Double-layer particulate magnetic recording media

Double-layer media employ two layers with different magnetic characteristics, with the objective of optimizing performance and/or reducing the overall cost. The idea has recently been applied to longitudinally oriented thin top layers of Ba-ferrite (BF) or metal particle (MP) coated over thicker Co-iron oxide (CoFe) or non-magnetic (NM) underlayers resulting in significantly improved recording performance for high recording density video, digital audio and data applications.     

Erasure of high-energy magnetic tape recording media

The erasure characteristics of CrO₂, Co−γ-Fe₂O₃, Ba ferrite, metal-evaporated and metal particle tapes were examined. It was found that the Ba ferrite sample was the hardest to erase, and the CrO₂ the easiest. For all the media studied, except Ba ferrite, longitudinal ac fields yield higher degrees of erasure than dc fields. Time domain measurements indicated that particle orientation dispersion plays an important role in the erasure process.     

Writability issues in high-anisotropy perpendicular magnetic recording media

Challenges and recent developments associated with writability issues in high-anisotropy perpendicular recording media are reviewed. The writing field is limited by the high coercivity caused by the high anisotropy. Some new alterna- tives are proposed to solve the writability issues, including texture-tilting-assisted, domain-wall-assisted, energy-assisted magnetic recording technologies, and so on, In addition, we propose new alternatives for the next-generation of magnetic recording media.     

Extracting intergranular exchange coupling in perpendicular magnetic recording media

A micromagnetic numerical technique has been used to demonstrate how intergranular exchange coupling and intrinsic anisotropy field dispersion can be extracted from measuring two types of M-H curves. A realistic grain configuration formed by planar Voronoi cells is used to simulate perpendicular magnetic media. This technique effectively separates the effects of intergranular exchange coupling and anisotropy dispersion by finding their correlation to differentiated M-H curves with different initial magnetization states, even in the presence of thermal fluctuation. The validity of this method is investigated with a series of intergranular exchange couplings and anisotropy dispersions for different media thickness. A relationship between the auto-correlation function of an ac-erased sample and dispersion of the exchange interaction is demonstrated. Utilizing magnetization auto-correlation functions, the magnetic intergranular exchange coupling statistics show a correlation with the auto-correlation function shape in terms of zero-cross and undershoot values.     

Characterization of media cross-track thermal profile in heat-assisted magnetic recording

In the heat-assisted magnetic recording, the thermal profile of the media affects the recording performance seriously. Unfortunately, there is no direct method to measure it dynamically. In this paper, an indirect method is proposed to characterize the cross-track thermal profile with the spin-stand. The experimental results indicate that the local temperature increase has nonlinear relationship with the laser power. As the laser power increases, the thermal profile width increases. The media has a higher temperature increase and a bigger thermal profile at a slower rotation speed. The reasons for these phenomena are explained as well.     

Measurement of angular-dependent hysteresis loops in perpendicular magnetic recording media

The intrinsic angular-dependent hysteresis loops in perpendicular recording media have been measured by iteratively correcting the demagnetization effect in order to maintain the internal total field at a fixed angle. Both the angle and the magnitude of the applied field are adjusted simultaneously to compensate for the demagnetization field change. Significant differences have been observed between the conventional angular-dependent hysteresis loop with a constant applied field angle and the intrinsic angular-dependent hysteresis loop with a fixed total field angle. Without demagnetization corrections, the field range in which irreversible magnetization occurs changes as a function of the field angle, whereas it remains constant if proper demagnetization field corrections are applied.     

Theory of longitudinal digital magnetic recording on thick media

A theory of the digital magnetic recording process has been produced which facilitates the prediction of the recording properties of thick particulate and other media. It allows studies to be made of recorded patterns through the depths of media and the influence of these on overall recording properties. The theory is capable of dealing with particulate, thin-film and multilayer media.     

Periodic structure of acicular magnetic clusters in a magnetic liquid

The behavior of magnetic clusters in a magnetic liquid placed in a circular capillary is considered. When a uniform magnetic field is applied to the system, acicular clusters grow from the sediment, being aligned with the field. The interaction of the clusters as magnetic dipoles with one another and with an external gradient magnetic field is considered theoretically. In a nonuniform symmetric magnetic field with a peak, the cluster distribution is uniform near the peak. Such a distribution is fairly stable when the magnetic field gradient is varied over certain limits. The ordered (periodic) cluster configuration is realized experimentally, and it is shown that its period can be controlled. As the magnetic field gradient exceeds a certain threshold, the clusters are redistributed, forming a multirow hexagonal array.     

