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Magnetic memory – quo vadis?

Prof. Dr. Nikolai A. Sobolev

University of Aveiro, Portugal

12\5  2018

The use of magnetism for data storage applications has a long history. Information can be stored in some magnetic materials in the form of a magnetization orientation. Nonvolatile magnetic random-access memory (MRAM) was first developed in the early 1950s. A 3D magnetic-core memory module consisted of circumferentially magnetized toroids strung with x-, y-, and z-plane select wires and a fourth inductively driven output-signal wire. At that time, toroid cores were about 2mm in outer diameter. Storage on magnetic tapes and on magnetic hard disk drives (HDDs) and floppy discs was also developed. The increase in the demand for storage capacity has stimulated an increase by eight orders of magnitude in the areal density of information stored in HDDs over the past 50 years; the bit area has decreased by the same factor. This decrease in bit size has required continual improvements in the storage medium, in the write head and in the read head. The discoveries of giant magnetoresistance (GMR) in 1988 and tunnel magnetoresistance (TMR) at room temperature in 1995 have been major breakthroughs from a scientific point of view, but they also helped recording technology keep moving forward. The most recent MRAM solution is the perpendicular magnetic tunnel junction (pMTJ) comprising two out-of-plane magnetized magnetic layers separated by an ultrathin dielectric film, preferentially made of MgO. The device does not have any moving parts, the information is written and read electrically. 

In this lecture, I'll provide a brief overview over the physical principles underlying the various types of magnetic memories, the history of the magnetic memory, as well as describe the most promising technical developments in the field. 

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