Remanence properties of substituted Ba-ferrite particles for highdensity magnetic recording

In this paper, the remanence properties of Co-Sn, Co-Ti and Co-Ti-Sn substituted Ba-ferrite (BaF) oriented particulate samples are compared with those of some oriented acicular particulate samples. A new parameter, the minor remanence distribution (MRD), is proposed to review the remanence properties of magnetic particles and the capabilities for resisting the recording demagnetization of magnetic recording media. It is shown that the MRD values of the oriented BaF particulate samples were smaller compared to oriented Co-γ-Fe₂O₃ samples, even though the squareness ratios (SR) of some of the BaF samples were smaller than those of the Co-γ-Fe₂O₃ samples. It Is the small MRD, SFD_r, IRS and large DH _r of a medium that can result in a large resistance to the effects of recording demagnetization and therefore in superior characteristics for high density magnetic recording. Since Co-Sn substituted BaF platelet-shaped particles exhibit these characteristics and have a very low temperature coefficient of coercivity, these particles can be expected to be a promising candidate for high density magnetic recording     

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.     

Perpendicular stand-still recording in Co-Cr films

Some features of perpendicular recording were investigated by means of stand-still recording experiments. For this purpose several radio frequency (RF)-sputtered Co-Cr layers of two different compositions were used as media while a Permalloy single pole (SP) head was used as a write transducer. A magnetoresistive transducer (MRT) was utilized to read the recorded pattern. Further, an analytical model was developed enabling the magnetization induced by the head field in the recording medium to be calculated. Both calculations and experimental results show a sharpening of the transition, due to the demagnetizing field. For a good approximation it is sufficient to consider only the vertical head field component and vertical magnetization in the recording medium. This is a consequence of the well-developed perpendicular anisotropy and negligible in-plane remanence of the Co-Cr layers. In addition the read-out signal is completely determined by the magnetic surface charges. The remanent magnetization in the recording medium and therefore the read-out amplitude is limited by demagnetization and consequently determined by the coercivity of the Co-Cr layer. The medium noise of a dc-erased medium indicates magnetic structures of much larger dimensions than the size of the individual crystallites. This noise appears to be dependent on the saturation magnetization of the Co-Cr medium. Activation of the single pole head by a homogeneous field results in a nonlinear behavior, caused by head saturation effects. This is supported by simple one-dimensional calculations of the head field.     

化学沉积CoNiP薄膜的磁性及其在传感器中的应用研究

采用化学湿法沉积制备了Co-Ni-P磁性薄膜,研究了工艺条件对其磁性的影响,并对其作为磁旋转编码器磁鼓记录介质的记录特性进行了分析。研究结果表明,薄膜矫顽力和矩形比随施镀时间增加而下降。当施镀时间为3min时,Co-Ni-P薄膜矫顽力可达42506.4A/m,矩形比为0.55。X射线衍射及扫描电镜结果表明,随施镀时间增加,薄膜矫顽力下降,晶粒尺寸变大,并发生明显的择优取向。将化学沉积Co-Ni-P薄膜应用于磁旋转编码器的磁鼓记录介质,记录特性测试结果表明,输出信号良好,脉冲计数完整,波形良好,可完整写入2048对磁极。化学沉积Co-Ni-P磁性薄膜适合于高精度、高分辨率的磁旋转编码器的磁鼓记录材料。     

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.     

Recording characteristics of electroless-plated perpendicularrecording flexible disks with a perpendicular head

Perpendicular magnetic recording using a main-pole-driven perpendicular head was tested using electroless-plated flexible disks. Soft magnetic NiFeP films, also produced by electroless plating, were used as an underlayer of a perpendicular recording medium in this test. Two types of flexible double-layer media, composed of an electrodeless-plated CoNiReP film with two types of NiFeP underlayers with a coercivity of 2 and 5.5 Oe, were fabricated, and their recording characteristics were measured. A recording density value of 75 kFRPI was obtained for the medium with the softer magnetic 2-Oe underlayer, about twice as high a value as that for the medium with the 5.5-Oe underlayer     

Correlation between magnetic and recording properties in thin surfaces

Correlation between the magnetic properties and the recording performance of magnetic recording surfaces is a subject under very active investigation by several researchers. In this paper we report the results of a study conducted in which each magnetic parameter and the thickness of a recording surface was varied independently, and their effect on recording performance was individually determined. The width at half the amplitude of the pulse readback from an isolated magnetization transition on a recording surface varies proportionally to the one-half power of the thickness, and inversely proportionally to the one-half power of the coercivity; it is essentially independent of the remanent magnetization of the recording surface for coercivities greater than 150 Oe, but become increasingly more dependent on the remanent magnetization for coercivities below 150 Oe. The pulse amplitude varies proportionally to the one-half power of the coercivity, the remanence, and the thickness of the recording surface.     

