离子束溅射制备Co/Pt多层膜的结构和磁性

采用离子束溅射技术制备了Co／Pt多层膜，并研究了多层膜的结构和磁性随Co层厚度（tCo）或Pt层厚度（tPt）的变化关系。结果表明Co层呈现出hcp结构的（002）织构，Pt层表现出fcc结构的（111）织构。当Co层和Pt层都比较薄时，界面有Co-Pt的化合物形成。当tPt=2．4nm而tCo在0．6～2．4nm变化时，样品的磁矫顽力（Hc）随tCo增加而下降，饱和磁化强度（Ms）随tCo增加而增加。当tCo=1．2nm而tPt在1．2～4．8nm变化时，Hc呈现先升后降的变化，Ms随tPt增大而减小。样品的Hc还受调制周期（D）和周期数ny的影响，通过对Co层和Pt层的厚度比、调制周期、周期数的设计，可以获得较大的磁矫顽力。     

Pt/(Pt/Co)n/FeMn/Pt多层膜中Pt插层对交换偏置场的影响

在具有垂直磁各向异性Pt／（Pt／Co）n／FeMn／Pt多层膜中的Co／FeMn界面插入极薄的Pt层时，其交换偏置场有明显提高。研究结果表明：由于在Co／FeMn界面存在界面反应，破坏了（Pt／Co）n多层膜中靠近FeMn层的Co层的垂直磁各向异性，导致垂直交换偏置场Hex减弱。当在（Pt/Co）n与FeMn界面之间插入Pt层时可以有效地阻止这一反应发生，从而提高了多层膜的垂直交换偏置场Hex。     

颗粒合金膜Co20NixCu80-x巨磁电阻和磁性能

研究了用快淬制备的铸态和退火处理后的颗粒合金膜Co20NixCu80-x（0≤X≤20）的磁电阻和磁性能。与高Ni的样品相反的是，低Ni的样品在低温下AR／R上升。无论低Ni或高Ni样品的剩余磁化强度Mr和矫顽力Hc都随退火温度的上升而增加。     

类三明治结构C/Co/C纳米颗粒膜微结构和磁特性的研究

在室温下,用对靶磁控溅射法制备了系列类三明治结构C/Co/C颗粒膜.C靶和Co靶分别采用射频溅射和直流对靶溅射模式,并且随后进行了原位退火.用振动样品磁强计(VSM)和扫描探针显微镜(SPM)系统研究了C/Co/C颗粒膜的微结构和磁特性与磁性层厚度、非磁性层厚度、退火温度的关系.X射线衍射(XRD)图样显示出退火400℃的样品具有很好的六角密堆积结构.扫描探针显微镜图样和δM曲线说明Co纳米颗粒嵌在非晶质的C母基内.振动样品磁强计测量表明磁矩很好的排列在膜面内,随着磁性层Co层厚度的增加,矫顽力(Hc)先增大然后减小.在Co层厚度为20nm,C层厚度为30nm,退火温度400℃时,矫顽力达到最大值,剩磁比(S)接近于1.     

Pt的含量对[Fe/Pt]n多层膜磁性能的影响

采用射频磁控溅射的方法,在玻璃基片上制备了不同膜层结构的[Fe/Pt]n多层膜,经不同温度真空热处理后,得到L10有序结构的FePt薄膜.实验结果表明,[Fe/Pt]n多层膜结构可以有效降低FePt薄膜的有序化温度,350℃退火30min后其平行膜面矫顽力可达1.6×105A/m;多层膜结构中,Pt层厚度与Fe层厚度相同时,矫顽力最大,当Fe、Pt层厚度比偏离1:1时,在Fe/Pt接触处易产生Fe3Pt和FePt3软磁相;Pt层和Fe层厚度相等且总厚度相同的情况下,Fe、Pt单层厚度越薄,有序化温度越低,且对应的矫顽力大.     

CoSiB/Pt多层膜垂直磁各向异性及热稳定性

采用磁控溅射方法在单面附有300 nm SiO2的单晶硅基片上制备了以Pt为底层的CoSiB/Pt多层膜样品.CoSiB/Pt层周期数确定为2,对样品底层厚度及周期层厚度进行调制,根据反常霍尔效应系统地研究了CoSiB/Pt多层膜垂直磁各向异性(perpendicular magnetic anisotropy,PMA)及薄膜的热稳定性.通过对这些参数的调节获得了具有良好垂直磁各向异性的最佳多层膜样品结构Pt(1)/[CoSiB(0.5)/Pt(1)]2,底层Pt和周期层中CoSiB,Pt的最佳厚度分别为1,0.5 nm和1 nm.对最佳样品进行XRD图谱分析,磁滞回线测量以及一系列退火处理.结果表明,样品具有明显的(111)CoPt衍射峰,形成了较好的(111)织构,界面耦合增强,结晶度较好,计算出样品的有效磁各向异性常数Keff达到5.11×104 J·m-3,样品具有良好的PMA;当退火温度为200℃时,样品的CoPt(111)峰强度显著增强,界面形成了较强的(111)织构,Keff达到最大值1.0×105J·m-3,当退火温度不超过400℃时,样品仍能保持良好的PMA.多层膜样品结构Pt(1)/[CoSiB(0.5)/Pt(1)]2具有良好的PMA和热稳定性,且合适的退火温度有利于提高样品的PMA.     

