Electric field dependences of Curie and Neel phase transition temperatures in magnetoelectric relaxor multiferroic Pb(Fe0.5Ta0.5)O3 crystals seen via acoustic emission

Pb(Fe0.5Ta0.5)O-3 magnetic and ferroelectric relaxor multiferroic crystals have been studied under both temperature and dc external electric field conditions by means of acoustic emission technique. All the characteristic relaxor points as Burns T-d approximate to 610K and intermediate T*approximate to 500K temperatures, as well as both Curie ferroelectric cubic-tetragonal T-c1 approximate to 259K and tetragonal-monoclinic T-c2 approximate to 201K structural and Neel antiferromagnetic-paramagnetic T-N approximate to 187K phase transitions have been successfully detected. It is shown that, when an external dc electric field is applied, both T-c1 and T-c2 exhibit a nonlinear or V-shape behavior and attain the sharp minima at threshold temperatures T-th1 approximate to 247K and T-th2 approximate to 200K with the threshold field E-th approximate to 0.1kVcm(-1), as the field enhances, while their acoustic emission count rate monotonically increases. It is shown, too, that the T-N behaves linearly in dependence on dc electric field with a negative slope of about -20KcmkV(-1), while its acoustic emission count rate monotonically decreases. All these data are discussed from a viewpoint of presence of polar nanoregions and magnetoelectric coupling effect in Pb(Fe0.5Ta0.5)O-3 crystals.