Magnetic anisotropy and domain structure of the layered manganite La1.36Sr1.64Mn2O7

The magnetic anisotropy and domain structure of La1.36Sr1.64Mn2O7 were investigated using magneto-optical imaging and magnetization measurements. First and second order anisotropy constants of K1=2.5x105 erg/cm3 and K2=2.8x105 erg/cm3 at 20 K are obtained. With increasing temperature K1 and K2 drop rapidly until K1 changes sign near 80 K. A model of near cancellation of a strong single-ion anisotropy (ku≅0.7x106erg/cm3 at 20 K) and large dipolar effects originating from the layered structure can account for the observed anisotropy. Below 75 K a well developed maze shaped domain pattern with 10 μm domain width is observed which shows signatures of domain branching and flux closure typical for a moderately anisotropic uniaxial magnet