Observation of two magnetic transitions and conventional exchange bias effect in high dielectric iridate La2Cu0.9Mn0.1IrO6

Abstract

Magnetic insulators or semiconductors having high dielectric constant are a class of materials which are very promising from experimental perspective and thus have been extensively investigated herein. The multiple magnetic phases, observation of conventional exchange bias phenomenon and high dielectric constant in La2Cu0.9Mn0.1IrO6 double perovskite is reported. The incorporation of Mn (10%) into predominantly antiferromagnetic spin structure of La2CuIrO6 leads to mixed valence state of Mn (Mn2+ and Mn3+). We report here the observation of conventional exchange bias phenomenon and high dielectric constant in La2Cu0.9Mn0.1IrO6 double perovskite. The compound crystallizes in triclinic structure with P1‾ space group and undergoes two magnetic transitions at Néel temperature TN = 66 K and Curie temperature TC = 14 K respectively. Large value of conventional exchange bias (CEB) of 731 Oe for a bias cooling field of 50 kOe at T = 3 K is the major highlight. Analysis of the cooling field dependence on the exchange bias field and magnetization indicates the pinned or frozen ferromagnetic (FM) spins give rise to the unidirectional shift of the hysteresis loops known as the EB effect. The training effect has been interpreted using spin frozen and spin flipping model. Dielectric constant reveals a step like increase from low temperature (T < 90 K) value of ∼ 45 to colossal value of ∼ 5350 at high temperature (T ∼280 K).