制备条件对金属纳米线阵列磁性的影响

用电化学沉积方法在多孔Al2O3模板的孔道中制备了平均直径约为200 nm,长为60μm的磁性金属纳米线有序阵列. 电沉积电流密度较小时,制得的样品有较大的剩磁比和较强的矫顽力,并分别在 θ=90°和 30°达到极大值. 随着电流密度的增加,剩磁比和矫顽力降低. 在电沉积过程中外加磁场对磁晶的取向产生重大影响,导致磁性金属纳米线有序阵列的矫顽力和剩磁比发生相应的变化.     

淀积磁场对NiO／Ni81Fe19双层膜特性的影响

用射频磁控溅射法在外磁场中淀积 Ｎｉ Ｏ／ Ｎｉ８１ Ｆｅ１９ 双层膜, 利用淀积磁场（ Ｈｄｅ） 诱导易轴并确定交换耦合场方向． 研究了淀积磁场对 Ｎｉ Ｏ／ Ｎｉ Ｆｅ 双层膜特性的影响, 结果表明, 淀积磁场改善了双层膜的磁滞回线的矩形度, 减小矫顽力, 增强交换耦合作用． 反铁磁性层 Ｎｉ Ｏ 和铁磁性层 Ｎｉ Ｆｅ 的厚度对矫顽力和交换耦合作用有很大的影响． 在５６ｋ Ａ／ｍ 的磁场中制备的 Ｎｉ Ｏ （５０ｎｍ） ／ Ｎｉ Ｆｅ （２５ｎｍ） 双层膜的易轴矫顽力 Ｈ Ｃ为１ ． ９ｋ Ａ／ｍ , 交换耦合场 Ｈ Ｅ Ｘ为２ ． ６ｋ Ａ／ｍ , 临界温度 Ｔｃ 为１５０ ℃, 截止温度 Ｔ Ｂ为２３０ ℃     

高能球磨FeCo+MnO的结构与磁性研究

用高能球磨采用两种方案制备了FeCo MnO体系,并用X射线衍射和振动样品磁强计对其结构和磁性质做了分析.发现采用直接氧化Mn而得到MnO的方法,所得体系的MnO较纯;而通过分解MnCO3得到MnO的体系,MnO纯度较低,有较多Mn3O4杂质,两种方法制备的FeCo MnO体系的矫顽力和剩磁比都比单纯FeCo体系的增加很多,且前一种方法比后一种方法制备的FeCo MnO体系的矫顽力和剩磁比较大.然后研究了球磨时间及退火处理对FeCo MnO体系矫顽力及剩磁比的影响,发现球磨时间为120h体系的矫顽力和剩磁比最大;经过退火处理后,体系的矫顽力和剩磁比都有较大幅度的增加.     

永磁材料磁性检验中应注意的问题

表征永磁材料磁特性的特征参量是剩磁,矫顽力和最大磁能积,特征量的测定是通过测量退磁曲线而获得,测量退磁曲线最基本的方法是感应法。本文主要讨论如何用感应法准确测量退磁曲线,从而确定材料的特征参量。一、饱和磁化场的选取由于永磁有高的矫顽力,要饱和磁化,一般要求磁化场达到材料内禀矫顽力的三到五倍,并要求它的保持时间足以克服由于涡流引起的滞后。我国标准规定:当磁场增加50％时,试样磁化强度的变化不大于1％,则认为试样已达到饱和磁化。表1给出了常见各类永磁材     

Nd_2Fe_(14)B/α-Fe交换耦合双层薄膜磁性能

利用微磁学理论模拟计算了Nd2Fe14B/α-Fe交换耦合双层膜的磁滞回线,并对双层膜体系的剩磁、矫顽力、最大磁能积与软磁层厚度的关系进行了研究。结果显示,软磁层厚度小于临近尺寸时,磁滞回线为矩形,双层膜完全耦合;软磁层厚度与磁性能的关系表明,随着软磁层厚度的增加,剩磁和最大磁能积先增大后减小,而矫顽力单调下降。     

日本复合半硬磁材料的新近发展

一、引言半硬磁材料,就其矫顽力值来看,属于硬磁材料范围;但在使用过程中,它又像软磁材料那样,在外加磁场作用下进行磁化反转。半硬磁材料的应用大致可以分为两大类,即利用材料磁滞特性的磁滞电机类和利用材料高剩余磁感应、高矩形比的继电器类。其中后者使用半硬磁材料做铁心只有20年的历史。     

