CAJ | 학술논문

本文采用溶胶-凝胶工艺并结合脉冲激光沉积技术,在Pt/Ti/SiO2/Si衬底上制备了Co/Co3 O4/PZT多铁复合薄膜.对复合薄膜的微结构和组分进行了表征,并系统研究了复合薄膜中的交换偏置效应及其对磁电耦合作用的影响.研究结果表明,复合薄膜在77 K具有明显的交换偏置效应,交换偏置场达到80 Oe,且交换偏置场及矫顽场均随温度降低而增大.当温度降低到10 K时,交换偏置场增至160 Oe. X射线光电子能谱(XPS)测试结果证实在Co和Co3 O4界面处存在约5 nm厚的CoO层,表明77 K下的交换偏置效应源自反铁磁的CoO层对Co的钉扎作用.观察到复合薄膜的电容-温度曲线随着外加磁场大小和方向的改变而呈现出规律性的变化,表明复合薄膜存在磁电耦合效应.进一步研究发现,在低温下复合薄膜呈现出各向异性的磁电容效应,与磁场大小和方向密切相关.复合薄膜的这种磁电耦合特性主要与复合体系的交换偏置效应及基于界面应力传递的磁电耦合作用有关,本文对其中的物理机理进行了详细讨论与分析.
본문채용용효-응효공예병결합맥충격광침적기술,재Pt/Ti/SiO2/Si츤저상제비료Co/Co3 O4/PZT다철복합박막.대복합박막적미결구화조분진행료표정,병계통연구료복합박막중적교환편치효응급기대자전우합작용적영향.연구결과표명,복합박막재77 K구유명현적교환편치효응,교환편치장체도80 Oe,차교환편치장급교완장균수온도강저이증대.당온도강저도10 K시,교환편치장증지160 Oe. X사선광전자능보(XPS)측시결과증실재Co화Co3 O4계면처존재약5 nm후적CoO층,표명77 K하적교환편치효응원자반철자적CoO층대Co적정찰작용.관찰도복합박막적전용-온도곡선수착외가자장대소화방향적개변이정현출규률성적변화,표명복합박막존재자전우합효응.진일보연구발현,재저온하복합박막정현출각향이성적자전용효응,여자장대소화방향밀절상관.복합박막적저충자전우합특성주요여복합체계적교환편치효응급기우계면응력전체적자전우합작용유관,본문대기중적물리궤리진행료상세토론여분석.
The multiferroic Co/Co3O4/PZT composite films are prepared on Pt/Ti/SiO2/Si wafers by sol-gel process combined with pulsed laser deposition method. The phase structures, microstructural topographies and element valence states of the composite films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectrum (XPS). The ferroelectric, electrical and magnetic properties as well as the magnetoelectric coupling behaviors are measured, and the exchange bias effect and its influence on the magnetoelectric coupling behavior of the composite film are studied systematically. The results show the composite films have well-defined ferroelectric hysteresis loops with a remanent polarization value of ～17 μC/cm2. The composite film exhibits evidently an exchange bias effect. Typically, a exchange bias field of ～80 Oe is observed at 77 K. Both the exchange bias field and magnetic coercive field increase with reducing the temperature. The exchange bias field increases to 160 Oe when the temperature decreases to 10 K. The XPS results confirm that an about 5 nm-thick CoO layer appears at the Co/Co3O4 interface due to the oxygen diffusion during the preparation, indicating that the exchange bias effect at 77 K is caused by the pinning effect of the antiferromagnetic CoO layer while the exchange bias effect at 10 K originates from the combining effect of antiferromagnetic CoO and Co3O4 layers. The measurement results of magnetocapacitance versus magnetic field curves at different temperatures show that the composite films have remarkable magnetoelectric coupling properties. The response of capacitance to temperature changes with the variation of external magnetic field. Further investigations show that the composite film possesses distinct anisotropic magnetocapacitance effect. When the direction of the magnetic field changes, the magnetocapacitance of the composite film changes from positive value to negative value. Moreover, the magnetocapacitance value changes with the variations of temperature and magnetic field magnitude. Typically, at 300 K a maximum value of positive magnetocapacitance (5.49%) and a minimum value of negative magnetocapacitance of (1.85%) are obtained at ?4000 and 4000 kOe, respectively. When the temperature is reduced to 10 K, the positive magnetocapacitance decreases to a minimum value (0.64%) while the negative magnetocapacitance increases to a maximum value (5.4%). We perform a detailed analysis on such a magnetoelectric coupling behavior, and elucidate its origin, which should be attributed to the exchange bias effect and interface-mediated magnetism-stress-electricity coupling process.