Relevant aspects concerning the ultimate achievable recording densities for particulate as well as for thin-film media are discussed This review covers the entire range starting from micromagnetics of individual single domain particles, moving on to their magnetic behavior in a particle assembly under particular consideration of the structure being actually obtained in the process of manufacturing recording media, and finally embarking on an outline of recording physics These considerations are not only carried out for longitudinally and perpendicularly oriented recording media but also for media having an arbitrary orientation of the easy axis of magnetization All aspects are discussed and illustrated for the first commercially available thin-film medium on a flexible substrate, which is the metal evaporated tape, ie, the obliquely deposited Co-Ni-O layer for the Hi8 video system >

Media requirements and recording physics for high density magnetic recording

Experimental Metal Particle tapes are demonstrated to generate higher output and narrower pulse widths than commercial Hi8 Metal Evaporated tape. Based on simple signal to noise considerations, we discuss the recording limits of MP, ME and barium ferrite for high density digital recording. Although we find the ME tape to be capable of sustaining the highest areal densities, the difference between ME tape and the particulate tapes is rather small so that we believe no technology switch to ME tape is necessary.

Advances in magnetic tapes for high density information storage

Magnetic recording is a very useful and versatile technology, and one that is continuously evolving to serve the increasing demand for information storage and to meet the challenge of competitors such as optical recording. The basic principles of magnetic recording are described in detail elsewhere and briefly below.The elements of a magnetic recording system are a magnetizable surface layer carried on a flexible tape or on a rotating disk, and a transducer that can both write information to and read information from this surface. The tape or disk, often called a recording medium, and the transducer, called a head, move with respect to each other. The information to be stored is originally contained in an electrical signal, either by direct analog representation or via frequency, phase, amplitude, or pulse-code modulation. In response to this signal, the head in the writing mode generates an intense, localized magnetic field that is capable of changing the direction and degree of the magnetization in the surface material. Each time the input signal changes sign, the writing field changes direction and a transition between regions of opposite magnetization is created. As the head moves along the surface, a series of these transitions is created along a track. The resulting magnetization pattern of the tape or disk becomes itself the source of a spatially varying magnetic field.

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Particulate Recording Media

Trends in magnetic recording media

CrO2 doped with 1--2 wt% Fe3+ on Cr4+ positions is one of the most important materials for magnetic recording in audio, data and video tapes 57Fe Mossbauer spectroscopy was applied to determine the level of iron doping in newly developed high coercivity CrO2 particles It was found that, compared with the conventional preparation process, the new particles contain increased amounts of Fe3+ ions in the CrO2 crystal lattice giving rise to higher magnetocrystalline anisotropy This is reflected in coercivities of up to over 900 Oe All samples contain as a secondary iron-containing phase α-(Cr1-xFex)2O3, the amount of which is higher in samples of the conventional preparation process than in those of the new BASF process Details about the mechanism of the development of doped CrO2 particles in both types of processes were obtained by means of Mossbauer, XRD and wet chemical investigations making possible an optimization of the new BASF process

Magnetic pigments for recording media

Chromium dioxide was introduced in the later 1960s as the first magnetic material capable of high density recording. Since that time a continuous improvement of material properties has been made possible. The most recent improvement concerns particles with coercivities well above 70 kA/m which can be prepared by a modified hydrothermal process without using expensive Ir doping. Although CrO/sub 2/ has a somewhat higher specific magnetization, the static magnetic properties of CrO/sub 2/ and cobalt-modified iron oxides are comparable. There are, however, some significant differences in recording performance. CrO/sub 2/ pigments show better print-through to noise ratios than Co-modified iron oxides of the same mean magnetic volume. There are no problems with erasability, which becomes increasingly difficult to control for high-coercivity cobalt-modified iron oxides. Finally, CrO/sub 2/ is the only pigment material which allows thermomagnetic duplication. >

Chromium dioxide particles for magnetic recording

With recorded wavelengths well under 1 micron the geometric dimensions of the particles start to have significant influence on the output of particulate media. The recorded wavelengths of well under 1 micron being used in video storage approach the length dimensions of standard recording pigments. As a single domain particle cannot support a magnetic transition along its length, the finite length of the particle leads to a reduction in the maximum output signal analogous to the gap loss function and known as length loss. At the same time also the magnetic homogeneity as expressed by (1-S*) becomes increasingly important. The authors experimentally verify the theoretical predictions regarding the influence of the particle parameters by measuring different sets of experimental tapes prepared with appropriate pigment samples. >

H. Auweter

Papers

Chromium dioxide particles for magnetic recording

Experimental study of the influence of particle size and switching field distribution on video tape output

Chromium Dioxide Particles for Magnetic Recording

Cobalt-modified iron oxides with improved aging stability