阳极氧化铝底层对SmTbCo薄膜磁性能与结构影响的研究

采用两次阳极氧化法制备了孔洞排列有序的多孔氧化铝基底,并在其上用磁控溅射法制备了SmTbCo垂直磁化膜. 振动样品磁强计（VSM）测试结果显示,加入阳极氧化铝底层后可以将SmTbCo薄膜的矫顽力从370kA/m提高到530kA/m,并且随着氧化铝底层孔洞直径的减小,上层SmTbCo磁性薄膜的矫顽力与剩磁矩形比随之增大. 由薄膜断面的扫描电镜（SEM）照片可以看出,阳极氧化铝底层由于其自组织效应所形成规则密集的六角边形多孔结构能够明显促使上层的SmTbCo磁性薄膜生成柱状结构. 这一柱状结构提高了薄膜的矫顽力,从而拓宽了SmTbCo薄膜材料在超高密度垂直磁记录中的应用.     

低铁磁共振线宽BaFe12O19六角铁氧体的制备及其性能

本研究通过磁场成型技术制备高取向度、高剩磁比的BaFe12O19六角铁氧体;研究助烧剂对BaFe12O19六角铁氧体剩磁比、矫顽力、气孔率及铁磁共振线宽的影响;通过铁磁共振线宽测试,分析各向异性致宽、气孔致宽对铁磁共振线宽的贡献.测试结果表明,样品的最优剩磁比为0.87,铁磁共振线宽为220 Oe.分析结果表明,铁磁共振线宽主要来源于气孔致宽,且磁场成型技术和助烧剂都有利于降低材料的铁磁共振线宽.     

Sm(Co_(0.74)Cu_(0.12)Fe_(0.1)Zr_(0.04))_(7.5)纳米晶烧结磁体的结构和磁性能

采用放电等离子烧结技术制备了致密纳米晶SmCoCuFeZr烧结磁体,研究了磁体的结构和磁性能.X衍射结果表明,烧结磁体具有TbCu_7结构.TEM观察显示,烧结磁体平均晶粒尺寸为35nm.室温时磁体的剩磁为0.49T,矫顽力高达1.42T,而剩磁比Mr/Ms为0.63,表明在纳米晶之间存在晶间交换耦合作用.     

玻璃包覆Fe79-xCox Si8 B13非晶合金微丝的磁性能

实验以熔融纺丝法制备的玻璃包覆Fe79-xCoxSi8B13非晶合金微丝为对象,分析了微丝成分、尺寸以及玻璃包覆层去除对微丝静磁性能的影响。研究结果表明,玻璃包覆Fe79-xCoxSi8B13非晶合金微丝存在明显的磁各向异性,微丝轴向为易磁化方向;随着Co含量的增加,微丝的饱和磁化强度先增大后减小,Co含量为10%的Fe69Co10Si8B13非晶合金微丝饱和磁化强度最高,为1323emu·cm-3;对于玻璃包覆Fe69Co10Si8B13非晶合金微丝,当芯丝半径与玻璃包覆层厚度比值k约小于0.5时,其轴向磁滞回线为近矩形,表现出大巴克豪森效应;微丝的轴向剩磁比随k值的增大而减小,而微丝径向剩磁比保持很小,仅0.03左右;微丝的轴向和径向矫顽力均随比值k的增大而减小;当芯丝半径为10.9μm、玻璃包覆层厚度为9.7μm(k为1.12)时,去除包覆层后微丝的轴向矫顽力降低30%、径向矫顽力降低11%;而轴向剩磁比降低33%、径向剩磁比降低67%。     

Magnetic properties of cobalt rare-earth thin films

This paper describes the magnetic properties of dc sputtered thin films of Co-Gd and Co-Sm in various compositions. Magnetic moment density, hysteresis loop coercivity and squareness, and rotational hysteresis loss measurements are reported. Crystallite and domain sizes were observed with an electron microscope for a few compositions. A tentative model of magnetization reversal is proposed for some of the compositions.     

Structure and Magnetic Properties of BaCoTiFe10O19 Thin Films with an Easy-Axis In-Plane Orientation

BaCoTiFe10O19 hexaferrite thin films with an easy-axis in-plane orientation were prepared by crystallization of amorphous films deposited by rf magnetron sputtering. The structure and magnetic properties were investigated. It is shown that CoTi-doping leads to a reduction of spontaneous magnetization and magnetic moment, which is caused by non-collinear magnetic structure and surface spin canting of small particles. The substitution of CoTi for Fe can adjust coercivity and Curie temperature over a very wide range, while still maintaining the room temperature magnetization. It is found that BaCoTiFe10O19 films exhibit a large squareness of hysteresis loop, Sq = 0.68. Thus, this film is desirable for high-density longitudinal recording systems.     

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.     

