Physics of perpendicular recording with a patterned soft underlayer

In this paper, it is argued that perpendicular recording in the most popular current form--with the use of a continuous soft underlayer (SUL)--may not be the most optimal way to maximize the achievable areal density. As a possible solution, patterning of SUL is discussed. The purpose of patterning of a SUL is to effectively move the image head closer to the recording media, as compared to the real recording head, and thus increase the net recording field and the field gradient across the thickness of the media. Various patterning configurations and combinations with recording layers are comparatively studied. It is illustrated that with a patterned SUL, the recording and sensitivity fields, responsible for writing and reading information, respectively, could be not only increased by several factors but also localized across the entire thickness of the recording media.     

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.     

FeTaC magnetic soft underlayer for L1(0) FePt based perpendicular recording media

FeTaC magnetic soft underlayer under elevated temperature process conditions for L1(0) FePt based perpendicular recording media has been investigated. After annealing FeTaC for 40 min at 350 degrees C, saturation moment increases to 750 emu/cm3 and, coercivity and remanent moment reduce to 2.3 Oe and 166 emu/cm3 respectively. The microstructure of FeTaC annealed at 350 degrees C for 40 min composes of Fe nanocrystals with random orientations immersed in an amorphous matrix. FeTaC surface roughness due to elevated temperature process is reduced by 100 W RF plasma etching and CrRu with (200) orientation is developed. It is found that changing elemental composition due to C diffusion into the CrRu layer and RF preferential etching over Fe, Ta and C has the influence on the magnetic properties of FeTaC.     

Soft magnetic and high-frequency properties of Ni-Zn ferrite film with FeMn underlayer

Ni_0.45Zn_0.55Fe₂O₄ (40 nm) single-layer and Fe₅₀Mn₅₀ (25 nm)/Ni_0.45Zn_0.55Fe₂O₄ (40 nm) bilayer films were prepared on Si(111) substrates by radio frequency magnetron sputtering at room temperature, and the influence of FeMn underlayer on the microstructure and magnetic property of Ni-Zn ferrite film has been investigated. It was found that the introduction of Fe₅₀Mn₅₀ underlayer resulted in a decrease from 7.1 to 3.1 kA/m in coercivity and increase from 0.22 to 0.60 in residual magnetization ratio of the ferrite film. The complex permeability μ = μ′ − iμ″ values of the films were measured at a frequency of up to 5 GHz. An obvious resonance peak at about 1.65 GHz of the bilayer film appeared in the permeability spectrum. The reason has been researched preliminarily and was ascribed to the change of the film's microstructure with FeMn underlayer.     

Structural effects of Ti underlayer on CoCrPt magnetic films

The effects of long-range and short-range orders of Ti underlayer thickness on the magnetic properties of sputtered Co72 Cr21 Pt7 films were investigated using synchrotron X-ray scattering and X-ray absorption near-edge structure spectroscopy. The results were consistent with that of magnetic measurements and X-ray photoelectron spectroscopy. For thin Ti underlayers (10 nm), the oxidation of Ti and significant mixing of other elements within this underlayer did not promote texture development, further resulting in poor texturing of magnetic films and undesirable magnetic properties. Increased crystallinity and texture of metallic Ti in thicker underlayers enhanced the magnetic peak alignment and its properties.     

Magnetostriction and stress-induced playback loss in magnetic tapes

A direct correspondence between magnetic tape playback level, stress-induced remanence loss, and magnetostrictive properties of corresponding magnetic oxides has been observed. From these results the amount of playback loss was estimated by stressing a short segment of tape, by measuring magnetostriction in compacts of magnetic pigments or by an analysis of the Fe²⁺and Co²⁺content if the state of the cobalt within each particle is known.     

An analysis of the magnetic field of a ring head with a highly permeable underlayer

An idealized mathematical model of the magnetic field due to a ring head with a highly permeable underlayer is solved using Fourier analysis. Accurate Fourier coefficients are derived for a range of gap dimensions. The leading term of the resulting exact series is shown to be equivalent to a previously published approximation, but it is demonstrated that this term alone is not normally sufficient to predict the field accurately.<>     

磷化工艺对铁基软磁复合材料电磁性能的影响

研究了磷化工艺对铁基软磁复合材料电磁性能的影响。XRD、SEM、EDS分析和元素面分布结果表明,合适的磷化工艺能在铁粉表面生成1层很薄的非晶或纳米晶结构磷酸盐,并且包覆完整均匀。磁性能测量结果表明,室温条件下用0.01g/mL磷酸对铁粉进行磷化30min,所得到的磷化铁粉磁芯具有优异的综合电磁性能。随着磷酸浓度的增大,磷化时间的增长和磷化温度的提高,软磁复合材料磁芯的电阻率增大,中高频磁损耗不断降低,同时磁导率也有一定程度的降低。     

Cr底层对DyCo薄膜磁性能与结构影响研究

采用磁控溅射法制备了DyCo/Cr非晶垂直磁化膜.振动样品磁强计(VSM)测试结果显示,有无Cr底层的DyCo薄膜都具有垂直磁各向异性,加入Cr底层能将DyCo薄膜的矫顽力从163kA/m提高到290kA/m.薄膜断面扫描电镜(SEM)照片可以看出,Cr底层能够诱导上层的DyCo薄膜形成柱状结构.这一柱状结构导致了薄膜矫顽力的提高.     

