A thermomagnetic recording system achieves high areal bit density by combining the high linear bit density of magnetic recording and the high track density typical of magneto-optic recording. The system employs a medium which comprises a ferrimagnetic recording material having a compensation temperature approximately equal to ambient operating temperature, yet small coercivity and high saturation magnetization at elevated temperatures. A source of heat (preferably a laser) controls the magnetic properties of the material. Data is recorded and played back with high performance magnetic recording heads, producing direct overwrite capability, at temperatures less than the Curie point of the material.

Thermomagnetic recording system employing a medium having high storage density and direct-overwrite capability as a result of along-track isocoercivity

Magneto-optic media and system optimization including a set of optimized magneto-optic media for use in a magneto-optic recording and readout system employing an incident readout light beam of a given fixed power, P o . The beam is delivered in a linearly polarized state to the magneto-optic media and the magneto-optic radiation received from the media is detectable by the system. Each member of the set of media comprises a reflective layer having a predetermined thickness, a first transparent layer overlying the reflecting layer and having a predetermined thickness and refractive index and a second light transmissive layer having a predetermined thickness and exhibiting absorptivity at the wavelength of said incident readout light beam and having magneto-optic conversivity and perpendicular anisotropy. Members of the set of optimized magneto-optic media may further included a third transparent layer overlaying the second transmissive layer and having a predetermined thickness and refractive index. The combination of these layers exhibit antireflectivity and the incident light absorbed in the media is captured in the second light transmissive layer and the predetermined layer thicknesses and refractive index are chosen to maximize signal to noise ratio (SNR) according to the relationship ##EQU1## where r x represents the reflected component of the linearly polarized incident beam r y represents the reflected magneto-optically induced component in an orthogonal direction, a i is the i th element of the set }a i }0 that represents variable parameters of the chosen readout system, N is the number of elements in the set {a i } and f is a function which is determined by the chosen readout system.

Magneto-optic media and system optimization

A device for the thermomagnetic recording and magneto-optical reading of data by means of the Kerr effect, in which the magnetisable recording medium consists of a monocrystalline or polycrystalline material having a garnet structure in which bismuth ions are present in dodecahedral sites and trivalent iron ions are present in tetrahedral sites. An example of a material having such a composition is Biy3 Z3 y3 Fe33 O122 , wherein Z is a rare earth ion.

Thermomagnetic recording and magneto-optic reading of a medium having bismuth ions in a garnet structure

A heat magnetic recording and reproducing apparatus is disclosed. The apparatus comprises a record medium running in a predetermined direction, a means for generating a laser light beam for locally heating the medium, a magnetic field generating device for generating a magnetic field at the heated portion, an information recording means provided in opposition to the magnetic field generating device and having an auxiliary magnetic pole piece for focusing a magnetic flux from the magnetic field generating device into at least the heated portion, a means provided at a front stage of the information recording means to the running of the medium for generating a laser light beam for locally heating the medium, a magnetic field generating device for generating a magnetic field at the heated portion, and an information erasing means having an auxiliary magnetic pole piece for focusing a magnetic flux from the magnetic field generating device into the heated portion.

Thermomagnetic recording and reproducing apparatus

A method and apparatus for optically writing and reading information as a pattern of magnetic domains in the information recording layer of a record carrier. An optical scanning beam is focused to a diffraction-limited radiation spot for scanning the recording layer, and the region under the spot is subjected to a magnetic field generated by a magnetizing coil energized with a square-wave energizing current having a duty cycle which is modulated in accordance with the information signal. The frequency and amplitude of the energizing current are independent of the information signal, and the frequency thereof exceeds the optical cut-off frequency determined by the size of the radiation spot. Several different values of the information signal can therefore be recorded within a distance equal to the width of the radiation spot in the scanning direction at each position thereof, so that the recorded information density exceeds that corresponding the width of the scanning spot. Read-out is based on the "grey" level produced by the recorded information areas under the scanning spot at each position thereof, so that the same size scanning spot can be used for both writing and reading the record carrier.

Method of and apparatus for writing and reading a magneto-optical record carrier with an information density greater than that corresponding to the size of the scanning spot

A magnetic recording and magneto-optic playback system is disclosed wherein thermomagnetic recording is employed. A transparent isotropic film is heated along a continuous path by a focused laser beam. As each successive area of the path is heated locally to the vicinity of its Curie point in the presence of an applied magnetic field, a magneto-optic density is established proportional to the magnetic field and fixed in place as the area cools once the laser beam moves on to an adjacent area. The magnetic field is varied by an input signal so that the magnetooptic density established in a given area of the film is proportional to the amplitude of the input signal being applied. To play back the recorded data, the intensity of the laser beam is reduced to avoid reaching the vicinity of the Curie point of the film as it is scanned by the laser beam in the same manner as for recording. A Faraday effect analyzer and photo detector are employed as a transducer for producing an output signal.

https://ntrs.nasa.gov/api/citations/19790008075/downloads/19790008075.pdf

Thermomagnetic recording and magneto-optic playback system

Manganese bismuth films having improved characteristics for recording information in analogue form, can be produced by a vacuum deposition of Bi and Mn with an atomic ratio of Mn to Bi between 2 and 3.5 or 1.4 and 1.6, followed by a specialized heat treatment which includes very brief exposure to a temperature between about 275 deg and 300 C. Similar MnBi films can be produced more reliably and reproducibly if the initial Bi layer is annealed prior to deposition of the Mn layer. Such an annealing step renders most other factors of the processing relatively non-critical. Deposition of both initial layers is preferably carried out in a vacuum approaching 10 to the -8th power Torr.

/pdf/manganese-bismuth-films-with-narrow-transfer-characteristics-3gaxickpqm.pdf

George W. Lewicki

Papers

Thermomagnetic recording and magneto-optic playback system

Manganese bismuth films with narrow transfer characteristics for curie-point switching