Aloys Eiling

Co-modified pigments in magnetic recording

This paper surveys the physical properties and storage performance of the class of 650 Oe pigments, which are presently mainly being used for home video, high-quality audio and will in the future be intended for high-density digital storage applications. The temperature dependence of coercivity, the change of coercivity by annealing of a sample in a magnetic field and various aspects of the switching field distribution are shown up in detail. The different data are discussed within a newly developed comprehensive model of Co-modified particles. The model correlates morphological and chemical data with physical properties and storage performance, especially print-through data and erasability effects.

Temperature dependence of magnetic properties and site occupation of various barium ferrites

Barium ferrites in which Fe or Ba was replaced by various metal ion combinations were investigated. The coercivity, saturation, and remanent magnetization were determined, and X-ray spectra were recorded to detect impurities. The Cu-doped compounds considered exhibit a temperature coefficient of coercivity close to zero. Moreover, several barium ferrites with positive and negative temperature coefficients of coercivity could be prepared. Site occupancies in selected compounds were determined by Mossbauer spectroscopy. >

Transverse magnetic field stability of magnetic pigments

A simple screening method is presented, which allows the prediction of the time-dependent properties of a magnetic tape like erasability and print-through by using static magnetic and Mossbauer measurements. This method is applied to tapes coated with Co-modified iron oxide particles which are known sometimes to show problems with erasability and print-through. The reasons will be discussed within the framework of a theoretical explanation.

Theoretical description of FM audio recording in Hi-Fi-VHS

Theoretical simulation of the magnetic recording process, similar to the Preisach model, is used to describe the video recording process with frequency-modulated audio recording (Hi-Fi VHS). The model is capable of giving a good reproduction of the conditions determined in experiments. Varying the magnetostatic properties of the tape made it possible to study the video and audio recording properties as a function of these parameters and to predict possible methods of tape optimization. It was found that increasing the coercivity is the most promising way to improve the audio playback characteristics. >

The importance of magnetostatics in video recording: a theoretical analysis

Magnetic recording involving the storage of analog video signals is investigated by computer simulation of the writing and reading process. In this theoretical analysis, the writing and playback of full video signals and of a high-frequency sine-wave on video tape is modeled for the video home system (VHS) and the super-VHS in particular. The influence and importance of various media and system data are determined for the storage performance of the chrominance and luminance part of the video signal. The calculated relationships between tape data and output performance elucidate the importance of the various tape properties and enable the tape producer to develop and optimize videotapes. >

Theoretical analysis of video recording

Video recording on magnetic media is investigated by means of a computer simulation of the magnetic recording process. The study is based on a newly developed model of magnetic recording, which is used in this case to simulate the recording of full video signals coded in the color-under mode. The calculations are based on three consumer systems, namely, VHS, S-VHS, and 8-mm video. Computed data are used to elucidate video recording in general and to perform quantitative comparisons with corresponding experimental results. For each of the three systems, RF output, chrominance output, luminance output, and amplitude strengths of intermodulations are evaluated as a function of the deep gap writing field strength. The merits and drawbacks of changes in different media data are analyzed theoretically for S-VHS. >

Magnetic and storage properties of co-modified pigments

Co-modified iron-oxide is widely used for high-density magnetic recording. The modification with Co is necessary to yield an increase of coercivity, which causes a higher reproduce voltage at short wavelengths. The positive improvement of the coercivity is until now usually accompanied by a loss of magnetic and aging stability. In this paper we show that a newly developed Co-modified ferrite material overcomes the shortcomings of the previous types of Co-containing pigments. The improvements include an excellent temperature and aging stability as well as a superior general storage performance in comparison to former Co-modified iron-oxides.

Relations between magnetostatics and analog audio storage performance: a theoretical analysis

Analog recording on a magnetic medium requires system linearity, which is achieved in an anhysteretic magnetization process. A large high-frequency AC field (bias field) is superimposed on the actual signal field. The linearity and slope of the anhysteretic remanence curve depends on the amplitude of the bias field. With increasing signal strength, deviations in the linearity occur that produce harmonics in the reproduction signal, so analog recording is only carried out up to the remanence at which the harmonics reach a certain proportion of the total reproduction level, called the maximum output level (MOL). Recently it was demonstrated that consideration of the coercivity distribution in the magnetic medium alone is sufficient to obtain an accurate description of the recording process, so that for the first time the harmonics and recording level curves can be calculated from the system data. The author deals with quantifying the importance of magnetostatics for the MOL at long wavelengths on the basis of this new model. >

Coercivity distribution of Co-modified ferrites

A new theoretical approach is proposed, which quantitatively describes the origin of the coercivity enhancement and the specific shape of the coercivity distribution curves of Co surface treated iron oxide pigments. Within the model the dependence of the coercivity distribution on the morphology, on the magnetic properties of the original precursor and on the surface treatment process is deduced.

Computer simulation of bias recording. II. Saturation output level

For pt.I see ibid., vol.24, p.2235-46, Sept. 1988. Magnetic recording involving the storage of analog audio signals is investigated by computer simulating the write-read process. Using the magnetic and technical data of the recording system, the calculations result in data on output voltages which are in quantitative agreement with corresponding experimental data. As a concrete example for an application of the model the recording of high-frequency audio signals on cassette recorders is analyzed. The influence and the importance of various media and system data on the saturation output level at 10 kHz are determined on the basis of computer simulation. >