非晶稀土——过渡金属磁光薄膜热稳定性研究

采用射频磁控溅射方法制备非晶ＤｙＦｅＣｏ磁光薄膜。样品的克尔回线、转矩曲线的测试显示，薄膜具有优良的磁和磁光性能。退火研究表明，随着退火时间的增加，矫顽力下降，垂直磁各向异性能减少，但克尔角变化不明显，其内在机制与薄膜中的微缺陷和应力的弛豫过程有关。     

退火对IrMn基自旋阀结构和磁性能的影响

采用高真空直流磁控溅射的方法制备了结构为//Ta(5nm)/Co75Fe25(5nm)/Cu(2.5nm)/Co75Fe25(5nm)/ Ir20Mn80(12nm)/Ta(8nm)的顶钉扎自旋阀多层膜,通过X射线衍射(XRD)、原子力显微镜(AFM) 和振动样品磁强计(VSM)研究了退火对自旋阀的结构及磁性能的影响.结果表明:退火使得IrMn(111)织构减弱,表面/界面粗糙度在低温退火后增大,而较高温度退火后减小;退火后交换偏置场和被钉扎层矫顽力减小,而自由层矫顽力增加;退火后自旋阀多层膜交换偏置场随样品在反向饱和场下停留时间的增加而不发生变化.     

溅射方法对FePt:Ag颗粒膜磁性能及微观结构的影响

分别采用共溅射和多层膜溅射方法制备了FePt:Ag颗粒膜.样品的磁性能和微观特性分别用振动样品磁强计(VSM)、磁力显微镜(MFM)和透射电镜(TEM)进行了表征.研究结果表明:多层膜溅射制备的FePt:Ag颗粒膜能在较低的退火温度下发生有序化相变;而共溅射制备的FePt:Ag颗粒膜经过相同的退火条件后,具有更高的矫顽力,及更细、分布更均匀的晶粒和磁畴结构.     

电沉积制备CuCo颗粒膜微观结构和巨磁电阻效应研究

采用电化学的方法在半导体Si表面沉积了CuCo颗粒膜.研究了膜层电沉积过程中颗粒膜生长的显微结构及热处理过程颗粒膜元素的分布情况.经过450℃退火处理1h后Cu80Co20薄膜GMR达到最大值,随着温度的升高膜层的电阻率也随之下降.面扫描元素分析和XRD分析表明经过退火处理膜层中出现Co粒子的析出,出现了局部富钴的区域.磁阻测量表明此时有利于提高膜层的GMR值.更高温度的退火处理使GMR值降低.磁性能测量发现随着退火温度的提高膜层的饱和磁化强度Ms、矫顽力Hc和剩余磁化强度Mr也随着变大.     

Pt浓度对磁控溅射制备Co1-xPtx:C薄膜的影响

采用组合靶,利用磁控共溅射技术制备了Co1-xPtx:C复合纳米颗粒薄膜,研究发现CoPt粒子取向和磁性能与CoPt:C薄膜中的Pt浓度有密切关系,在较高Pt浓度的CoPt：C薄膜中观察到垂直各向异性现象。通过改变Pt浓度,可以获得粒子粒径小于lOnm、矫顽力可控、高的垂直磁晶各向异性能的薄膜。综合考虑,薄膜的最佳成分为Co47Pt53:C,此时矫顽力达到最大。     

Annealing behaviour and magnetic properties of Co/Pt and Fe/Pt bilayer thin films

The annealing behaviour and magnetic properties of Co/Pt and Fe/Pt bilayer thin films are investigated. The coercivity of Co/Pt bilayer thin films increases with annealing above 450 °C and shows a peak value of 40 kA m⁻¹ in the range from 500 to 550 °C. This increase is due to both the formation of a CoPt solid solution and the optimization of grain diameters. Furthermore, the increase is promoted by multilayering. Similar results were obtained for Fe/Pt bilayer thin films.     