Microstructure evolution and soft magnetic properties of Fe-based nanocrystalline soft magnetic composites coated with lubricant

Here, the influence of zinc stearate on the microstructure and soft magnetic properties of the Finemet nanocrystalline soft magnetic composites (NSMCs) was systematically investigated. The results demonstrate that the core loss (P_cv) decreases and the effective permeability (μ_e) increases of the NSMCs with increasing zinc stearate from 0 wt% to 2.0 wt%, which can be attributed to the reduction of residual stress during compaction. Further increasing zinc stearate up to 3.0 wt%, the P_cv increases sharply, while the μ_e shows a decreasing trend. It can be considered that the addition of excess lubricant decomposes to CO₂ during annealing, which deteriorates the magnetic properties. After annealing at 560 °C, a thin hybrid layer of only about 53.6 nm containing iron phosphate, ZnO, and SiO₂ is formed in the NSMCs with 2.0 wt% zinc stearate, which exhibits excellent soft magnetic properties such as low P_cv of 174 kW/m³ and high μ_e of 66.7 at B_m = 0.1 T for 50 kHz. In addition, loss separation has been carried out and suggests that the addition of lubricant mainly affects hysteresis loss in the total energy loss of NSMCs.     

溅射工艺及底层对SmCo薄膜磁性能的影响

用多靶射频磁控溅射系统在玻璃基片上制备了SmCo磁性薄膜。并采用控制变量法研究了溅射功率、溅射时间以及溅射气压等工艺参数对薄膜磁性能的影响。结果发现，当磁性层溅射功率为60W,溅射气压为0.5Pa，溅射时间为8min；底层溅射功率为125W，溅射气压为0．5Pa，溅射时间为4min时，薄膜的矫顽力高达2．79×10^5。底层对SmCo薄膜的磁性能也有影响，振动样品磁强计测量结果表明：相比Cr、Ti底层，以Cu作为底层所得到的SmCo薄膜磁性能更好，薄膜矫顽力分别比用Cr、Ti作底层时高出56％，40％。     

Ag底层对TbFeCo薄膜磁性能的影响

采用射频磁控溅射法在玻璃基片上制备了TbFeCo/Ag非晶垂直磁化膜，研究了Ag底层厚度对TbFeCo薄膜磁性能的影响。原子力显微镜、振动样品磁强计与磁光盘测试仪测量结果表明：薄的银底层具有较高的表面粗糙度可以显著增大TbFeCo薄膜的矫顽力，改善TbFeCo薄膜的磁光温度特性，该薄膜有望用作高密度垂直记录介质与光磁混合记录介质。     

A generalized formula for induced magnetic flux in a playback head

The usual reciprocity relation in magnetic reproduction is shown to be one form of a more general expression. This generalization incorporates an arbitrary tensor permeability which represents well oriented recording media. One useful alternate form of reciprocity is shown to involve only the irreversible or remanent recorded magnetization.     

L10 ordered FePt based double-layered perpendicular recording media with (002) oriented FeCo films as a soft magnetic underlayer

The introduction of the soft magnetic underlayer (SUL) in perpendicular recording technology is to further increase the recording areal density. However, problems such as growth of the uncontrollable recording layer and additional media noise contributed from the SUL could be resulted. In this work, a synthetic antiferromagnetically (SAF) coupled (002) oriented Fe₆₅Co₃₅ film as an SUL was developed for L1₀ ordered FePt based double-layered recording media. The crystallography of hetero-epitaxially grown double-layered media CrRu/(Ru/FeCo)₂/Pt/FePt/Ru was demonstrated. The L1₀ ordered FePt based double-layered perpendicular recording media with SAF coupled FeCo films as the SUL were developed.     

