Magnetization reversal and sign reversal exchange bias field in polycrystalline Ni5.33Ta0.67B2O10

The sign reversal of both magnetization and exchange bias field was studied in the polycrystalline Ni5.33Ta0.67B2O10. The crystal structure of Ni5.33Ta0.67B2O10 is quasi–low dimensional due to NiO6/TaO6 octahedra forming two dimensional infinite layers. The antiferromagnetic/ferrimagnetic phase transition was observed at TN = 165 K. The negative exchange bias effect was found in the 30–90 K temperature range, whereas the positive exchange bias effect was observed at temperatures below 30 K. We assume that the exchange bias effect is due to different types of magnetic ordering of Ni2+ magnetic moments in two layers.