退火温度对SmCo永磁薄膜微结构及磁性能的影响

采用直流磁控溅射法制备SmCo薄膜,研究了退火温度对薄膜微结构及磁性能的影响。XRD分析结果表明,当退火温度为600℃时,SmCo5相析出,而Sm2Co17相在700℃析出。SEM照片可看出,退火温度高于900℃时,六方柱状的SmCo5相和菱方状的Sm2Co17相全部析出。随着退火温度的升高,晶粒尺寸增大,当温度达940℃时,晶粒尺寸减小,而在980℃时,晶粒尺寸又将增大。VSM测试表明,与制备态的薄膜相比,退火后的薄膜在垂直于膜面方向的矫顽力、剩余磁化强度及最大磁能积都增大。960℃时得到矫顽力和剩余磁化强度的最大值,800℃时得到最大磁能积的最大值。     

Large improvement of coercivity in Sm-(Co,Cu)/Fe films by Cu addition

The magnetic properties and microstructure of Sm-(Co,Cu)/Fe films were investigated systematically. The addition of Cu is helpful for keeping a better multilayer structure due to the reduction of the crystallization temperature of the hard phase. With lowering the temperature, the coercivity of the Sm-(Co,Cu)/Fe films increases rapidly with a linear relationship. The Cu addition significantly improves the coercivities of the Sm-(Co,Cu)/Fe multilayer films, especially at the low temperatures. Adding the Cu as well as lowering the temperature cause a large inhomogeneity in the hard phase, and therefore a high pinning coercivity.     

Structural, magnetic, and magneto-optical properties of nanocrystalline face centered cubic Co70Cr30/Pt multilayers with perpendicular magnetic anisotropy

Co70Cr30 alloyed layers are combined with extremely thin Pt layers in order to produce novel face-centered-cubic multilayered films to be considered as a potential perpendicular magnetic recording medium. The films were grown on Si, glass and polyimide substrates by e-beam evaporation at a temperature slightly higher than room temperature. The multilayered structure of the films was verified by X-ray diffraction experiments. Plane-view transmission electron microscopy images have revealed the formation of very small grains in the range of 7-9 nm. Hysteresis loops as a function of temperature were recorded via the magneto-optic Kerr effect in the polar geometry configuration. The system exhibits perpendicular magnetic anisotropy, which enhances with decreasing temperature. Hysteresis loops with a squareness of 1 and a coercivity of 1.45 kOe were obtained at 10 K. Furthermore, complete magneto-optic spectra of the films are recorded, showing a strong magneto-optic enhancement in the ultraviolet region at around 4.5 eV.     

High-density perpendicular magnetic recording media of granular-type (FePt/MgO)/soft underlayer

Perpendicular magnetic recording media, composed of granular-type FePt-MgO films on Fe-Ta-C soft magnetic underlayer (SUL), have been fabricated on to 2.5-in glass disks. [001] textured FePt granular films with high-perpendicular magnetic anisotropy were obtained by annealing the FePt/MgO multilayer films. The FePt grain size, perpendicular coercivity, magnetic activation volume, and the exchange coupling between the FePt grains were found to be strongly dependent on the initial multilayer structures and the annealing conditions. The recording performance of the disks was evaluated by a spin-stand. The obtained results reveal a close correlation between the recording performance and magnetic properties. The thermal stability of the granular-type FePt media was studied using high-temperature magnetic force microscopy (MFM) technique, equipped with in situ sample heating, in the temperature range 25/spl deg/C-200/spl deg/C. The estimated signal decay at high temperature is ascribed to the temperature dependent magnetic anisotropy behavior.     

Ultrafast heating effect on transient magnetic properties of L10-FePt thin films with perpendicular anisotropy

Laser-induced ultrafast magnetization dynamics and transient coercivity behavior in perpendicular magnetized L1₀-FePt films are investigated using the time-resolved polar magneto-optical Kerr technique. The magnetization after photo-excitation shows a dramatic reduction on the picosecond time scale. In contrast, the coercivity shows a weak decrease, accompanied by a skewed Kerr loop shape for low and intermediate fluences. The results can be interpreted by the laser-induced non-uniform demagnetization due to the weakened coupling between FePt grains of different size and/or components. The remaining coercivity vanishes when the film is fully demagnetized at higher fluence. We claim that the remaining coercivity can be manipulated by employing appropriate laser energy and film thickness, which may be helpful for application in heat-assisted magnetic recording.     

Sintering Effect of Annealed FePt Nanocrystal Films Observed by Magnetic Force Microscopy

Chemically synthesized FePt nanocrystals can exhibit room temperature ferromagnetism after being annealed at temperatures above 500degC. In thick films composed of FePt nanocrystals, the coercivity can be quite large. However, the coercivity of thin films has been found to decrease significantly with decreasing thickness, to the point that ferromagnetism at room temperature is lost. We studied 12 to 55 nm thick films by using magnetic force microscopy (MFM) under external applied fields. We made smooth films by spin casting 4-nm-diameter FePt nanocrystals and annealing them at 605degC-630degC. Thin FePt films showed lower coercivity than thick films. To help interpret the MFM images, we obtained complementary magnetic and structural data by superconducting quantum interference device (SQUID) magnetometry, transmission electron microscopy (TEM), and X-ray diffraction. We conclude that the magnetic properties of these films are strongly affected by nanocrystal aggregation that occurs during annealing