Dramatic change in magnetization behaviors of la_1.4Sr _1.6Mn₂O_7+δ by control of excess oxygen

Effects of excess oxygen on the magnetic properties and crystal structure of La_1.4Sr_1.6Mn₂O_y, single crystals have been systematically investigated. The magnetic easy axis of the crystal annealed at 700°C in flowing oxygen for long time was discovered to change from the c-axis to the ab-plane below ferromagnetic transition temperature (T_C) by introduction of excess oxygen. Powder X-ray diffraction (XRD) analyses revealed that the c-axis length decreased and the a-axis length increased with increase of the excess oxygen. These behaviors are similar to that of increasing of strontium substitution level in the L _2-2xSr_1-2xMn₂O₇ [(La,Sr)Mn327] system. T_C was increased up to ∼130K by the introduction of excess oxygen, however the transition was broad. These suggested that the excess oxygen can play an important role for determining magnetic properties of the (La,Sr)Mn327.