Ferromagnetic domain structures in Al-substituted La_1-xSr_xMnO₃

Abstract

Ferromagnetic (FM) domain structures in double-exchange manganites La_1-xSr_xMnO₃ (x=0.175, 0.30) were investigated by low-temperature Lorentz transmission electron microscopy (TEM). It was found that the rhombohedral-to-orthorhombic transition around 185 K in La_0.825Sr_0.175MnO₃ accompanies drastic change from large FM domains with the 1 μm size to the 100 nm sized FM one with the stripe pattern. By partial substitution of non-magnetic Al ion for Mn one, the FM domain structures with the straightforward stripe pattern in the orthorhombic phase of La_0.825Sr_0.175MnO₃ changed into the FM domains with the wavy stripe pattern and, in addition, some defects such as the dislocation were often observed. On the other hand, no changes of the FM domain structures were found by partial substitution in the rhombohedral phase of La_0.7Sr_0.3MnO₃.