【作者】 童俊军；

【导师】 刘秋香；

【作者基本信息】 广东工业大学 ， 材料物理与化学， 2011， 硕士

【摘要】 铁氧体是一种磁性材料,具有独特的高电阻率和良好的高频特性,被广泛应用在电子、信息、机械等工业领域中,随着电子器件向高性能化和尺寸微型化方向的发展,铁氧体材料受到越来越多的关注,并且已成为当前磁性材料领域研究和开发的重点。NiFe2O4 (NFO)是一种具有多功能用途的铁氧体材料,BaTiO3 (BTO)是一种典型的铁电材料,其在电调谐微波器件有巨大的应用前景。本文首先采用传统高温固相反应法成功制备了0.45NFO-0.55BTO复合陶瓷。利用复阻抗方法,测试频率从20Hz到2MHz,测试温度为348K至473K,系统地研究了样品的电性能,通过Cole-Cole图,计算了样品的晶粒、晶界电阻值和弛豫时间常数。结果表明,样品的自由电子浓度随温度升高而增加。利用直流电导率的Arrhenius曲线计算了晶粒和晶界的电导率激活能分别为0.32eV和0.38eV,存在这一激活能数值的主要原因是样品中氧空位的迁移,我们也发现弛豫特征频率随着温度升高而升高。另外,样品呈现了典型的磁化曲线,随着测试温度升高,饱和磁化强度(Ms)从2.38emu/g增加到3.13emu/g,矫顽力由0.20e增加到0.70e。然后我们采用射频磁控溅射法在Si(100)基片上分别制备了NFO薄膜(NFO/Si)和NiFe2O4/La0.7Sr0.3MnO3异质结(NFO/LSMO/Si),研究了LSMO缓冲层对NFO薄膜结构及磁性能的影响。经XRD和扫描电镜(SEM)测试,发现LSMO缓冲层有利于NFO薄膜沿(331)方向择优生长,制备的NFO薄膜的表面是很平整和均匀的。经磁性测试,当薄膜表面与磁场平行时,发现样品在室温下呈现出饱和的磁滞回线,当薄膜表面与磁场垂直时,没有发现任何磁化现象,这表明NFO薄膜平行于磁化方向时存在各向异性。从样品磁滞回线中可以看出,LSMO缓冲层有利于提高NFO薄膜的磁性能,其Ms由41.5 emu/cm3增加到350emu/cm3。我们也研究了溅射气氛对NFO薄膜结构与磁性能的影响。利用射频磁控溅射法在Si(100)基片上制备了NFO薄膜,溅射气氛包括纯Ar和Ar/O2混合气体。结果表明,在两种不同气氛中沉积的薄膜样品都呈立方尖晶石结构,通入少量氧气之后,薄膜择优取向发生改变,并且磁性能得到改善(Ms为41.5emu/cm3)。更多还原

【Abstract】 Ferrite materials are widely used in electronics, information, machinery and other industrial areas. Ferrite is a magnetic material has a unique high resistivity and good high frequency characteristics. Those properties have attracted considerable interest in recent years since they might offer the potential to enhance the performance or shrink the dimensional sizes of the microelectronic devices. At present, the ferrite materials are becoming an important research field of the magnetic materials. In the present work, NiFe2O4 (NFO) is one of the most versatile and technologically important ferrite materials. BaTiO3 (BTO) material is a typical ferroelectric material, so it has great application prospect in the electric tuning microwave components.The standard double sintering ceramic method was used to prepare the 0.45NFO-0.55BTO composite ceramic. Complex impedance spectroscopy of 0.45NFO-0.55BTO composite ceramic on the electrical characteristics were studied. The grain resistance, grain boundary resistance and relaxation time constant were calculated from the Cole-Cole plot. Impedance spectroscopy measurements were conducted in a frequency range from 20 Hz to 2 MHz and in a temperature range from 348 to 473 K. The impedance measurements have also shown the evidence of grain boundary conduction and lowering of barrier to the motion of charge carriers with rise in temperature. Using the Arrhenius plot of dc conductivity, the corresponding activation energy for both grain and grain boundary were 0.32 eV and 0.38 eV, respectively. The values revealed that the composite ceramic was attributed to the motion of oxygen vacancies within the bulk. We also found that the relaxation frequency shift to high side with increase in temperature. In addition, the sample exhibits hysteresis loop typical of magnetic behavior. The saturation magnetization increases from 2.38 to 3.13 emu/g and the coercivity increases from 0.2 to 0.7 Oe with increasing temperature.Nickel ferrite NiFe2O4 (NFO) thin films have been prepared on Si substrate (NFO/Si) and on La0.7Sr0.3MnO3 (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) revealed that the high (331)-oriented NFO films were grown on LSMO/Si substrate with smooth surface and cross-section morphologies. The samples show a clear hysteresis loop with in-plane H the magnetization. However, both samples do not show any hysteresis with the magnetic field applied perpendicular to the films plane, which indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the films plane. Study of magnetization hysteresis loop measurements reflects that LSMO buffer layer may improve the magnetic properties of NFO thin films, and the saturation magnetization increases from 41.5 to 350 emu/cm3.We also explored the influence of different growth atmosphere to the structure and properties of NFO films. NFO thin films on Si (100) substrate have been prepared by RF magnetron sputtering. The growth atmosphere consisted either of pure Ar or of a Ar/O2 mixture. The results show that both of the films deposited by two kinds of atmospheres exhibit spinel structure, and the preferential orientation changes when adding some oxygen. In addition, it is found that the magnetic properties of the deposited NFO films with oxygen are significantly improved(MS=41.5 emu/cm3).更多还原