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.     

TbFe/Fe交换耦合磁致伸缩多层膜的制备

采用双靶磁控溅射法制备了 TbFe/Fe交换耦合磁致伸缩多层膜,考察了热处理时间、Fe层厚度、溅射功率以及Ar气分压对多层膜低场磁致伸缩性能的影响。研究结果表明:TbFe 磁致伸缩层与软磁 Fe层之间通过交换耦合作用以及热处理能明显提高薄膜的软磁性能和磁致伸缩性能;TbFe/Fe多层膜的磁致伸缩性能对热处理时间、Fe 层厚度、溅射功率、Ar 气分压等薄膜沉积参数十分敏感;与 TbFe 磁致伸缩薄膜相比TbFe/Fe交换耦合磁致伸缩多层膜水平方向的矫顽力从 16kA/m降低到 9.6 kA/m。在外加磁场为8000 A/m条件下,TbFe/Fe磁致伸缩多层膜最大磁致伸缩系数可达1.58×10-4。     

软硬磁层厚度对L1_0-FePt/Fe交换耦合双层膜磁性能的影响:模拟与实验

首先采用磁控溅射的方法在玻璃基片上沉积不同硬/软磁层厚度的FePt/Fe交换耦合双层膜,结合实验结果,依据微磁学理论对L10-FePt/Fe交换耦合双层膜的磁性能进行研究。结果显示,当FePt硬磁层厚度固定20nm,随Fe软磁层厚度的增加双层膜矫顽力逐渐减小。当Fe软磁层厚度超过其畴壁宽度时,其对矫顽力的影响大幅度降低。Fe软磁层厚度固定为10nm,FePt硬磁层厚度发生变化时,由于理论和实际双层膜界面的不同,导致对双层膜成核场起作用的临界硬磁层厚度也不一样。     

不同退火时间对[Ag/FePt]_(10)多层膜磁性能和微结构的影响

采用射频磁控溅射的方法,在玻璃基片上制备了不同Ag层厚度的[Ag/FePt 2nm]10多层薄膜,经550℃真空热处理后,得到L10有序结构的FePt薄膜.实验结果显示,FePt单层薄膜经550℃退火30min后其易磁化轴处于垂直方向和面内方向之间,而550℃退火60min后其易磁化轴处于垂直于膜面方向,垂直矫顽力和面内矫顽力分别为634和302kA/m;真空退火后[Ag/FePt]10多层膜表现为面内磁晶各向异性,550℃退火60min后[Ag 2.8nm/FePt 2nm]10多层薄膜垂直矫顽力和面内矫顽力分别为309和778kA/m,并且随着Ag层的加入,部分FePt颗粒已经被Ag原子隔开了,颗粒之间的交换耦合作用变弱了.     

Fe/V多层膜中亚稳结构Fe的形成及其磁学性能

采用电子束蒸镀的方法,通过改变多层膜的周期结构,成功地制备出具有不同晶格常数的bcc亚稳结构铁相的Fe/V多层膜,并研究了亚稳结构铁相形成对其磁性影响的规律.实验结果表明,多层膜中Fe与V层均由纳米晶粒组成.Fe层厚度小于2nm时,受多层膜界面自由能作用,Fe与V相互准外延生长,多层膜由点阵常数一致的体心立方相组成,其点阵常数随样品V/Fe层厚度比的增大而增加.多层膜平均原子磁矩随铁或钒层厚度的改变发生明显变化:当钒层厚度固定为6nm时,铁原子磁矩随铁层厚度的增加逐渐下降,在2nm处出现极小值后又随铁层增厚而回升;对于铁层厚度固定为1.6nm的样品,磁矩在钒层厚度为3nm时出现极大值.     