Magnetic behavior of cobalt oxide films prepared by pulsed liquid injection chemical vapor deposition from a metal-organic precursor

Thin films of cobalt oxide were prepared by the pulsed liquid injection chemical vapor deposition technique from metal-organic precursor. By using a β-diketonate complex of cobalt, namely cobalt (II) acetylacetonate (Co(acac)₂) as the precursor, oxygen as the reactant and argon as the carrier gas, cobalt oxide films 100 nm in thick were deposited onto Si (100) substrates at 650 °C in about 40 min. According to the characterization by X-ray diffraction and atomic force microscopy, smooth and polycrystalline films, consisting exclusively of the Co₃O₄ phase, were deposited. Magnetic properties, such as saturation magnetization, the remanence, the coercivity, the squareness ratio and the switching field distribution, were extracted from the hysteresis loop. Cobalt oxide films with coercivities of 6.61 mT, squareness ratio of 0.2607 and saturation magnetization of 12.17 nA m², corresponding to a soft magnetic material, were achieved.     

Interaction Effects in SmCo/FeCo Bilayer Film Media

The magnetic property of Sm22Co78/Fe65Co35 bilayer film media prepared by magnetron sputtering was measured. All the samples have in-plane anisotropy and the hysteresis loops are simple single loops, indicating that the two phases are strongly exchange-coupled. The reduced remanence (Mr/Ms) was found to increase from 0.58 to 0.8 with increasing Fe65Co35 layer thickness (d) for a fixed Sm22Co78 layer thickness. The coercivity was found to increase with increasing a few Fe65Co35 layer, and then to decrease with continuously increasing Fe65Cos5 layer. The intergranular exchange and magnetostatic interaction effects were measured from their remanence magnetization curves.     

Angular variation of coercivity in thin-film media by micromagneticmodel

A computer micromagnetic simulation model is employed to study the angular variation of coercivity (out of plane) in thin-film media. Each grain of the film is uniformly magnetized and switches coherently according to the S-W model. The M-H hysteresis loops for applied fields at different angles to the film plane are obtained for various magnetostatic interaction parameters, quantum exchange constants, and easy axis distributions. The angular variation of the coercivity curve exhibits a peak if there is magnetostatic interaction among the grains and qualitatively follows the experimental results well. The peak in the angular variation of coercivity is seen to result from the demagnetizing field. The rotational hysteresis process is also investigated by means of this model     

Nanoscale control of exchange bias with BiFeO3 thin films

We demonstrate a direct correlation between the domain structure of multiferroic BiFeO3 thin films and exchange bias of Co 0.9Fe 0.1/BiFeO3 heterostructures. Two distinct types of interactions - an enhancement of the coercive field ( exchange enhancement) and an enhancement of the coercive field combined with large shifts of the hysteresis loop ( exchange bias) - have been observed in these heterostructures, which depend directly on the type and crystallography of the nanoscale ( approximately 2 nm) domain walls in the BiFeO3 film. We show that the magnitude of the exchange bias interaction scales with the length of 109 degrees ferroelectric domain walls in the BiFeO 3 thin films which have been probed via piezoresponse force microscopy and X-ray magnetic circular dichroism.     

Magnetization reversal in sputtered Co-Cr films

The magnetic characteristics of a set of r.f. sputtered Co-Cr films of various composition and thickness are examined in order to evaluate their performance for perpendicular recording. The mechanism of the magnetization reversal is discussed on the bases of: i) the shape of the rotational hysteresis loss as a function of the internal rotating field, ii) the value of the rotational hysteresis integral, iii) the dependence of the coercivity Hc, and the remanence coercivity Hr, on the angle between the easy direction and the field direction. In particular the measurements of rotational hysteresis were performed by monitoring the rate of change of the angular velocity of a top containing the specimen spinning in a magnetic field perpendicular to its axis. The deviation of the experimental behaviour from the ideal models are related to the amount of anomalies in the columnar structure of the film.     

Remanence and coercivity in exchange-coupled amorphous Nd50Fe50/Fe multilayers

The hysteresis behavior of sputteredNd₅₀Fe₅₀/Fe multilayers consisting of alternate layers of magnetically hard Nd₅₀Fe₅₀ and sof α-Fe phases with a bilayer thickness in the range of 20–40 nm has been investigated. Samples prepared at 5 nTorr Ar gas pressure showed a uniform single-phase hysteresis loop, with increased reduced remanence (0.6) for Fe layer thickness under 7.5 nm, which is attributed to a strong exchange coupling between the hard Nd₅₀Fe₅₀ and soft α-Fe. Samples sputtered at higher gas pressures showed smooth loops for larger critical Fe thickness, with a higher coercivity and a lower reduced remanence.