properties of this system. Compounds of the type La1-xPrxSr2Mn2O7 (0 <= x <= 1) have been prepared and are found to crystallize in the same tetragonal structure. Magnetization, electrical resistivity and specific heat measurements have been carried out on these compounds. Replacing La by Pr in this system affects both the electronic and the magnetic state of the system. It is observed that the charge ordering temperature and the net magnetic moment reduce with the incorporation of Pr in the lattice. In the antiferromagnetic state, the charge carriers in La1-xPrxSr2Mn2O7 behave like a weakly scattered two-dimensional gas whose resistivity (rho) is a logarithmic function of temperature, T (rho proportional to log T), over a certain temperature interval. This behaviour is enhanced with increasing concentration of Pr in the samples and is proposed to originate from quantum interference. The electronic part of the specific heat shows the presence of the two transitions at T-CO and T-N and a contribution from antiferromagnetic magnons at low temperatures.