Sm–Co films for high-density magnetic recording media

In this experiment, Cr–Cu thin film was used as an underlayer for Sm–Co film. The magnetic properties and crystal structure of Sm–Co films prepared onto this kind of underlayer have been studied. Grain size and surface roughness have been reduced with the introduce of Cr. The Cr addition into the Cu underlayer also improves the c-axis orientation of Sm–Co films. As a result, films with squareness ratio as high as 0.95 and perpendicular coercivity as high as 12.3 kOe have been prepared.     

Prospects for bit patterned media for high-density magnetic recording

Prospects for bit patterned media (BPM) of more than 1 Tb/in² are discussed. Improvement in the pattern drawing for small feature size and high precision is necessary for fabrication process. Deviation in the magnetic properties should be estimated and reduced. The etching damage seems not to be large. Design of the substructure of the magnetic dot is necessary for reducing the deviation. BPM is also a good template for technologies to increase the recording density. Combination of BPM with heat-assisted recording or exchange-coupled layers is advantageous for high-density recording.     

Preparation and recording characteristics of granular-type perpendicular magnetic recording media with thin intermediate layer

Granular-type media with thin Ru intermediate layer were prepared on a highly oriented high-B_s FeCo soft underlayer (SUL). A CoPt–TiO₂ recording layer on a Ru intermediate layer of only 2 nm had high-crystal orientation, high H_c of 6.5 kOe, and a high squareness ratio (SQ) of 0.99. The magnetic property of the SUL was also good. The recording performance was measured for the media with different Ru intermediate thicknesses by using a single-pole-type (SPT) head. The media had large reproduced output even for the Ru intermediate layer thickness of 2 nm.     

The design of polymers for high density magnetic recording media

Polymers are responsible for a large proportion of audio/video/computer tape characteristics. Several years ago, the polymers used as a binder were selected only empirically without fundamental study. From this standpoint, the authors have systematically investigated the different effects of functional groups of various polymer binders on electromagnetic performance. As a result, it was found that the proper design of polymer binders offers significant potential for further improvement in magnetic performance. With the recent introduction of high dispersion and high durability binders, it has become clear that the particulate media like a metal tape dominates in the field of higher density recording media such as an 8 mm and Hi-8 video tape, a professional video tape like a Beta CAM SP, D2, D3, UNIHI and 1.2 Gb/s HD, and a DAT streamer tape.     

热辅助磁盘探针存储的研究

描述了一种热辅助磁盘存储技术，该技术可应用于未来的高密度磁盘存储.记录介质是一种CoNi/Pt多层膜，它可用作垂直模式的磁记录介质.使用扫描隧道显微镜(STM)产生的隧道电流作为热源对磁膜进行局部加热.隧道电流随着加在STM针尖与磁膜之间的脉冲电压幅值的增大而增大.实验结果显示了圆形记录点在磁膜上生成，记录点尺寸与电压值相关，阈值电压为4V左右.当电压高于阈值时，记录点尺寸随着电压的增大而增大,平均尺寸为170nm；当电压低于阈值时，未发现记录点.一个简单的模型解释了以上实验现象. 关键词： 扫描隧道显微镜 热辅助磁盘存储技术 高密度磁盘存储     

Density limits imposed by the microstructure of magnetic recording media

The fundamental limit of magnetic recording density on conventional media is set by the grain size. Once this grain size limit is reached, only a reduction of the grain size allows an increased SNR and thus an increased areal density. It is shown that, whilst maintaining thermal stability, scaling demands that the required anisotropy energy density K is proportional to the areal density, or the square of the areal density if the medium thickness reaches the critical thickness (A is the exchange stiffness of the material). Recording onto materials with such a high anisotropy requires some form of a write-assist. It is furthermore shown that the grain size limit cannot be obtained with intergranular exchange present, and six different requirements are listed that constitute ideal media. An alternative path for increasing areal density of magnetic recording is to use patterned media, where each bit contains only one grain. In this case, written-in errors dominate system performance and the maximum achievable areal density is estimated to be about 6 Tbit/in². Patterned media need to exhibit narrow distributions of their physical and structural properties with standard deviations of the order of 5% or less.     

