【作者】 马垒；

【导师】 钟夏平； 曾德长； 刘仲武；

【作者基本信息】 华南理工大学 ， 材料加工工程， 2011， 博士

【摘要】 铁磁性金属纳米颗粒薄膜系统中存在的巨磁电阻效应、巨霍尔效应、高矫顽力效应等新特性,使其在磁性传感器件、高密度记录介质、读出磁头和磁性随机存取存储器等研究领域具有广阔的应用前景。近年来,纳米金属磁性颗粒包埋在非磁性碳基体中的颗粒膜体系由于在高抗蚀性材料和巨磁阻材料方面具有潜在的应用价值,吸引了人们越来越多的注意。另外,具有有序结构的FePt和CoPt材料与非磁性成分形成的复合薄膜,在超高密度磁记录介质领域展示了诸多优越性也成为材料科学领域的研究热点。本文用直流磁控溅射法在Si（100）和载玻片衬底上制备了铁磁性金属-碳基（Co-C, Fe-C）颗粒膜和硬磁性的CoPt-C、FePt-SiN系列纳米颗粒薄膜,对它们的制备、结构、磁性质和输运特性进行了系统研究。主要得到了以下结果:1)在制备态的CoC薄膜中,Co和碳成分是以非晶结构存在,且该碳基薄膜为类金刚石（DLC）薄膜;制备态的CoC薄膜表面光滑,颗粒尺寸及膜厚度均匀,当Co含量为2.5 at.%时薄膜的粗糙度（Ra）为0.152 nm,纳米尺寸的Co颗粒均匀分布在碳基体中;Co成分掺入后sp²C的无序结构（D峰）和C=C键的E_2g伸缩振动峰（G峰）没有漂移,薄膜中sp³杂化碳的含量不变,Co的添加没有促进碳基薄膜的石墨化;Co_xC_1-x薄膜具有较好的软磁性能,矫顽力均不超过180 Oe;当Co掺入后,与非晶碳膜相比,Co_xC_1-x纳米复合薄膜显示了较高的磁电阻（MR）效应,当x=2.5 at.%,膜厚约为80 nm,外磁场垂直于膜面方向时,检测到的最大MR值为36%,随着膜厚和Co成分的增加,磁电阻值逐渐降低;磁电阻效应可以用p-n异质结和界面散射效应来解释。2)Fe掺杂的Fe_xC_1-x复合薄膜也为DLC膜,Fe和C也是以非晶形态存在,且Fe的加入使该膜的D峰和G峰向低值方向漂移,sp³杂化碳的成分增加;当Fe的加入量为18 at.%时,薄膜的表面粗糙度Ra为0.231 nm;Fe_xC_1-x纳米复合薄膜表现为软磁性能,矫顽力约为20 Oe;制备态的Fe_xC_1-x薄膜有较大的磁电阻效应,在300 K温度和5特斯拉（T）磁场下,Fe₁C₉₉薄膜的正磁电阻值达到93%;FeC复合薄膜中观察到的异常电输运现象遵循双通道导电模型,该模型能很好地和实验结果相吻合。3)制备态的CoPt-C薄膜是无序的面心立方（fcc）结构,在700℃热处理1h以后,转变为有序的面心四方（fct）结构,CoPt-C薄膜的相转变温度不低于700℃;制备态的CoPt-C样品表面平整、致密、均匀,颗粒尺寸约为23.5 nm,并随着碳含量的提高,颗粒尺寸逐渐减小,碳成分在细化晶粒方面起到了显著的效果;CoPt-C薄膜的饱和磁化强度（M_s）随C含量的增加先增加后减小,在C含量为15 at.%时,Ms约为1000 emu/cm³;C含量为35 at.%时能最大地提高薄膜的矫顽力（H_c）,在700℃热处理1小时后,膜面垂直磁场方面的最大矫顽力达到4200 Oe;首次发现用于磁记录介质的CoPt-C颗粒膜体系具有负磁电阻效应,MR的值在2T磁场下接近-1%。4)利用反应磁控溅射方法成功制备了具有包埋结构的FePtSiN薄膜;制备态的FePtSiN薄膜是由无序的A1-FePt相组成,在600℃热处理1小时之后,转化为有序的面心四方结构,且随着热处理温度的增加,有序相的衍射峰增强;随Si、N含量的不同,FePtSiN薄膜的晶格常数发生了相应的变化;加入合适比例的Si、N成分能有效促使Si-N相的形成,并从FePt合金中脱离出来均匀分布在FePt颗粒周围,起到隔离其交换耦合和限制晶粒长大双重作用;Si-N成分以非晶的形式存在于FePtSiN薄膜中;制备态的FePtSiN薄膜表现为fcc结构的软磁性能,矫顽力不高于20 Oe,当在700℃热处理1小时之后,室温下的矫顽力达到13.6 kOe,而100 K温度下的矫顽力高达17.5 kOe;FePtSiN复合薄膜的硬磁性机理和高矫顽力特性在很大程度上依靠Si-N的含量。更多还原

