Electronic Structure, Phonons and Dielectric Anomaly in Ferromagnetic   Insulating Double Perovskite La2NiMnO6
  Using first-principles density functional calculations, we study the electronic and magnetic properties of ferromagnetic insulating double-perovskite compound La2NiMnO6, which has been reported to exhibit interesting magnetic field sensitive dielectric anomaly as a function of temperature. Our study reveals existence of very soft infra-red active phonons that couple strongly with spins at the Ni and Mn sites through modification of the super-exchange interaction. We suggest that these modes are the origin for observed dielectric anomaly in La2NiMnO6. 
Hena Das, Umesh V. Waghmare, T. Saha-Dasgupta and D. D. Sarma