The role of nucleation field of media in heat-assisted magnetic probe recording

We characterize a method of heat-assisted magnetic probe recording on perpendicular media. Heating source is field emission current from a scanning tunneling microscope (STM) tip. Recording media are three kinds of magnetic films, Co/Pt, CoNi/Pt, and Co/Pd multilayers with different nucleation fields. Pulses with amplitude of 5 V were applied between the STM tip and the recording medium. Experiments show that magnetic marks with an average size of 180 nm were formed on both Co/Pt and CoNi/Pt films whose nucleation fields are greater than their saturation magnetization. No marks were observed on the Co/Pd film whose nucleation field is smaller than its saturation magnetization. A model is built to simulate the dynamic process of domain formation in probe-based magnetic recording system. Simulation results agree with experiments and it explains the effect of the nucleation field of medium in perpendicular recording.     

TiN underlayer and overlayer for TbFeCo perpendicular magnetic recording media

TiN thin film is prepared by DC reactive sputtering in Ar+N₂ atmosphere and its suitability as underlayer and overlayer for TbFeCo perpendicular recording media as well as its effect on the magnetic properties of the latter have been studied. Only 5 nm TiN overlayer and 20 nm under layer can successfully protect the TbFeCo film from oxidation. Initially the coercivity is increased sharply from about 2 to 6 kOe for an increase of underlayer thickness to 60 nm then the increasing rate of coercivity becomes very slow. The saturation magnetization remains almost constant with the underlayer thickness. The remanent squareness ratio remains constant at 1.0 with the underlayer thickness up to 60 nm then decreases.     

The limits to magnetic recording — media considerations

At present longitudinal magnetic recording systems are the basis of all low cost high-density information storage systems. During the recent past the data density stored on rigid disk media which is the higher density format have increased at the rate of 60% per annum compound. However, very recently due to the introduction of new advanced GMR spin-valve heads this rate of advance has increased to 100% per annum in laboratory demonstrations. Hence, it is pertinent at this time to enquire as to where the fundamental physical limitations of longitudinal magnetic recording may lie. In this context there are two principle areas of interest: the first of these is limitations to data rate. These are concerned with the fundamental physics of the maximum rate at which a magnetic moment may reverse from one direction to the other. The theoretical calculation of these limits is complex and not well understood but the limits of our understanding will be reviewed in this paper. Secondly, and of principle concern is the limit to the density at which information can be stored in a magnetic thin film. This latter limitation is based around the signal to noise ratio and also the question of the stability of increasingly small written bits. Signal to noise considerations are extremely complex and derive from factors such as the shape of bits and cross-talk between neighbouring bits or even neighbouring tracks. In this article the fundamental origins of noise will be reviewed in terms of the basic physics that gives rise to variation in transition shapes. Cross-talk and cross-track interference will not be discussed as these are generally addressed through issues associated with the resolution of the servo-mechanism that positions the head above a track and is not associated with the fundamental physics of the medium itself. Thermal stability of a bit of information is of critical importance particularly as media is made ever thinner and will form a major aspect of the discussion in this work. Finally, possible material physics solutions to some of these limitations will be presented in terms of measurable parameters which to some limited degree may be controlled by process conditions.     

SNR improvement by intergranular exchange coupling in CGC perpendicular magnetic recording media

Effect of intergranular exchange coupling in coupled granular and continuous (CGC) perpendicular media was investigated in terms of improvement of signal-to-noise ratio (SNR). The exchange coupling improves SNR and byte error rate (BER); however, it tended to widen the magnetic track width (MWW) of a track. That degradation is of concern for the CGC media. This paper discusses intergranular exchange coupling in CGC media to optimize track density and linear density to achieve high areal density.     

Overwrite recording on different recording media

A contact printing model is introduced to explain the re-recording dip in overwrite recording. The first signal on a recording medium is transferred to the medium surface, where the second signal increases the susceptibility to transfer the S-1 signal magnetically with opposite phase. The output signal of S-1 will be compensated by the transferred signal, and will be zero, which is supposed to be the re-recording dip. The contact printing model is confirmed by experiments.     

Remanence in high-density recording media

The uniaxial anisotropy of independent single domain ferromagnetic grains in high density CoCrPtTa longitudinal recording media was derived from remanence measurements. The distribution of the uniaxial anisotropy axis directions was estimated from a measurement of the Kerr rotation in a perpendicular field. The dispersion of anisotropy fields was estimated from the remanence measurements after application of pulse fields in the film plane. Application of an external field to 45° from the film plane results in sharp magnetization reversal with a minimum writing field.