The negative magnetization and dielectric relaxation in (La0.3Pr0.7)1-xCaxCrO3 ceramics

The (La 0.3 Pr 0.7 ) 1- x Ca x CrO 3 ( x  = 0, 0.1, 0.3 and 0.5) ceramics have been synthesized by a sol-gel method. The compounds crystalize in orthorhombic structure with space group Pnma at room temperature . The magnetic measurements confirm that the materials form canted antiferromagnetic (AFM) ordering from 254.1, 231.2, 118.5, 49.3 K for the samples of x  = 0, 0.1, 0.3 and 0.5, accompanied by a spin reorientation transition at 191.4, 145.1, 55.8, 38.9 K because of the Pr 3+ -Cr 3+ interaction. Meanwhile, a positive exchange bias effect is observed due to the antiparallel coupling between the Pr 3+ and the canted AFM structure of Cr 3+ . The Néel temperature , compensation temperature as well as the coupling strength of Pr 3+ -Cr 3+ monotonously decrease with the increase of Ca 2+ concentration. For the samples of x  = 0.1 and 0.3, there exists a field induced Pr 3+ -Pr 3+ AFM ordering. By means of dielectric measurements, large permittivity at room temperature and dielectric relaxation are observed in all the samples. The permittivity is decreased and dielectric relaxation moves to low temperature range with the increase of Ca 2+ concentration. A relaxor-like ferroelectric transition is observed in the measuring temperature range in Ca 2+ doped samples.