FePt单层连续膜和颗粒膜的制备与磁性能研究

利用磁控溅射在不同Ar气压下制备了不同膜厚的FePt薄膜。利用透射电镜(TEM)研究了溅射气压和膜厚对薄膜形貌的影响,利用振动样品磁强计(VSM)研究了溅射气压和膜厚对薄膜磁性能的影响。结果表明溅射气压和膜厚对溅射态单层FePt薄膜的表面形貌、颗粒尺寸有很大影响。随着溅射气压的增大,颗粒尺寸减小,从连续膜转变成颗粒膜;随着膜厚的增加,颗粒尺寸变大,从颗粒膜变成连续膜。通过调节溅射气压可以控制FePt的岛状结构,从而获得较理想的FePt颗粒薄膜。溅射气压和膜厚对经过热处理的L10-FePt薄膜的磁性能有很大影响。随着溅射气压增加,形核场由正值转变成负值,矩形比有增大趋势;随着厚度的增加,无序-有序相转变更充分。     

Fe/Mo,Co/Mo多层膜的结构与磁性研究

利用离子束溅射方法制备了具有不同调制周期的Fe/Mo和Co/Mo金属磁性多层膜,并比较系统地研究了它们的结构和磁性。通过结构研究发现,Fe/Mo和Co/Mo系统的多层膜都具有良好的周期调制结构;当多层膜的调制周期比较大时,多层膜样品表现出一定的择优取向关系,而多层膜调制周期比较小时,多层膜内部的结晶状态变差甚至变为微晶(Fe/Mo系统)或非晶态(Co/Mo系统)。结合磁性测量的结果发现,对于Co/Mo系统多层膜样品,在Co-Mo界面处存在有金属中间化合物构成的“死层”,它的存在使得多层膜的饱和磁化强度随着Co的单层厚度的减小而下降。     

添加AlN对FePt薄膜结构和磁性的影响

采用射频磁控溅射制备了FePt(50nm)和[FePt(2,3,5nm)/AlN(1nm)]n膜,之后在550℃退火30min,研究了周期数(n)和AlN含量对[FePt/AlN]_n系列多层膜结构及磁性的影响.结果表明,多层膜的矫顽力和矩形比均在n=8时出现较大值;周期数的增大会引起晶粒尺寸的长大;AlN的加入不但可以抑制FePt粒子的长大,使晶粒体积(V_grain)和磁激活体积(V*)趋于一致,而且还能有效地降低晶粒间交换耦合作用,并且AlN含量越大,晶粒间交换耦合作用的程度越弱.     

磁场退火制备FePt/Ag垂直磁化薄膜

采用磁控溅射法在自然氧化的单晶Si（100）基底上制备了（FePL／Ag）10多层薄膜,并在10kA／m磁场中进行了不同温度的真空热处理,研究了磁场作用下,不同热处理温度对FePt薄膜有序化转变及磁性能的影响。X射线衍射研究表明,在磁场作用下通过多层膜设计可以比较容易获得垂直生长的易磁化轴;选择适当的热处理温度、降低多层膜中每层膜厚可以制备出晶粒尺寸细小均匀的FePL／Ag垂直磁化薄膜,适用于高密度垂直磁记录介质材料。     

磁控溅射Fe-N薄膜及Fe-N/TiN多层膜的结构和磁性

用磁控溅射法制备了Fe N薄膜和Fe N/TiN多层膜。结果表明 ,在常温下 ,使用较小的氮、氩比溅射 ,生成的Fe N薄膜主要是含氮α Fe固溶体 ,并且N原子进入α Fe晶格是饱和磁化强度提高的一个原因。Fe N/TiN多层膜的层间耦合作用以及减小每一Fe N层厚度而引起的晶粒尺寸的减小可以有效地降低薄膜的矫顽力 ,从而获得更好的软磁性能     

Effects of Os inserted layers on the microstructures and magnetic properties of the FePt films

The microstructure and magnetic properties of multilayer [Os(t)/FePt(x)]n films on a glass substrate with a 10 nm Os buffer layer by ion beam sputtering have been studied as a function of the annealing temperatures between 300 and 800 degrees C. Here, t = 0.2, 1 or 5 nm and x varied from 10, 20, 25, 50, to 100 nm with its associated n value of 10, 5, 4, 2, and 1, respectively. No diffusion evidence was found in samples with a thin Os layer and t > or = 1 nm. The average grain size of the multilayer films can be well controlled by both annealing temperature and thickness of the FePt layer by a very thin Os space layer with t > or = 1 nm. The enhancement of H(c) can be understood from the fact that for a FePt film with an Os spacer layers, the increasing number of Os layer will inhibit the grain growth of FePt grains and enriches the grain boundary. We have experimentally demonstrated that even with a very thin 1 nm Os spacer layers, the [Os(t)/FePt(x)]n multilayer films can exhibit good hard magnetic properties and are attractive candidates for ultrahigh density magnetic recording media.     

