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

The authors report on the field variation of the fluctuation field (H/sub f/) in recording media. From theoretical calculations the field variation of H/sub f/ is found to be governed by the distribution of particle volumes and the distribution of anisotropy fields. The decrease in H/sub f/ arises from the volume distribution, while the presence of an anisotropy distribution results in an increase in H/sub f/. Thus, when these two effects are present in the sample, the field variation of H/sub f/ exhibits a minimum. >

Fluctuation fields of recording media particles, the role of anisotropy dispersion

Trends in magnetic recording media

The process of thermally assisted switching in small metallic particles is studied by measuring the field dependent fluctuation fields. A correlation is found between the size of crystallographic sub-units rather than the total volume of the particles and the fluctuation fields. Therefore, very small particles can be more stable magnetically than large particles, if they contain only few large crystal grains. The grain volumes are determined by X-ray line broadening measurements on random and on oriented samples. The effect of thermal activation on the switching process is confirmed by measuring the recording currents needed to optimize high frequency output in tape samples prepared with the same particles. >

Thermal effects in small metallic particles

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. >

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

Samples of chromium dioxide particles with a range of remanent coercivities H/sub r/, but with identical particle size distributions were prepared in order to study the effect of changes in the magnetocrystalline anisotropy on the time-dependent magnetization. Comparisons have been made with three cobalt modified gamma-Fe/sub 2/O/sub 3/ samples. The field-dependent fluctuation field H/sub f/, derived from measurements of magnetic viscosity as a function of applied field H, has been used to characterize the time-dependent magnetic switching of the particles. Plots of H/sub f//H/sub r/ against H/H/sub r/ are unaffected by anisotropy variations in either pigment type. The interpretation is that the details of the magnetics and the reversal mode are not primarily responsible for the more pronounced time-dependent magnetization effects observed in CrO/sub 2/ and that the more likely explanation is the high state of magnetic excitation associated with the low Curie temperature. >

H. Jachow

Papers

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

Viscous magnetization of chromium-dioxide particles: effect of increased magnetocrystalline anisotropy