Laser recording on MnBi films

The results of laser recording experiments in which a magnetic field controls the magnetization distribution along Curie-point switched micron-wide tracks are described. These experiments showed that analog as well as digital information may be recorded in this manner.     

Media for erasable magnetooptic recording

Amorphous rare-earth-transition-metal alloys are considered as materials for magnetooptic information storage. They can be prepared by evaporation or sputtering on glass or polymer substrates. The alloys are ferrimagnets and exhibit a uniaxial magnetic anisotropy. The magnetic and magnetooptic properties can be well tailored by the composition as well as the deposition conditions. The information is stored by memory magnetic domains which can be written by a thermomagnetic switching process. The reading process utilizes the magnetooptic Kerr effect. In both cases the temperature profile of the saturation magnetization, the uniaxial anisotropy, and in particular the coercivity are of primary importance. At present, the most prominent candidates for device applications are GdTb-FeCo and Tb-FeCo alloys. Carrier-to-noise values up to 61 dB (30 kHz) have been achieved using magnetooptic disks     

Ferrimagnetic garnet films for magnetooptic information storage

Reversible magnetooptic memories are believed to compete favorably with magnetic bubble devices and CCD's if economic low-power light sources can be used. For optical information storage at data rates of >10⁶bit/s and blocks of 10³bit, memory materials are required exhibiting an optical recording sensitivity on the order of the photographic plate. The presented contribution outlines the recently proposed concept of a magnetooptic/photoconductive sandwich, called MOPS, and shows that certain ferrimagnetic garnet compositions can especially be adapted to such applications.     

Thermomagnetic writing in homogeneous MnBi films

The specific Faraday rotation of the homogeneous low-temperature phase (LTP) and quenched high-temperature phase (HTP) MnBi films used for the writing experiments was measured to be9.5times10^{5}degrees per centimeter and4.3times10^{5}degrees per centimeter, respectively, at 25°C and a light wavelength of 632.8 nm. The coercive field of the films decreased exponentially with increasing film thickness for both phases. Thermomagnetic writing experiments showed that the written spots (1 to 10 μm in diameter) were not satisfactorily stable for films thicker than 50 nm. If thicker films are to be used for magnetooptic memory applications, they should possess larger wall-motion fields than the films investigated, in order to achieve stable spots. The erasure field of the spots was found to depend on the strength of the applied writing field and on the duration and the power of the heating laser pulse. A writing-erasing hysteresis was recorded by means of the Faraday effect. A thermal saturation field is introduced and measured in dependence on film thickness for LTP films. With the help of this field and wall-pinning effects, thermomagnetic writing in MnBi films is discussed.     

An electron microscopic study on MnBi thin films

The structure and orientation of MnBi thin films prepared by sequential evaporation of bismuth and manganese on glass substrates were studied by transmission electron microscopy and electron diffraction. Results indicate that these films develop a preferred orientation with thec-axis perpendicular to the film plane. This preferred orientation is due to the formation of MnBi from a highly oriented bismuth layer, i.e., a layer with thec-axis perpendicular to the film plane. Trace amounts of elemental bismuth, manganese and MnO are found in these MnBi films. There is evidence of close parallel alignment between the MnBi and the bismuth lattices.     

Reflective thin films for information recording

Films (100–1000 Å) of In, Sn, Ag and several other metals were deposited on stationary and moving substrates of a photoconductive thermoplastic material. The resulting composite was heat deformable and was used in an electrophotographic process for recording relief images. The metal films had an island structure and high electrical resistance. A heat pulse applied to the composite to melt the thermoplastic momentarily resulted in an increased reflectance and decreased transmittance of In and Sn films.     

FePt nanocluster films for high-density magnetic recording

High anisotropy L1(0) ordered FePt thin films are considered to have high potential for use as high areal density recording media, beyond 1 Tera bit/in2. In this paper, we review recent results on the synthesis and magnetic properties of L1(0) FePt nanocomposite films. Several fabrication methods have been developed to produce high-anisotropy FePt films: epitaxial and non-epitaxial growth of (001)-oriented FePt:X (X = Au, Ag, Cu, C, etc.) composite films that might be used for perpendicular media; monodispersed FePt nanocluster-assembled films grown with a gas-aggregation technique and having uniform cluster size and narrow size distribution; self-assembled FePt particles prepared with chemical synthesis by reduction/decomposition techniques, etc. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. FePt and related films show promise for development as heat-assisted magnetic recording media at extremely high areal densities. The self-assembled FePt arrays show potential for approaching the ultimate goal of single-grain-per-bit patterned media.     

High-anisotropy nanocluster films for high-density perpendicular recording

This paper reports results on the synthesis and magnetic properties of L1/sub 0/:X nanocomposite films, where L1/sub 0/=FePt, CoPt, and X=C, Ag, etc. Two fabrication methods are discussed: nonepitaxial growth of oriented perpendicular media, and monodispersed nanoparticle-assembled films grown with a gas-aggregation source. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. The films show promise for development as recording media at extremely high areal densities.     

Sputtered multilayer films for digital magnetic recording

Layered films of cobalt over chromium deposited by dc sputtering onto heated substrates exhibit magnetic properties suitable for digital saturation recording. A cobalt layer of a few tens of nanometers thickness deposited over a chromium layer of several hundred nanometers has coercivity between 1100 and 300 Oe and remanence-thickness product between 0.014 and 0.07 G.cm with squareness between 0.7 and 0.95. Additional alternate layers of chromium and cobalt can increase remanent flux without reduction of coercivity. Magnetic properties can be tailored to specific needs by varying layer thicknesses.     

Thin metallic films for high-density digital recording

Three different methods, electrodeposition, autocatalytic deposition, and vacuum deposition, by which thin metal films may be made are described. They have a combination of magnetic characteristics which should make them well suited to the purpose of high density recording. It is concluded that the factors which are primarily responsible for the superior recording performance of these films when compared with the conventional particulate coatings are their thinness and their high coercivity.     

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.