【作者】 吴海霞；

【导师】 姚素薇；

【作者基本信息】 天津大学 ， 应用化学， 2005， 硕士

【摘要】 本论文前一部分采用控电位双脉冲技术,在P型单晶硅(111)面上电沉积制备了一系列的[Co(1.5nm)/Cu(t)]100(0.9nm<t<4.5nm)多层膜。采用四探针法测试了Co/Cu多层膜的巨磁电阻(GMR)性能。研究发现镀液中添加微量的CrO3能显著提高多层膜的巨磁电阻值。选取不同铜层厚度的多层膜进行真空退火处理,当铜层较薄时,退火后多层膜的GMR值迅速降低,而退火对Cu层较厚样品的GMR值的影响要较为复杂,这被认为是出现了Cu-Co颗粒膜结构。本论文后一部分采用恒流电沉积方法,接着在半导体硅片上制备不同组分的Cu-Co颗粒膜,并对其进行高温退火处理。制备态各样品的巨磁电阻值均比较小。正交实验得出450℃为最佳退火温度,最佳退火时间为一小时。颗粒膜巨磁电阻值随Co浓度呈现出先增大后减小的趋势,当镀层组成为Co20Cu80时,450℃退火后得到最大巨磁电阻值为8.21%。当Co浓度大于40%后,由于阈渗效应,GMR值急剧降低。XRD测试结果表明,在研究的钴浓度范围内,制备态样品形成了单相亚稳态面心立方结构,并以(111)面为择优生长面,当镀层组成为Cu80Co20时,(111)面的择优取向系数达到最大。制备态样品的晶格常数随Co浓度的增大近似遵循线性规律变化。随着退火温度的升高,样品的晶面间距和晶格常数逐渐增大。600℃退火后样品的XRD谱图中开始出现金属Co的衍射峰,700℃退火后(111)和(200)面分别分离成单金属Cu和单金属Co的衍射峰,相分离完全。700℃退火后Co20Cu80样品的TEM测试得出:SAED结果为一系列的衍射环,表明薄膜为多晶结构; 暗场像图中得到析出的金属Co颗粒镶嵌于薄膜中,颗粒平均尺寸为5-20nm。制备态Co20Cu80样品的磁滞回线接近于超顺磁性物质的磁滞回线,随着退火温度的升高,样品的矫顽力、剩余磁化强度、饱和磁化强度等参数逐渐增大,发生了从超顺磁性到铁磁性的转变。对磁化强度的计算结果也证实了退火过程中发生的变化。更多还原

【Abstract】 A series of [Co(1.5nm)/Cu(t)]100(0.9nm<t<4.5nm) multilayers were deposited directly onto p-type Si substrates by double pulse-electrodeposition under potential control in the former part of the paper. Giant magnetoresistance (GMR) of Cu/Co multilayers was measured by four-point probe technique. It was found that GMR of the multilayers improved significantly with small amount of CrO3 added to the electrolyte. The multilayers with t=1.5nm、2.3nm and 3.5nm were selected to be vacuum annealed one hour at 200℃ and 300℃.When the Cu sublayer is very thin, the annealing process reduce the MR ratio dramatically. However, the influence on multilayers with larger Cu thickness is complicated, which is ascribed to the presence of Cu-Co granular films after annealing. Cu-Co granular alloys with different Co content were electrodeposited onto Si substrates by galvanostatic mode in the latter part of the paper, and subjected to high temperature annealing. The values of GMR of the as-deposited films were small. The results of the orthogonal experiment revealed that 450℃ was the optimal annealing temperature and the optimal annealing time was found to be one hour. GMR increases first, and then decreases with the increase of Co content in the granular films. It was found that the maximun GMR value reach 8.21% for the Co20Cu80 film after annealing at 450℃ for one hour. The values of GMR decrease dramatically when the Co concentration x>0.40 can be explained by the percolation mechanism. The XRD result showed that the as-deposited films form metastable alloy structure and has the predominant orientation of (111) crystal plane in the studied Co concentration range. The orientation factor of (111) crystal plane reached maximum for the Co20Cu80 film. The fcc lattice parameterαof the single phase fcc alloy changed linearly with Co concentration. The plane distance and lattice parameter increased with annealing temperature. The diffraction peak of pure Co was first observed in the XRD spectrum of 600℃ annealed sample. The (111) and (200) peaks split into diffraction peak of pure Cu and pure Co in the diffractogram of the 700℃annealed sample, indicating phase separation occurred upon annealing. The structure of the 700℃ annealed Co20Cu80 film was characterized by TEM: the SAED result was found to be diffraction rings. The magnetic Co particles was found in the dark-field image and its in the range 5-20nm. The hysteresis loop of the as-deposited sample was close to superparamagnetic material. The value of coercivity(Hc), remanent magnetization(Mr), saturation magnetization(Ms) increased with annealing, indicating the change from superparamagnetic to ferromagnetic contribution to the GMR effect. The calculation result of magnetization also verified this change.更多还原