Structure,electrical And Magnetic Properties Of Aurivillius Bi₅Ti₃FeO₁₅ Thin Films Modulated By Mn Doping

The bismuth layered materials with Aurivillius phase structure have strong ferroelectric properties,great piezoelectric properties,high Curie point and anti-fatigue properties.More importantly,the new physical phenomenon in these materials caused by the coupling between different physical order parameters,such as force,magnetic and polarization,which make bismuth layered materials have widely potential applications for sensors,microwave equipments,data storage,optoelectronic technology and so on.Bi₅Ti₃FeO₁₅?BTFO?is a typical bimuth layered material system,Besides its characteristics of Aurivillius phase,it exhibits the characteristics of ferroelectric and magnetic coexistence,as well as the coupling between these orders.However,its magnetic property is antiferromagnetic,which has low transition temperature and weak magnetoelectricity,so the current research of BTFO system mainly focuses on this property.There are many researches show that the element doping is a very effective method,which can modulate and modify the properties of materials.The effect of a series of different Mn-doping concentrations on structures,electrical and magnetic properties,and domain structure,especially on the modulation of magnetic properties,were systematically studied by doping.Based on this,we give the main research contents and results as follows.We prepared BTFO films with different Mn doping concentration by chemical solution deposition.The general formula of the structure is Bi₅Ti₃Fe_1-xMn_xO₁₅?BTFMO,where x=0.05,0.1,0.15,0.2,0.25,0.3,0.4?.We systematically studied the microstructures,crystal structures,electrical properties,domain switching and magnetic properties of these BTFO thin films,and the results show that Mn doping does not change the Aurivillius phase structure of BTFO system,but Mn doping contributes to the growth of BTFO film grain.We found that Mn doping can enhance the ferroelectric and dielectric properties of BTFO system,but there is a doping limit.When the Mn doping concentration is0.25,the ferroelectric and dielectric properties of the system are the best,the remanent polarization?P_r?can reach 17.2?C/cm²,and the relative dielectric constant??_r?can reach 371.2 at 10 kHz.However,with the further increase of Mn,the ferroelectric and dielectric properties begin to deteriorate,and dielectric relaxation occurs at low frequencies,indicating that Mn doping introduces more oxygen defects.In addition,it is found that the doping limit also exists in the leakage current,leakage current increases dramatically at high concentrations.Furthermore,we studied the mechanism of leakage.We found that Schottky emission,SCLC and PF emission mechanisms work together at low doping concentration,and ohmic conductivity mechanism at high doping concentration.We found that Mn doping can modulate the magnetic sequence of BTFO materials with these all films show ferromagnetism.Mn doping can also increase the remanent magnetization of BTFO materials,which indicates the superexchange effect in the materials.We researched the domain structure of BTFO thin films,and found that all Mn-doped samples exhibits 0 ^o and 180 ^o domain,indicating that the ferroelectric polarization in films.By the way of voltage test,we achieved the 180 ^o domain reversal.