Review Modern magnetic materials in data storage

The current status of the technology of magnetic recording as used in disk drives is reviewed. The emphasis is on the magnetic materials used in the application and on some of the technical problems that may limit the increase in areal density. The new technology of magnetic random access memory (MRAM), which has evolved from the magnetic recording application, is also reviewed. A wide range of magnetic materials is essential for the advance of magnetic recording and the MRAM technology. For the magnetic-recording application the requirements are for high-magnetization, soft magnetic materials for write heads, new antiferromagnetic alloys with high blocking temperatures, large coupling to ferromagnetic films and low susceptibility to corrosion for pinning films in giant magnetoresistive sensors, and for the MRAM application, the requirement is for new ferromagnetic alloys with large values of tunneling polarization ratio. A significant limitation to magnetic recording is found to be the inconsistent demands on media thickness: small media thicknesses are required for large values of signal-to-noise ratio, while large values of thickness are required to reduce the impact of the superparamagnetic effect, which results in the potential for data loss over time. Both of these requirements are discussed. Multilayer ferromagnetic films for recording surfaces are shown to allow both large signal-to-noise ratio and adequate resistance to data loss.     

Patterned media write designs

Recording design alternatives are analyzed for 100 1 Gbit/in² vertical and horizontal patterned media, written at 1 Gbit/s with one and two pole heads. Bit write fields, disturb fields, and switching speeds are calculated as part of a system analysis of the theoretical potential of patterned media to address possible physics limits for conventional “featureless” continuous film media (these include thermal decay, nonlinear transition shift and transition noise, and high writer pole M_s requirements near the limit of known materials). The patterned media “bits” are assumed oriented vertically or horizontally by crystalline anisotropy, and smaller than 100 nm to allow single-domain, 1/2 ns switching. M_sH_c V/kT>500, implying thermal stability including media demagnetization and write head remanent fields, are nearly an order of magnitude areal density extensibility beyond 100 Gbit/in² with present-day head/media magnetic requirements     

Transversal recording on radially anisotropic disc

Transversal recording has been described in the sixties, as a promising mode to achieve high density magnetic recording [1]. Because of the improvements in longitudinal and vertical recording introduced by thin film technologies for heads and media, research labs took no further interest in this transversal mode, partly due also to the fact that media and heads were not available at that time. However technological advances of recent years such as the attainment of high B(H) loop squareness for amorphous or crystallized magnetic alloys such as CoxSm1-x[2] and the capability of conventional ferrite heads to record vertical bits on a strongly anisotropic medium [3] allow us to assert that transversal magnetic recording (TMR) can be developed today. This paper describes recent studies for a radially anisotropic disc on a new TMR system. Experimental results on Co-Sm are presented, and the complementary features between the transversal mode and both vertical and longitudinal magnetic recording are discussed.     

Tunneling magnetoresistive heads for magnetic data storage

Spintronics is emerging to be a new form of nanotechnologies, which utilizes not only the charge but also spin degree of freedom of electrons. Spin-dependent tunneling transport is one of the many kinds of physical phenomena involving spintronics, which has already found industrial applications. In this paper, we first provide a brief review on the basic physics and materials for magnetic tunnel junctions, followed more importantly by a detailed coverage on the application of magnetic tunneling devices in magnetic data storage. The use of tunneling magnetoresistive reading heads has helped to maintain a fast growth of areal density, which is one of the key advantages of hard disk drives as compared to solid-state memories. This review is focused on the first commercial tunneling magnetoresistive heads in the industry at an areal density of 80 approximately 100 Gbit/in2 for both laptop and desktop Seagate hard disk drive products using longitudinal media. The first generation tunneling magnetoresistive products utilized a bottom stack of tunnel junctions and an abutted hard bias design. The output signal amplitude of these heads was 3 times larger than that of comparable giant magnetoresistive devices, resulting in a 0.6 decade bit error rate gain over the latter. This has enabled high component and drive yields. Due to the improved thermal dissipation of vertical geometry, the tunneling magnetoresistive head runs cooler with a better lifetime performance, and has demonstrated similar electrical-static-discharge robustness as the giant magnetoresistive devices. It has also demonstrated equivalent or better process and wafer yields compared to the latter. The tunneling magnetoresistive heads are proven to be a mature and capable reader technology. Using the same head design in conjunction with perpendicular recording media, an areal density of 274 Gbit/in2 has been demonstrated, and advanced tunneling magnetoresistive heads can reach 311 Gbit/in2. Today, the tunneling magnetoresistive heads have become a mainstream technology for the hard disk industry and will still be a technology of choice for future hard disk products.     