Effect of Ag underlayer on microstructures and perpendicular magnetic properties of CoPt nanocomposite thin films

CoPt/Ag films were prepared by magnetron sputtering on glass substrates and subsequent annealing. The dependence of degree of ordering and magnetic properties on Ag film thickness and annealing conditions were investigated. It was found that the Ag underlayer played a dominant role in inducing the (001) texture of the CoPt film after annealing. CoPt films with a thickness about 20 nm and Ag underlayers with a thickness about 70 nm are easy to obtain a large degree of ordering and a perpendicular magnetic anisotropy after annealing at 700 degrees C for 30 min. CoPt/Ag films with out-of-plane coercivity (Hc (perpendicular)) in the range of 13.5-14.0 kOe and a out-of-plane squareness (S(perpendicular)) of 0.97 were obtained after annealing at 700 degrees C for 30 min. Ag underlayer is beneficial to enhance the Hc(perpendicular)and S(perpendicular) of CoPt film significantly. The degree of ordering and perpendicular magnetic properties of the CoPt films which deposited on Ag underlayer are larger than those of the single layer CoPt films.     

Sputtering of FeCo-B amorphous films with soft magnetic properties

Microstructures, optimum sputtering conditions, and annealing methods were investigated for the purpose of obtaining zero magnetostriction amorphous films with good magnetic softness. Sputtering conditions which suppress formation of columnar structure in films were studied, and films with high density were obtained. The mechanism of columnar structure suppression is discussed. Annealing in an ellipitically rotating field is effective to reduce in-plane anisotropy and Barkhausen-type noise, and to obtain very weak anisotropy for high initial permeability. Some of the samples thus obtained exhibit excellent softness with high initial permeability.     

The migration behavior of atomic clusters in early nanocrystalline process of soft magnetic Finemet alloy

The Finemet alloys are commonly used as cores in transformers and generators, stress and field sensors in technological application for their excellent soft magnetic characteristics. To clarify the nanocrystallization mechanism of Finemet especially about the atomic migration in early stage is very essential for developing their distinctive characteristics. In this study, we investigate the migration behavior of atoms in order to clarify the mechanism of the early-stage nanocrystallization in amorphous Finemet alloys. The Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous ribbons were prepared by single-roller melt-spinning process in argon atmosphere, and then annealed at 350 degrees C-400 degrees C for 10 minutes in vacuum. The atom force microscope (AFM) and the coincidence Doppler broadening spectra (CDB) were used to characterize the migration behavior of different atoms in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloy during the early-stage nanocrystallization. The X-ray diffraction (XRD) patterns show that all annealed samples are in the amorphous state. But the AFM observation shows clearly that there are many small atomic clusters (nuclei) which distribute in the amorphous matrix of the annealed samples. With increasing annealing temperature, there is a significant increase in the amount of atomic clusters and a dramatic drop in the average size of clusters with very limited Cu contention in the samples, which reflect the structural evolution into more homogeneity. The CDB spectrum indicates that the peaks of positron annihilation spectrum are gradually reduced, which means the number of grain boundary and the defects in samples are gradually increased. It can be concluded that more defects are introduced by the formation of atomic clusters through atomic migration during the early-stage nanocrystallization in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloys.     

纳米晶软磁材料的磁性能

介绍了纳米晶软磁材料所具有的独特结构和优异的磁性能。从纳米晶软磁材料的微观组织结构和宏观磁特性紧密相关的角度,探讨了铁基纳米晶合金的结构与磁性之间的依赖关系。     

Fe3O4缓冲层对CoFe2O4薄膜磁性能的影响

采用射频磁控溅射在基片Si（100）和Fe3O4（20nm）/Si（100）上制备了钴铁氧体（CoFe2O4）薄膜，制备的薄膜在空气气氛中进行300～1000℃的退火处理，采用XRD、VSM分析了薄膜的微结构以及磁性能。结果表明，制备的钴铁氧体薄膜均具有尖晶石结构，Fe3O4缓冲层薄膜促进了钴铁氧体薄膜的结晶，但降低了钴铁氧体薄膜的垂直各向异性和垂直于膜面方向的矫顽力，而钴铁氧体薄膜的磁化强度和矩形度得到了一定的提高。     

Structural and magnetic behaviour of soft magnetic Finemet-type ribbons

Different kinds of magnetic anisotropies have been induced during the nanocrystallization process of Co- and Ni-rich amorphous ferromagnetic (Finemet) ribbons by the application of a constant stress or an axial magnetic field during the annealing process. Magnetization measurements have evidenced the presence od macroscopic anisotropy in the treated samples. The main goal of this work has been, after a careful DSC study, the structural analysis of the treated ribbons using X-ray Diffraction and Atomic Force Microscopy (AFM), detecting substantial differences in the crystallization state and grain size of the samples depending on the thermal treatment that was carried out. Moreover, AFM measurements revealed in all the treated samples a strong nanocrystallisation of the surface without evidences of amorphous matrix, which contrast with XRD measurements that have shown a high content of amorphous phase in the bulk of the ribbons. Magneto-optical Kerr effect measurements have been performed with the aim to elucidate the complex magnetic behaviour that is expected for the surface of the ribbons, measuring surface hysteresis loops that showed much higher coercive field values than that obtained in the bulk material.