Structure and magnetic property of the FePt/CrPt bilayer

In this work we have studied the growth sequence of L10-CrPt antiferromagnetic layer effects on the microstructure and magnetic properties of the FePt/CrPt bilayer. The microstructure characteristics were investigated by means of X-ray diffraction and the magnetic properties were measured at room temperature by using a vibrating sample magnetometer. Structural analysis showed that the low-temperature ordering and the in-plane orientation of the FePt layer with the CrPt underlayer were promoted due to lattice mismatch optimized after annealing at 350 degrees. Meanwhile, magnetic analysis also revealed that the FePt/CrPt bilayer had much larger exchange bias (H(E)) and higher coercivity (Hc) when the CrPt layer was as the underlayer after annealing at 350 degrees.     

Low temperature ordering of FePt films by in-situ heating deposition plus post deposition annealing

FePt thin films with 40 nm thickness were prepared on thermally oxidized Si (001) substrates by dc magnetron sputtering at the nominal growth temperature 375 °C. The effects of annealing on microstructure and magnetic properties of FePt thin films were investigated. The as-deposited FePt thin films show soft magnetic properties. After the as-deposited FePt thin films were annealed at various temperatures and furnace cooled, it is found that the ordering temperature of L1₀ FePt phase could be reduced to 350 °C. For FePt thin films annealed at 350 °C, the in-plane and out-of-plane coercivities of the films increased to 510 and 543 kA/m, respectively, and the films had hard magnetic properties. A highly (001) orientation was obtained, when FePt thin films were annealed at 600 °C. And the hysteresis loops of FePt thin films annealed at 600 °C show out-of-plane magnetic anisotropy.     

Coercivity variation in exchange-coupled Fe/FePt bilayer with perpendicular magnetization

The soft/hard Fe/FePt film with perpendicular magnetization has been deposited on a glass substrate. The (001) oriented L1₀ FePt film was obtained when annealed by rapid thermal process at 800 °C and a Fe layer was deposited at room temperature with thicknesses of 2 nm to 20 nm. Controlling the Fe layer thickness allowed modification of the hysteresis loops from out-of-plane rigid magnet to in-plane exchange-spring like magnet due to the nanometer scale interface coupling. When the Fe layer thickness increased to 2 nm, the out-of-plane coercivity is reduced to 5.9 kOe but the remanence ratio (0.98) is still high. The Fe (2 nm)/FePt film shows perpendicular magnetization with linear in-plane hysteresis loop. The remanence ratio is reduced to 0.85 when the Fe layer thickness increased to 5 nm. When the Fe layer thickness was varied up to 10-20 nm, the in-plane hysteresis loop shows exchange-spring like behavior with two-step magnetization reversal processes. The films with perpendicular coercivity were moderated by the thickness of soft magnetic layer.     

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     

Self-assembled nano-size FePt islands for ultra-high density magnetic recording media

To find a method to form nano-size FePt alloy for ultra-high density magnetic recording media, this work concentrated on the formation mechanisms of nano-island FePt films on amorphous glass substrates. FePt films of different thicknesses (1-10 nm) were deposited on amorphous glass substrates and post-annealed at 700 °C for 10 and 30 min. The configuration of the film changed during the annealing process due to the surface energy difference between the glass substrate and FePt alloy. Investigation of the microstructures and magnetic properties of the ordered L1₀ FePt films revealed that the 1 nm FePt film annealed at 700 °C for 10 min had perpendicular magnetic anisotropy and good reproducibility of forming well-separated FePt nano-size islands for ultra-high density magnetic recording media.     

Effects of Magnetic Annealing on Structure and Magnetic Properties of L10-FePt/Ag Films

The structural and magnetic properties of L1₀-FePt/Ag films were studied by X-ray diffraction and a vibrating sample magnetometer. The FeAg/Pt films were obtained by depositing FeAg thin films on thermally oxidized Si (001) substrates via magnetron sputtering and Pt layers on their surface after annealing FeAg thin films at 400 °C with and without an out-of-plane magnetic field of 10 kOe. These films were further annealed at various temperatures to obtain L1₀-FePt phase. The results indicated that the pre-annealing of FeAg thin films under 10 kOe magnetic field caused (001) orientation of Fe particles, and the deposition of Pt layer on such orientated underlayers reduced the ordering temperature of FePt in FeAg/Pt films, realizing the L1₀-FePt phase at 400 °C. The higher coercivity and ordering degree were also observed in the samples, compared with those pre-annealed without magnetic field at the same annealing condition.     