The micromagnetic propertis of high-coercivity metallic thin films and their effects on the limit of packing density in digital recording

The micromagnetic structures of the high-coercivity, isotropic, and high-squareness thin films of sputtered Co-Re have been investigated using transmission electron microscope (TEM) Lorentz imaging and electron deflection methods. From the behavior of the magnetic ripple structure under applied field and the configuration of the local surface fields observed in these experiments, the existence of magnetic clusters in these films was verified. Based on the interpretation of the field dependence of the ripple formation and the hysteretic properties of the film, it is concluded that the formation of the magnetic clusters is a spontaneous process resulting from intercrystalline interactions and local inhomogeneities in the anisotropy. The effects of such cluster formation on longitudinal magnetic recording were investigated. The results show that the reduction of dipole energy at the transition region between two oppositely magnetized regions can be achieved by a stepwise rotation of the magnetization vector of an individual cluster in the form of a vortex. This type of rotation creates a finite transition length which is limited by the size of the magnetic cluster of the film. Consequently, it is concluded that the maximum packing density for saturation recording in these types of films would be less than that predicted by the phenomenological equation, which was derived based solely on considerations of the demagnetization field and the coercivity of the film.     

Perpendicular magnetization structure of Co-Cr films

In a perpendicular recording system, a Co-Cr film as a medium is capable of storing very high density signals. Lorentz microscopy of 1000 kV TEM was used to observe the structure of recorded magnetizations in Co-Cr films having perpendicular anisotropy. A composite medium of a Co-Cr film with a soft magnetic back layer was shown by Lorentz microscopy to have a horseshoe magnetization structure. The stable antiparallel magnetization of transition in the Co-Cr layer determined the head-on magnetization structure of the soft magnetic back layer, which consists of a new straw-rope domain structure. The perpendicular magnetization structure of the Co-Cr film was found to consist of small domains magnetized through the film thickness which correspond to the columnar microstructure of the film. Since the intrinsic hysteresis loop of a Co-Cr film was shown to essentially have an ideal rectangular shape, it can be concluded that the Co-Cr layer of a composite film can be recorded by an ideal magnetizing process with negligible demagnetizing field at the transition.     

基于元胞自动机的薄膜磁滞回线的计算机模拟

利用Stoner-Wohlfarth模型,概率型元胞自动机的模型和算法,在考虑了退磁场和交换作用的情况下对薄膜的磁滞回线进行了模拟,比较了温度以及和易轴取向变化时磁化曲线以及剩磁矩形比和矫顽力的不同及变化趋势.退磁场和交换作用的引入对磁化翻转过程有显著的影响,剩磁矩形比和矫顽力都有不同程度的提高.     

The magnetic transfer process

The transfer of information from a magnetic surface master to a magnetic surface slave when they are brought in to intimate contact in the presence of an external magnetic field is discussed. The only effective component of the transfer field was found to be the component in the plane of transfer and collinear with the recorded magnetization. Steady fields were found to be only slightly inferior in transfer efficiency to alternating fields, and the optimum amplitude for both is equal to the remanence coercivity of the slave medium. The basic mechanism of the magnetic transfer process is shown to be the establishment of a relatively large susceptibility in the slave by the transfer field, thus rendering it a good receptor of the flux emanating from the magnetization gradients in the master. Under certain conditions it was found that digital information could be transferred from a high resolution master onto thick or low coercivity media with a significant improvement in resolution over what could be achieved by direct recording with conventional transducers on the same media.     

Microstructural, compositional and magnetic characterization of electrodeposited and annealed Co-Pt-based thin films

Near-equiatomic Co-Pt thin films with thicknesses of 520 nm were deposited from a single electrolyte onto glass-based Au-coated substrates using the electrodeposition method. The as-deposited Co-Pt-based films were annealed at temperatures from 500 ºC to 700 ºC for 1 h. The phase formation, microstructure and the magnetic properties were analyzed. It was found that with an increase of the annealing temperature the coercivity increases up to 1.18 T due to the transformation to the L1₀ phase. In contrast to the coercivity the saturation magnetization and the remanence were found to decrease upon annealing, due to the decrease of the Co concentration in the Co-Pt film because of the oxidation and the interdiffusion reactions between the Co-Pt thin film and the substrate.     