IEEE Magnetics Society & The IEEE Press call for books

The following topic are dealt with: magnetic actuators; magnetic sensors; magneto-optical recording materials; ferromagnetism; magnetic disk drive technology; magnetic heads; magnetic media; magnetic interfaces; magnetic integration; and magnetic hysteresis.     

1990 International Magnetics Conference. INTERMAG

The following topics are dealt with: recording heads; magnetooptics; hard materials; superconductivity; microwave magnetics; soft films; domains and domain walls; thin-film media; crystalline and amorphous wires; particulate recording media; sensors; soft magnetic devices; biomagnetism; magnetic recording systems; transformers and inductors; multilayers; eddy currents; head-medium interface; solid-state memories; noise in thin-film media; and electromagnetic fields. Abstracts of individual papers can be found under the relevant classification codes in this or other issues     

USE OF THIN SOLID FILMS AT HEAD/MAGNETIC MEDIA INTERFACES

The lubrication of head / disk interlaces in magnetic hard disk drives by physically processed thin films was investigated. Sputtered gold films showed no useful endurance as a protective / lubricating film. Ion-plated carbon films and hydrogenerated carbon films (i-carbon) were effective for preventing tribological damages in magnetic recording media, while amorphous carbon films (a-carbon) were ineffective. The longest durability was found for i-carbons. Raman scattering showed that i-carbons contained much sp³ component, and microindentation test signified that i-carbon films were twice as hard as amorphous carbon films. As a protective film, i-carbon seems very promising, but hard materials should be selected as heads to avoid quick wear of the head. Sufficient performance of i-carbon films may lead to application of thin solid lubricants to hard disk drives.     

Tunable spin-tunnel contacts to silicon using low-work-function ferromagnets

Magnetic tunnel junctions have become ubiquitous components appearing in magnetic random-access memory, read heads of magnetic disk drives and semiconductor-based spin devices. Inserting a tunnel barrier has been key to achieving spin injection from ferromagnetic (FM) metals into GaAs, but spin injection into Si has remained elusive. We show that Schottky barrier formation leads to a huge conductivity mismatch of the FM tunnel contact and Si, which cannot be solved by the well-known method of adjusting the tunnel barrier thickness. We present a radically different approach for spin-tunnelling resistance control using low-work-function ferromagnets, inserted at the FM/tunnel barrier interface. We demonstrate that in this way the resistance-area (RA) product of FM/Al2O3/Si contacts can be tuned over eight orders of magnitude, while simultaneously maintaining a reasonable tunnel spin polarization. This raises prospects for Si-based spintronics and presents a new category of ferromagnetic materials for spin-tunnel contacts in low-RA-product applications.     

Comparison of the magnetic recording performance of medium-scale ring, double-sided pole, metal-in-gap heads on high-coercivity longitudinal media

The magnetic recording performance of medium-scale ring, double-sided pole, and metal-in-gap (MIG) heads were investigated on standard longitudinal high-coercivity floppy, video tape, and isotropic floppy media using a stretched-surface multi-head magnetic recording tester. The isolated pulses for the ring and MIG heads exhibited sharp peaks near tbe edges of the gap for a head-medium separation of less than 0.1 um. Low density maximum output voltage was independent of the type of the write head. The largest output voltage was achieved from the MIG head. The isolated outputs on video media agreed with calculated values for the ring head efficiency set to 52% and the pole head efficiency set to 33% using the Karlqvist head field approximation.     

