Low-energy spin-wave excitations in the bilayered magnetic manganite La2-2xSr1+2xMn2O7 (0.30≤x≤0.50) -: art. no. 214428

We have studied the low-temperature behavior of the magnetization and specific heat of the bilayered perovskite system La2-2xSr1+2xMn2O7 for 0.30less than or equal toxless than or equal to0.50. Our analysis reveals that below 30 K the temperature dependence of the magnetization of the ferromagnetic samples, x=0.30, 0.32, and 0.36, in a field of 1 T can be interpreted in terms of the thermal excitations of a two-dimensional gas of ferromagnetic magnons. The specific heat in zero field for these samples, such as for the x=0.50 antiferromagnetic one, is linear with temperature in the range of 1.8 K less than or equal toTless than or equal to10 K. This behavior can be also explained by the magnon gas model. By comparing specific heat measurements in zero field with those taken in a field of 9 T we are able to extract the lattice and electronic contributions and determine the in-plane exchange interactions. They are found to be in reasonable agreement with the values inferred from analysis of the magnetization data and also with the values reported by inelastic neutron scattering studies. In addition, we found that the electronic density of states obtained for the x=0.50 sample is in agreement with previous band structure calculations.