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。     

SmCo/FeCo/SmCo三层膜中的剩磁增强效应

系统地研究了磁控溅射制备的Sm22Co78/Fe65Co35/Sm22Co78三层膜系统中，当软磁相的体积分数一定时，矫顽力和剩磁比随FeCo软磁层厚度（d)的变化，所有样品的磁滞回线均为单一硬磁相特征：说明FeCo软磁层与SmCo硬磁层之间的交换相互作用，使两相很好地复合在一起。当软磁相的体积分数为15％，20％，30％的情况下，矫顽力随d的变化都出现峰值，而剩磁比则单调增加，当体积分数为50％时，矫顽力随d的增加滑有峰值，但剩磁比还是单调增加，随着软磁体积分数的增加，矫顽力峰值及峰值位置都是单调减少。     

不同结构Sm-Co/α-Fe薄膜体系磁性能的研究

根据微磁学模拟理论,设置交换耦合双层膜中的Sm-Co硬磁层和α-Fe软磁层薄膜总厚度各自保持不变,通过改变结构来研究其对磁化反转过程和磁性能的影响。结果表明,从双层膜变化到三层膜的过程中,不同的结构具有不同的磁性能和磁化反转过程;当结构优化为Sm-Co(10 nm)/α-Fe(5 nm)/Sm-Co(10 nm)三层膜时,最大磁能积和矫顽力达到最大值,分别为1.4×10~6A/m和856.05 k J·m~(-3)。此结论对高性能交换耦合类磁性薄膜的制备具有一定的指导意义。     

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 ℃     

SmCo/Fe系统膜厚对矫顽力与过渡区噪声影响的微磁学模拟

SmCo/Fe双层膜具有很好的各向异性,因此能够用于高密度垂直磁记录中.采用微磁学方法,详细讨论了SmCo/Fe双层膜系统中膜层厚度对于矫顽力和记录位间的过渡区噪声的影响.模拟结果表明,硬磁层和软磁层厚度对于矫顽力和过渡区噪声都具有一定的影响.为了获得大的系统矫顽力和小的过渡区噪声,有必要提高SmCo层和Fe层的厚度比,同时也要将系统中膜层厚度控制在较小的值.     

SmCo_5/Co纳米复合多层膜的成核场

由于交换耦合纳米复合多层膜体系同时拥有硬磁相的高矫顽力和软磁相的高剩磁的优点,因此引起了业界的广泛关注。该文运用微磁学方法,并采用计算机进行模拟,系统地研究了交换耦合SmCo_5/Co多层膜体系退磁中的磁化反转过程,得到了纳米复合多层膜体系的成核场。研究发现交换耦合SmCo_5/Co多层膜体系成核场H_N随硬磁相厚度L~h和软磁相厚度L~s变化而变化的规律,成核场随软磁相厚度的增大而减小,随硬磁相厚度的增大而增大;当软、硬磁相厚度同时增大时,成核场受到的影响会变小;当硬磁相厚度L~h5nm时,软磁相对成核场起主导作用而硬磁相对成核场的影响可以忽略不计。     

NiO/CoFe双层膜的交换机制研究

通过改变制备NiO薄膜的氩气压和衬底材料,研究了NiO的结构、表面粗糙度对NiO/CoFe双层膜交换耦合场Hex的影响.实验表明完全自旋未补偿面与交换耦合场的产生没有直接联系,但交换耦合场Hex与界面状况密切相关.增大NiO的表面粗糙度会使交换耦合场Hex减小.应用随机场理论在考虑了实际界面存在的粗造度、杂质和缺陷等实际情况下,正确地预测了交换耦合场的数量级,而且对交换耦合场与铁磁层厚度tFM、反铁磁层厚度tAFM以及交换耦合场的温度特性等实验结果做出了合理解释.并应用随机场模型对反铁磁/铁磁双层膜中铁磁层矫顽力Hc与铁磁层厚度tFM的关系进行了定量计算,发现矫顽力Hc与铁磁层厚度1/tFM成正比,这一结果表明理论计算与我们的实验数据符合得很好.     

柔性衬底上Ni_(81)Fe_(19)/Ni_(50)Mn_(50)双层膜交换偏置效应研究

目的:探究制备在聚酰亚胺PI柔性衬底上的Ni_(81)Fe_(19/)Ni_(50)Mn_(50)双层膜的交换偏置效应。方法:采用直流磁控溅射技术分别在硅片和PI衬底上制备Ni_(81)Fe_(19)/Ni_(50)Mn_(50)双层膜,经相同温度退火处理后使用振动样品磁强计测试样品的磁滞回线。结果:柔性衬底上生长的双层膜的交换偏置场大小基本等于硅衬底上生长的,但其矫顽力始终比硅衬底上的大;薄膜的交换偏置场和矫顽力随着铁磁层厚度增大呈线性减小,随着反铁磁层厚度增大呈先增大后减小最后稳定的趋势,柔性衬底上薄膜的交换偏置场和矫顽力还会随着测量温度的升高而下降直至消失。结论:Ni_(81)Fe_(19/)Ni_(50)Mn_(50)双层膜的交换偏置场和矫顽力会受到铁磁层厚度、反铁磁层厚度和测量温度的影响,其中矫顽力还会受到衬底类型的影响。     