Multilayer films of CoCrTa for perpendicular recording media

Multilayer structures of alternate magnetic and non-magnetic CoCrTa alloys have been prepared in which the magnetic properties can be widely varied by changing the magnetic layer and interlayer thicknesses, In this way, one example has shown that enhanced perpendicular anisotropy can be achieved as demonstrated by an increase in perpendicular coercivity Hc(perp) and a decrease in longitudinal coercivity Hc(&dlor.). This condition is desirable for application in perpendicular recording media. In addition, a second example has shown that by using much thinner layers (≃15 nm) it is possible to produce a structure in which the magnetization is longitudinal with a very low coereivity of 1.5 Oe. Such soft magnetic films with high Ms and low Hc(&dlor.) can be used as underlayers for perpendicular recording media in order to enhance the efficiency of pole heads.     

Patterning of FePt for magnetic recording

Higher areal density for magnetic recording is needed to provide larger storage capacities on harddisk drives. However, as the recording bit size of traditional magnetic recording materials (such as Co/Cr) approaches 10 nm, the magnetic direction of each recording bit would become unstable at room temperature due to thermal fluctuation. To solve this problem, efforts have been made using two methods: one method is to replace the disk media with new materials possessing higher magnetic anisotropy which would lead to better thermal stability; and the second one is to employ different configurations for the recording layer. FePt with patterned media configuration is a combination of these two methods. In this paper we review some novel and interesting methods of patterning FePt for magnetic recording, including thermal patterning, self-assembly patterning, and lithography patterning.     

A technique for measuring pole tip saturation of low inductance heads

Increasing the coercive force of a magnetic recording medium normally improves high density digital performance. However, in rigid disk systems, the head is not in intimate contact with the disk. In addition, the ferrites employed as head materials have much lower saturation magnetization than the metals normally used in other types of heads. Under these conditions, the head field may be inadequate to fully saturate recording media of higher than normal coercive force. In the development of the latest disk products, increasing the coercive force has not improved performance but has increased overwrite modulation. This situation has not been improved by increasing write current amplitude. Pole tip and core saturation of the record head has been suspected as the cause of these observations. This paper describes a method of characterizing saturation effects in low inductance heads such as those used with rigid disks. Evidence of the deterioration of performance due to pole tip and core saturation is shown from isolated pulse measurements on a rigid disk with NiZn and MnZn ferrite heads.     

Alternate pole materials for MR tape heads

We have investigated the suitability of a number of magnetic films for use as a pole material in MR tape heads. These include nickel iron, cobalt tantalum zirconium, and two cobalt iron alloys. Heads were fabricated using these alloys as pole materials. The heads were tested both for their electrical performance and for their wear characteristics     

Fe3Si基合金的制备及应用研究进展

Ｆｅ３Ｓｉ基合金具有优异的软磁性能,不仅有希望硅钢片（在高频信息领域）,而且还广泛用作音几视频磁头材料和卡片阅读器用磁头材料。本文综述了Ｆｅ３Ｓｉ基合金的制备工艺及应用,并结合我们的研究工作,分析了其研究现状,简要论述了其发展前景。     

Lubrication of tapes with fluorocarbon (FOMBLIN) oils

Fluorocarbon oils, both in their branched (Fomblin Y) and linear (Fomblin Z) forms, were used as topic lubri cants in solutions of trichloro-trifluoro-hethane ( Delifrene LS) for magnetic tapes. This work reports the preliminary results on this inves tigation which is going to be extended to include different aspects of topic lubrication with Fomblin. The surface roughness of the tapes which were used in this preliminary study was too high to allow a straight forward comparison between the bulk lubricated media, the non lubricated ones and those which were topically lubricated with silicon oils in n-heptane solutions; yet, some important conclusions can be drawn. 1. Fomblin is the only lubricant which is not removed from the surface when the media is subjected to a scraping effect (from the heads or the slide used in the friction measuring device); 2. Due to this phenomenon, although the friction and intermodulation of all virgin samples are very symilar, a degradation of the lubricating properties is not found for Fomblin lubricated materials in comparison with sensible losses for any other type of media.     

