Reading a magnetic storage medium with a probe that detects tunn

Details Reading a magnetic storage medium with a probe that detects tunn Reading a magnetic storage medium with a probe that detects tunn

1996-05-02

1998-08-11

Swann, Tod R.

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Electrical modification or sensing of storage medium

369 13, 250306, G11B 700

Patent

active

057937435

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a method and to an apparatus for retrieving digital data from a magnetic storage medium by applying polarized electromagnetic radiation.


BACKGROUND OF THE INVENTION

In present-day data processing, the storage of information is a key issue. Although the speed of processing the data has increased tremendously over the last decade, there is a demand for the ability to process ever larger volumes of data. The handling of large volumes of data, however, faces two related problems. The first problem is one of size: The storage facility for a large volume of data is big of necessity, and immediately this brings about the second problem, which is one of speed. The bigger the storage, the longer it takes to address the location where th e desired information sits, and the longer become the paths the information has to travel from its storage location to a processing station. Obviously, storage design must strive at shrinking memory space as much as possible, in other words, aim at increasing storage density.
The invention is aimed at improving the resolution of the detection of magnetic domains having different directions of magnetization. Thus, it concerns all magnetic recording technologies, the most important of which will be discussed in more detail.
The predominant technology of magnetic recording devices appears in form of magnetic hard disks, floppy disks, and magnetic tapes. In the basic process of magnetic recording, a magnetic write head and the storage medium (disk or tape) are in relative motion with respect to each other, The write head creates a magnetic field which emanates from a gap within the head and magnetizes a small region of the medium. The relative motion separates in space the write signals being sequential in time. The recorded information can be recovered by a read head, which is usually, but not necessarily, identical with the write head. For example, dual-element heads exist, utilizing inductive elements for writing and magneto-resistive sensors for reading.
Magnetic storage media can be divided into materials allowing either a direction of magnetization longitudinal to the surface or perpendicular to it. Perpendicular recording media are known for a, at least theoretical, great potential of ultrahigh density recording, whereas longitudinal recording media represent the type of material mostly used in current applications. Both types of material are within the scope of the present invention.
State-of-art resolution in magnetic recording is demonstrated, for example, by T. Yogi et al. in the IEEE Transactions on Magnetics, Vol. 26, No. 5Sep. 1990, pp. 2271-2276, using a longitudinal magnetic storage me combination with a dual-element and achieving a storage density of roughly 0.2 Gbit/cm.sup.2. The linear density corresponds to approximately 80 000 per cm. Very high storage densities have also been achieved with magneto-optic techniques. The writing of bits of information applying these techniques is performed by heating tiny spots of the storage medium with a well-focused high-intensity laser beam to temperatures above the Curie (or compensation) temperature T.sub.C of the material used for the storage medium, in the presence of a magnetic field. At the Curie temperature, the material loses its spontaneous or previous remanent magnetization, and its magnetization can assume the direction of an external field, which they retain after the laser beam, i.e. the source of heat, was turned off.
In known magneto-optic storage devices, the information is read by shining a low-intensity laser beam onto the addressed storage location and analyzing the rotation of the polarization of the reflected light induced by the magneto-optic Kerr effect. (Kerr effect is the name for the change of the polarization of an incident light beam upon reflection at a magnetic material proportional to the magnetization.)
U.S. Pat. No. 4,823,220 describes a detector for detecting the p- and s-components of the light reflected by the magneto-optic storage medium, wherein the p- and s-compon

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