Electronic Transport And Magnetic Properties Of Bi_2-xCr_xTe₃/PMN-PT And SrIrO₃/PMN-PT Heterostructures

Along with the accelerated process of device miniaturization,demand diversification and the artificial intelligence,the traditional single function materials,such as semiconductors,ferroelectric and ferromagnetic materials,et,all,have been increasingly unable to meet the needs of social development.As a result,the multifunctionalmaterialshavebeensignificantlycrucialtothe scientific-technological advancement and social development.Based on the research of traditional multiferroic materials,the design of thin film/ferroelectric single crystal heterostructrues has made the research field expanded from the previously pure magnetoelectrics properties to the electrical,optical,thermal and mechanical properties,etc.On the other hand,the discovery and research of novel materials,such as topological insulator materials and perovskite compounds with strong spin-orbit coupling effect,have brought great application prospect in the development of multiferroic,low-energy-consumption high speed transistors,spin electronics devices,etc.Based on the above background,in order to explore the new multi-function devices,the?1-x?PbMg_1/3Nb_2/3O₃-xPbTiO₃?PMN-PT?single crystal with excellent ferroelectric and piezoelectric properties were chose as the ferroelectric single crystal substrates.The Bi_2-xCr_xTe₃/PMN-PT?111?heterostructrues and SrIr O₃/PMN-PT?001?heterostructrues were obtained by growing Bi_2-xCr_xTe₃?x=0,0.07,0.14?thin film and SrIrO₃ thin film on PMN-PT substrates respectively.The following are the two main research works:?1??00l?oriented Bi_1.86Cr_0.14Te₃?BCT014?films with different thicknesses?6,24,and 48 nm?and 6 nm Bi_2-xCr_xTe₃?x=0,0.07?films were grown on PMN-PT?111?single crystal substrates via pulse laser deposition?PLD?.By applying bipolar electric field along the direction of the thickness of the substrates,we investigated the effect of ferroelectric of polarization upon the electrical transport properties of the films.The results illustrate that there,at the interface of BCT014/PMN-PT?111?heterostructrues structure,exits interfacial charge effect?or ferroelectric field effect?,resulting in carrier accumulation/depletion in the films without strain state changes,and a dynamic,reversible,and non-volatile modification of electrical transport and magnetotransport of BCT014 film was achieved.By which,modulation of the Fermi level of BCT014 film can be realized.For example,the metal-insulator transition of 6nm BCT014 film was observed by polarization switching.At the same time,using 2D Dirac model,we well explained the behavior of resistance at low temperatur.Considering the contribution of bulk carrier,a new model was given,which can better describe the resistance behavior at higher temperature and magnetic field.Again,using the interfacial charge effect,we realized the electric-field-induced surface state and inelastic scattering of the bulk state modulation of topological thin film.?2?SrIrO₃ thin films with different thicknesses?15,30,60,120 and 180 nm?were epitaxilly grown on the PMN-PT?001?single substrates by pulsed laser deposition?PLD?.We applied electric fields on the substrates across the film thickness direction to study the effects of the initial ferroelectric poling,polarization reversal,converse piezoelectric effect and electric-field-induced structural phase transition on the film lattice strain,electronic transport and magnetotransport.The results show that the poling-induced lattice strain effect plays a dominant role in changing the physical properties of the SrIr O₃ thin films at room temperature.At the same time,we also observed that the lattice strain effect has an effect on the magnetoresistance at low temperature.Using the structural phase transition of substrate at high temperature,we explained the sharp drop of resistance.