【Abstract】 Novel properties such as giant magnetoresistance （GMR）, giant Hall effect （GHE） and high coercivity have made ferromagnetic nanogranular films promising candidates for the applications of magnetic sensors, high density magnetic recording materials, read-out magnetic head and magnetic random access memory. Recently, magnetic granular films, consisting of nanoscale ferromagnetic grains dispersed in a non-magnetic carbon matrix, have received much attention due to their potential applications as high-resistive soft magnetic materials and giant magnetoresistance materials. In addition, L1₀ ordered FePt and CoPt films embedded in non-magnetic matrix have become the focuses in the field of ultra-high density magnetic recording medium and materials science.Various series of ferromagnetic nanocomposite films, including soft ferromagnetic carbon-based granular films （Co-C, Fe-C）, hard ferromagnetic CoPt-C and FePt-SiN granular films were fabricated on Si（100） or glass substrates by dc magnetron sputtering. Their preparation, structure, magnetic properties, and transport properties were studied systemically. The main results are as follows:Firstly, the cobalt and carbon or graphite in the as-deposited films are in amorphous state, and the Co_xC_1-x films are diamond like carbon （DLC） films. The Co_xC_1-x films have smooth surface （Ra=0.152nm）, homogeneous grain size and film thickness. The nano-sized amorphous Co particles were homogeneously dispersed in the amorphous cross-linked carbon matrix. After doping cobalt into DLC film, the sp³-hybridized carbon content in DLC composite films almost had no change. The coercivity of Co_xC_1-x film is less than 180 Oe. The as-deposited Co_xC_1-x granular films with 80nm thickness had larger value of magnetoresistance than the amorphous carbon film. A very high positive MR, up to 36% at magnetic field B=5 T and x=2.5 at.% was observed in a Co_xC_1-x granular film at room temperature when the external magnetic field was perpendicular to the electric current and the film surface. With increase of the film thickness and Co-doped content, the MR decreased gradually. The MR effect of the Co_xC_1-x granular films may be interpreted by p-n heterojunction theory and interface scattering effect.Secondly, as-deposited Fe-doped amorphous Fe_xC_1-x granular films are also in amorphous state, and the Fe_xC_1-x films are diamond like carbon （DLC） films. After doping iron into DLC film, the Fe_xC_1-x films have smooth surface morphology and the surface roughness Ra is 0.231nm for x=18 at.%. Moreover, the sp³-hybridized carbon content in DLC composite films increases with Fe doping. The Fe_xC_1-x films have good soft magnetic properties, the coercivity of only around 20 Oe was obtained. The as-deposited Fe_xC_1-x granular films with 160nm thickness have larger value of magnetoresistance. A very high positive MR, up to 93% with x=1 at.% was observed in a Fe_xC_1-x granular film at 300 K. The MR effect may be interpreted by two-channel electric conduction model. The model is in accordances with the experiment results.Thirdly, the CoPt in as-deposited CoPt-C films had face-centered cubic （fcc） structure, which transforms into the face-centered tetragonal （fct） structure after thermal annealing at 700°C. The as-deposited films have smooth surface morphology and the average grain size is about 23.5 nm. Carbon components have played important effect in grain refinement. The saturation magnetization increases firstly and then decreases with the increase of C concentration, about 1000 emu/cm3 with 15 at.% C. The coercivity of CoPt-C films is up to 4200 Oe measured at 300 K when the films are annealed at 700°C for 1h. It is the first time that the CoPt-C films exhibited negative MR effect about -1% at 2T.Finally, FePtSiN films consisting of FePt nanoparticles embedded in a Si-rich matrix were successfully fabricated on silicon substrate by dc reactive magnetron sputtering. The as-deposited films had fcc structure, which transforms into fct structure after thermal annealing at 600°C. The grain size of FePt increased with the annealing temperature but decreased with increasing Si-N content. Increasing Si content led to the formation of Si-N rich amorphous phase distributed between the FePt nano-grains, which reduced the lattice distortion and increased the coercivity. The fct-FePt films annealed at 700°C exhibited very high coercivity, up to 13.6 kOe at room temperature and about 17.5 kOe at 100 K. The high coercivity mechanism depends largely on Si-N concentration. These FePtSiN films with novel structure have shown promise for high density magnetic recording medium.更多还原