The Preparation And Magnetoelectric Effect Of YIG/PZT-based Magnetoelectric Composite Materials

With the growing demand for next-generation light,compact,high-efficiency and energy-saving magnetoelectric（ME）multifunctional components,exploring new ME materials with stronger ME effect,lower power consumption,multifunction and integration capability has attracted a lot of interests.The ME composites composed of a magnetostrictive（piezomagnetic）and a piezoelectric（electrostrictive）material have been widely concerned for diverse potential applications in magnetic field（H）sensors,spintronics,ME memory and microwave devices,due to the advanced functionality of independent optimization of both phases and the allowance of room temperature operation.In particular,achieving a same degree of magnetic controllability using an electric field（E）is potentially faster process and involves lower energy consumption.Y₃Fe₅O₁₂（YIG）has been widely used as the magnetic phase in ME composites for the study of electric field-controlled ferromagnetic resonance（FMR）,magnetic anisotropy,magnetoresistance,and the non-volatile magnetization switching behavior,thanks to its small magnetic anisotropy,low loss in microwave frequency,and narrow FMR linewidth（?H）.The ferroelectric materials to be bonded to YIG include BST,PZT and PMN-PZT.In particular,PZT and PMN-PZT have gained special attention because of their good piezoelectricity.However,the YIG films are always micrometer thick and the epoxy as the bonding layer will weaken inevitably the ME effect.In order to enhance the elastic coupling,and to fit the novel light and integrated ME devices,the first systems proposed in this paper are PZT/YIG composite films on SiO₂/Si substrates.The preparation and properties of YIG and PZT are optimized firstly,then the converse ME（CME）performances can be examined.In order to realize the E-field tuning of the magnetization（M）of YIG film,and to eliminate the effects of clamp and leakage,the second systems are YIG film/PMN-PZT ceramic quasi-2-2 ME composites.The main research results of this paper are as follows:1.Preparation of crack-free YIG films with excellent properties on SiO₂/Si.（1）YIG films were deposited on SiO₂/Si substrates by RF magnetron sputtering,the annealing parameters dependencies of microstructures and magnetic properties of YIG films were presented.When the annealing temperature is 750°C and the cooling rate is 1°C/min,uniform and crack-free YIG films can be obtained.（2）The effects of Ar pressure on the composition and magnetic properties of YIG films were studied.When the pressure is 0.55 Pa,the obtained crack-free YIG films fit the stoichiometric ratio of Y₃Fe₅O₁₂,the saturation magnetization（M_s）is 1.35 kG,coercive field is as low as 9.76 Oe.The narrow?H of 5.18 mT predicts the possibility for further reduction of the magnetic loss in YIG film-based microwave devices.2.Preparation of oriented Pb(Zr_0.53Ti_0.47)O₃ films with excellent performances.The infulences of bottom electrodes（LNO/Pt,LNO）and film thickness on the electrical properties of PZT film were investigated.The 480 nm-thick PZT films have the best ferroelectric,piezoelectric and dielectric properties.Especially on LNO,the PZT films have good electrical properties:the saturation polarization(P_max)is 53.36μC/cm²,piezoelectric coefficient(d₃₃)is 83.14 pm/V,the maximum dielectric constant is 955（@39 kV/cm）,dielectric tunability is 60.74%（@245 kV/cm）,they also have lower coercive field（73.35 kV/cm）and dielectric loss(2.4⁷.7×10^-4)than those on LNO/Pt.Therefore,LNO is the preferred bottom electrode for ME composite films.3.Fabrication and performances of the low-loss PZT/YIG ME composite films.Pt/PZT/LNO/YIG/SiO₂/Si composite films fabricated by using the optimized preparation process of YIG and PZT films maintain the good magnetic and electric properties of each phase:the M_s is kept as 1.38 kG,P_max is as high as 43.47μC/cm²,and the d₃₃ is 74.84 pm/V.The?H of the composite film is similar to that of the single-layer YIG film,and it is about 10 mT when the H-field is parallel to the film.4.Fabrication and ME effect of YIG/PMN-PZT ME composite systems.（1）The E-field tuning of M,and the impact of the YIG film magnetic state on strain-modulated CME effect were studied.The strain originated from ceramics can modulate the film magnetic anisotropy,resulting in the magnetization difference.This difference will increase with the decrease of the bias H-field.Both the strain-induced change of M(?M/M_0i)and the CME coupling coefficient（a）can reach their maxima at the Hc of YIG film(7.0%and 10.9×10^-8 s/m,respectively),even in the absence of an external H,there is still a large CME coefficient(5.6×10^-8 s/m).（2）The influence of the film thickness on the CME coupling was presented.For a certain thickness,the maximum a always occurs at the E_C of PMN-PZT（4.1 kV/cm）and the H_C（20 Oe）of YIG.For a certain bias H,a increases with the increase of the YIG thickness.The maximum a(3.1×10^-7 s/m)observed in 600 nm-thick YIG is 5times that obtained in the LSMO film/PMN-PT（001）single crystal system.