沉积厚度对L10-FePd颗粒膜结构和磁性能的影响

采用直流磁控溅射法在石英玻璃基片上制备不同厚度的FePd纳米颗粒膜,利用X射线衍射仪、X射线能谱仪、扫描电子显微镜、原子力显微镜和振动样品磁强计表征薄膜的结构和磁性能。结果表明,经过550℃热处理3h后,薄膜的X射线衍射谱中出现(002)超晶格衍射峰,表明薄膜中出现了四方有序结构。随着薄膜厚度的减小其有序化程度增加,在膜厚为47nm时,样品矫顽力达到3.5kOe,剩磁比达到0.94,最大磁能积((BH)_(max))达到17.6 MGOe。FePd薄膜的相转变温度降低,磁性能较好。     

Magnetic properties of sputtered Co-Ir thin films

The magnetic properties of sputtered Co-Ir thin films and the relation between the properties and the film microstructure were studied. Thin films obtained by sputtering a Co-Ir alloy containing 10–20 at.% Ir exhibited high coercivity. The maximum coercivity was obtained for a composition of Co-15at.%Ir. The film remanence decreased with increasing iridium concentration. The film coercivity also increased with an increase in the average grain diameter of the films.     

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.     

Temperature Dependence of Magnetic Properties of SmCo/FeCo Multilayer Films

1. IntroductionIn addition to the magnetic properties of each individual particle, intergrain illteraction play a dominantrole during demagnetization processes[1'2]. These intergrain interactions are sensitively influenced by intergranular phases depending on the respective preparation methodl3'4]. A systematic improvement of permanent magnets is only possible by a deeper understanding of the relations between intergrain interaction, microstructural features, and magnetic properties.In this pa…     

The Influence of Co and Nb Additions on the Magnetic Properties and Thermal Stability of Ultra-high Intrinsic Coercivity Nd-Fe-B Magnets

The effect of Co and Nb additions on the magnetic properties and thermal stability of ultra-high intrinsic coercivity Nd-Fe-B magnets has been investigated. The results show that the remanence (B _r ) and maximum energy product (BH)_max of sintered Nd-Fe-B magnets first increases, and reaches a maximum, then starts to decrease with increasing Co content. The intrinsic coercivity and temperature coefficients of remanence (α) decrease, and the temperature coefficients of coercivity (β) increase with increasing Co content. The minimum reversible magnetic flux loss, temperature coefficients of reversible magnetic flux, total magnetic flux loss and irreversible magnetic flux loss are obtained when the Co content is 7.5 at.%. The temperature coefficients of coercivity (β) and remanence (α) for sintered Nd₉Dy₆Fe_79?x Nb _x B₆ magnets from 300 K to 513 K are 0.36 %/K and 0.127 %/K respectively when the content of Nb is 1.0 at.%. The reasons for the variation on magnetic properties and temperature coefficients were analyzed.     

掺杂Mg对纳米CoFe2O4/SiO2复合薄膜结构和磁性的影响

采用溶胶-凝胶旋涂法制备了纳米Co_1-xMg _xFe₂O₄/SiO₂(x = 0, 0.2, 0.4, 0.6, 0.8) 复合薄膜。利用XRD、SEM、原子力显微镜、振动样品磁强计对薄膜的结构、形貌和磁性进行了分析, 研究了Mg²⁺含量对样品结构和磁性的影响。结果表明, 样品中Co_1-xMg _xFe₂O₄具有尖晶石结构, 晶粒尺寸在38~46 nm之间。随着Mg²⁺含量的增加, Co_1-xMg _xFe₂O₄的晶格常数减小, 样品的饱和磁化强度减小, 矫顽力先增大后减小。样品Co_0.4Mg_0.6Fe₂O₄/SiO₂垂直和平行膜面的矫顽力分别为350.7 kA·m^-1和279.4 kA·m^-1, 剩磁比分别为67.2%和53.9%, Co_1-xMg _xFe₂O₄/SiO₂复合薄膜具有较明显的垂直磁各向异性。     

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。     

Thermo-magnetic recording on a Co/Pt perpendicular film by a sharp metallic probe

We studied a method of heat-assisted magnetic recording (HAMR). The recording medium is a strongly coupled Co/Pt multilayered thin film, suitable for perpendicular recording. Field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 5?V were applied to the film. Experimental results show that an average mark size of 100-120?nm was achieved, with the minimum being 45?nm. Models of domain stability and dynamic domain formation are built to quantitatively explain the experimental results. They agree well with experiments. The models give us future directions for achieving small marks for ultra-high recording density.