The effect of high temperature annealing on the antisite defects in ferromagnetic La2NiMnO6 double perovskite

The ferromagnetic properties of the double perovskite La2NiMnO6 are governed by the Ni2+-O2--Mn4+ superexchange interaction. The Ni2+ and Mn4+ valence states along with the antisite disorder strongly influence the magnetic interactions in the compound. Here, we report on the effect of high temperature annealing on the antisite disorder and related properties of La2NiMnO6. X-ray absorption measurements reveal nominal changes in the local environment around B/B' sites of all samples. However, saturation magnetization decreases due to increased antisite disorder, which enhances the Ni2+-O2--Ni2+ and Mn4+-O2--Mn4+ antiferromagnetic exchange interactions. At 5 K, a large saturation moment of similar to 4.95 mu(B)/f.u is observed for the sample annealed at 950 degrees C. For all samples, the ferromagnetic-paramagnetic transition is observed at 280 K, which is attributed to the fact that the Ni-Mn interatomic distance remains constant for all the samples. Our study suggests that the Ni/Mn valency and Curie temperature are insensitive to the antisite disorder present in the system.