Temperature and field dependence of resistivities and anisotropy of layered manganites La\u2082\u208b\u2082\u2093Sr\u2081\u208a\u2082\u2093Mn\u2082O\u2087

In-plane \u3f1ab and out-of-plane \u3f1c resistivities of La1.2Sr1.8Mn2O7 and LaSr2Mn2O7 have been measured by a multiterminal technique. We focus on the effects that magnetic and charge ordering transitions have on the anisotropy \u3c3ab/\u3c3c which reflects the ratio of the phase coherence lengths in the respective directions. Both resistivities of La1.2Sr1.8Mn2O7 decrease dramatically below the Curie temperature TC 48 135 K. Anisotropy changes with temperature nonmonotonically and displays a peak close to TC. In LaSr2Mn2O7, \u3f1c and \u3f1ab display a broad peak close to the paramagnetic-antiferromagnetic transition temperature TN 48 165 K. The anisotropy exhibits an even more complex behavior than in La1.2Sr1.8Mn2O7, displaying a maximum at the charge ordering temperature and a minimum at TN.NRC publication: N