基于矫顽力与剩磁的铁磁性材料应力测量

铁磁性材料的磁滞回线代表其在外加磁场下的基本磁特性,磁滞回线反映的磁特性参数磁导率μ、矫顽力H_C、剩磁M_R能灵敏地反应铁磁性材料的微观组织结构。针对铁磁性材料受应力易发生形变的问题,该文研究铁磁性材料内部磁畴结构和所受应力的关系,利用应力引起的磁特性参数的变化确定材料所受的应力大小,基于U型磁轭的电磁检测原理,测量激励线圈中的电流值和感应线圈上的电压值,采集被测磁回路的磁滞回线并计算矫顽力、剩磁。结果表明:矫顽力数值会随拉力的增大而升高,剩磁随拉力的增大呈阶段性变化,利用矫顽力与剩磁可以实现铁磁性材料的受力分析。     

回收制备烧结Nd-Fe-B磁体的磁性能与耐热性能

以废旧钕铁硼磁体为原料,采用短流程回收制备技术制备了烧结Nd-Fe-B磁体,通过添加镨钕混合稀土研究了磁体的磁性能和耐热性能。结果表明,在回收磁体中添加2%PrNd,制备的烧结Nd-Fe-B磁体的剩磁为1.31T、矫顽力为1 474.86kA/m、磁能积为353.90kJ/m~3。与一次成品相比矫顽力恢复到102%,剩磁恢复到95%,磁能积恢复到90%。在293~393K范围内未掺杂PrNd磁体的矫顽力温度系数为-0.589 9%/K,掺杂2%PrNd磁体的矫顽力温度系数为-0.556 4%/K,提高了磁体在高温下的耐热性能。这是由于添加混合稀土PrNd增强了主相晶粒间的去磁交换耦合作用,提高了主相的磁晶各向异性场,从而提高了磁体的矫顽力和耐热性能。     

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.     

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.     

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.     

Magnetic hysteresis properties of internally oxidised Ni-Si alloys

Results are presented of magnetic hysteresis measurement made on some internally oxidised Ni-Si alloys. The alloys investigated were originally of nominal composition 0.058, 0.48, 0.77 and 0.96 wt % Si in Ni. Hysteresis loops have been obtained for all the alloys in both unoxidised and several internally oxidised states using a standard technique. The effect of the internal oxide precipitation on the coercivity and remanence of the specimens is made clear by these measurements. The dependence of coercivity on precipitate morphology and alloy compositions is considered and results of the variation of coercivity with the temperature of measurement in the range 20 to 265° C are discussed.     

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.     

Engineering magnetic nanostructures with inverse hysteresis loops

Top-down lithography techniques allow the fabrication of nanostructured elements with novel spin configurations,which provide a new route to engineer and manipulate the magnetic response of sensors and electronic devices and understand the role of fundamental interactions in materials science.In this study, shallow nanostructure-pattemed thin films were designed to present inverse magnetization curves,i.e.,an anomalous magnetic mechanism characterized by a negative coercivity and negative remanence.This procedure involved a method for manipulating the spin configuration that yielded a negative coercivity after the patterning of a single material layer.Patterned NiFe thin films with trench depths between 15％-25％ of the total film thickness exhibited inverse hysteresis loops for a wide angular range of the applied field and the trench axis.A model based on two exchange-coupled subsystems accounts for the experimental results and thus predicts the conditions for the appearance of this magnetic behavior.The findings of the study not only advance our understanding of patterning effects and confined magnetic systems but also enable the local design and control of the magnetic response of thin materials with potential use in sensor engineering.     

A Low-Field Scaling Rule of Minor Hysteresis Loops in Plastically Deformed Steels

A scaling rule of magnetic minor hysteresis loops at low applied fields has been examined in plastically deformed low carbon steel and pure Ni. It was found that a power law between hysteresis loss and remanence of a minor loop holds true over the wide range of magnetization from the very low to intermediate range unlike the well-known Steinmetz law. The power-law exponent was an almost constant value of 1.35 being independent of the types of magnetic materials, the level of plastic deformation, and sample shape. The coefficient of the scaling rule increases with deformation and is in linear proportion to coercivity. This behavior was qualitatively explained on the basis of the Rayleigh law and NÉel theory.      

Two-axis magnetisation analysis of epitaxial cobalt films

Cobalt films were grown by molecular beam epitaxy on CaF2 buffer layers on silicon. Due to unique properties of CaF2/Si(100) interface, the surface of CaF2 has grooves along [110] direction. Cobalt grown on it has in-plane uniaxial magnetic anisotropy with easy axis along the grooves. The dependence of remanence magnetisation and coercivity on azimuth angle (between the grooves and field) follows single domain model in the range from 0 to 80 degrees. For hysteresis loops of both parallel and perpendicular components of magnetisation, quantitative agreement was achieved within the model of coherent rotation with certain distribution of anisotropy energy over regions of the sample. Between 80 degrees and 90 degrees, the film splits into multiple domains.     

工业纯铁退火过程中的位错密度和磁性能EI北大核心CSCD

针对热轧工业纯铁退火过程的微观组织和磁性能,采用X射线衍射和磁滞分析法分别研究位错密度、最大磁导率、矫顽力和剩磁的演变规律。结果表明:退火前后工业纯铁的近等轴晶组织没有明显变化,晶粒度约为3.70级;随着650℃退火时间延长至5 h,位错密度从初始热轧态1.80×10^(14)m^(-2)逐渐降低至1.16×10^(14)m^(-2),降幅约35%,同时衍射峰在退火初期发生一定程度左移,并在后期明显右移,表明微观存在压应力及后续释放过程。随退火时间延长,最大磁导率整体呈上升趋势,矫顽力和剩磁存在突变点,磁滞回线形状较窄、变化不大,分析认为主要与位错密度、内应力和含碳量相关。退火处理可以改善工业纯铁的磁性能,进一步考虑成分进行一体化调控将提升工业纯铁磁性能并拓展其电磁应用空间。