Effect of carbon additive on microstructure evolution and magnetic properties of epitaxial FePt (001) thin films

FePt:C thin films were deposited on CrRu underlayers by DC magnetron co-sputtering. The effects of C content, FePt:C film thickness and substrate temperature on the microstructural and magnetic properties of the epitaxial FePt (001) films were studied. Experimental results showed that even with 30 vol.% C doping, the FePt films could keep a (001) preferred orientation at 350 °C. When a FePt:C film was very thin (< 5 nm), the film had a continuous microstructure instead of a granual structure with C diffused onto the film surface. With further increased film thickness, the film started to nucleate and formed a column microstructure over continuous FePt films. A strong exchange coupling in the FePt:C films was believed to be due to the presence of a thin continuous FePt layer attributed to the carbon diffusion during the initial stage of the FePt:C film growth. Despite the presence of a strong exchange coupling in the FePt:C (20 vol.% C) film, the SNR ratio of the FePt:C media was about 10 dB better than that of the pure FePt media. The epitaxial growth of the FePt:C films on the Pt layers was observed from high resolution TEM cross sectional images even for the films grown at about 200 °C. The TEM images did not show an obvious change in the morphology of the FePt:C films deposited at different temperatures (from 200 °C to 350 °C), though the ordering degree and coercivity of the films increased with increased substrate temperature.     

The effect of composition and structural ordering on the magnetism of FePt nanoparticles

Spherical 4 nm FePt nanoparticles were synthesized by the simultaneous decomposition of Fe(CO)5 and the polyol reduction of Pt(acac)2. The final Fe-to-Pt composition was tuned between 15-55 at.% by varying the ingredient precursor ratios. The effect of composition and structural ordering on the macroscopic magnetic features of final FePt nanoparticles was examined via post-synthetic annealing stages at different conditions. Structural ordering is promoted in all cases, though samples approximating equiatomic Fe/Pt ratios eventually transform to fct-FePt phase while the FePt3-phase is favored for the Pt-richer samples. Consequently, the magnetic features of the annealed nanoparticles may be categorized; the hard magnetic FePt region dominating for Fe content between 40-55 at.% and the soft magnetic FePt3 region dominating in the region 20-30 at.% while Fe content less than 20 at.% results in Pt-richer phases with diminishing ferromagnetic behavior.     

Nano-structure formation of Fe-Pt perpendicular magnetic recording media co-deposited with MgO, Al2O3 and SiO2 additives

Perpendicular magnetic recording media samples were prepared by sputter deposition on sapphire with a layer sequence of MgO seed-layer/Cr under-layer/FeSi soft magnetic under-layer/MgO intermediate layer/FePt-oxide recording layer. The effects of MgO, Al₂O₃ and SiO₂ additives on the morphology and orientation of the FePt layer were investigated by transmission electron microscopy. The samples exhibited (001) orientation of the L1₀ FePt phase with the mutual orientations of sapphire substrate//MgO(100)[001]//Cr(100)[11¯0]//FeSi(100)[11¯0]//MgO(100)[001]//FePt(001)[100]. The morphology of the FePt films varied due to the co-deposited oxides: The FePt layers were continuous and segmented by stacking faults aligned at 54° to the surface. Films with SiO₂ addition, beside the oriented columnar FePt grains, exhibited a fraction of misoriented crystallites due to random repeated nucleation. Al₂O₃ addition resulted in a layered structure, i.e. an initial continuous epitaxial FePt layer covered by a secondary layer of FePt-Al₂O₃ composite. Both components (FePt and MgO) of the MgO-added samples were grown epitaxially on the MgO intermediate layer, so that a nano-composite of intercalated (001) FePt and (001) MgO was formed.The revealed microstructures and formation mechanisms may facilitate the improvement of the structural and magnetic properties of the FePt-oxide composite perpendicular magnetic recording media.