Preconditioning, write width, and recording properties of Co-Cr-Pt-O perpendicular media with various underlayer designs

The effect of magnetic "preconditioning" on the recording performance of perpendicular media is investigated. Furthermore, the dependence of the magnetic write width (MWW) of shielded-pole heads (SPH) on soft-underlayer (SUL) type and thickness (t/sub SUL/) and the recording performance of perpendicular media with thin SULs are examined. The MWW dependence on SUL structure is influenced by the pole-to-trailing shield spacing. For a wide-gap (/spl sim/80 nm) SPH, thick single-layer, SULs are preferred. For a narrow-gap (/spl sim/50 nm) SPH, MWW is less sensitive to the SUL type. For both narrow and wide-gap SPH and for media with an antiferromagnetically-coupled SUL, MWW is reduced for t/sub SUL/<100 nm. Comparable performance is achieved relative to media with t/sub SUL//spl sim/150 nm.     

From the computer to the laboratory: materials discovery and design using first-principles calculations

The development of new technological materials has historically been a difficult and time-consuming task. The traditional role of computation in materials design has been to better understand existing materials. However, an emerging paradigm for accelerated materials discovery is to design new compounds in silico using first-principles calculations, and then perform experiments on the computationally designed candidates. In this paper, we provide a review of ab initio computational materials design, focusing on instances in which a computational approach has been successfully applied to propose new materials of technological interest in the laboratory. Our examples include applications in renewable energy, electronic, magnetic and multiferroic materials, and catalysis, demonstrating that computationally guided materials design is a broadly applicable technique. We then discuss some of the common features and limitations of successful theoretical predictions across fields, examining the different ways in which first-principles calculations can guide the final experimental result. Finally, we present a future outlook in which we expect that new models of computational search, such as high-throughput studies, will play a greater role in guiding materials advancements.     

Magnetic properties of new (NP) hydrothermal particles

A new type of uniaxial particles for magnetic recording whose precursors are produced via an original hydrothermal process was recently introduced in the market. The characterizing feature of these materials is their extremely uniform size and ellipsoidal shape. Most of their properties can be ascribed to the lack of external (pores, dendrites, sharp edges) as well as internal (because of ellipsoidal shape) - self-demagnetizing sources, which suggests the name of "Non-Polar (NP)" particles. As a result of this morphology, they show unique magnetic properties. The magnetization reversal mechanism is not accounted for by any known mechanism as fanning or curling and the rotational hysteresis gives very sharp Wrvs. H curves with the lowest values for the integral ever measured for particulate media. The behaviour of coercivity versus packing fraction for Cobalt-surface-modified NP particles is described by a new "constricted magnetization" model. The reasons for these unique characteristics and the practical impact that these materials may have in the field of magnetic recording are discussed.     

Magnetoelektronik. Magnetoelectronics

The discovery of strong spin‐dependent transport processes in magnetic materials has triggered the advent of a new research field with a strong application potential: magnetoelectronics. This field is concerned with the development of microelectronic devices based on magnetotransport phenomena. Since these phenomena occur predominantly in ultrathin film systems, their technological exploitation poses significant challenges to thin film preparation and requires careful spin engineering. Magnetoresistive read heads for hard disks have already been successfully introduced on the market, and further applications in information technology, for example, nonvolatile magnetic memory banks (MRAM) are coming within reach. The realization of active magnetoelectronic devices, however e.g., a spin transistor, will need further research work.     

Fabrication of grouped magnetic heads

A new magnetic transducer has been developed for use in the measurement of mechanical displacement. Experiments suggest that the transducer could be used for various purposes: for instance, readout information from magnetic drums or disks of computers, nondestructive readout from thin-film memories, magnetic pattern recognition, and an unconventional flux sensor. The transducer is composed of flux-sensitive magnetic heads which are fabricated from a sheet of ferromagnetic thin film by photoetching process. By using the etching process, a large number of heads are produced simultaneously, and the heads are operated in a group. The characteristics, performances, and an application of grouped magnetic heads are described in this paper.