Multilevel Thermally Assisted Magnetoresistive Random-Access Memory Based on Exchange-Biased Vortex Configurations

Abstract

A new concept of multilevel thermally assisted MRAM is proposed and investigated by micromagnetic simulations. The storage cells are magnetic tunnel junctions in which the storage layer is exchange biased and in vortex configuration. The reference layer is an unpinned soft magnetic layer. The stored information is encoded via the position of the vortex core in the storage layer. This position can be varied along two degrees of freedom: radius and inplane angle. The information is read out from the amplitude and phase of the tunnel magnetoresistance signal obtained by applying a rotating field on the cell without heating the cell. Various configurations are compared in which the soft reference layer consists of either a simple ferromagnetic layer or a synthetic antiferromagnetic sandwich (SAF). Among those, the most practical is one with SAF reference layer in which the magnetostatic interaction between SAF and storage layer was minimized. This type of cells should allow to store at least 40 different states per cell representing more than 5 bits per cell.

Significant Surface Spin Effects and Exchange Bias in Iron Oxide-Based Hollow Magnetic Nanoparticles

“…Exchange bias is a magnetic phenomenon in which magnetic phases of different character are coupled via exchange interaction and their magnetic behavior departs from a simple response, giving rise to a shift from the zero-field position of the hysteresis loop at low temperatures. Although interest in EB is growing, owing to its technological applications in the electronic field (spintronic devices [1], spin valves [2], magnetoresistive random-access memory (MRAM) circuits [3]), or new recording media [4] based on materials where the superparamagnetic limit could be defeated with the help of EB-tailored properties, the detailed understanding of EB is still poorly understood.…”

On the first evidence of exchange-bias feature in magnetically contrasted consolidates made from CoFe2O4-CoO core-shell nanoparticles

“…For this reason, it is mainly focused on thin films 2–6 and nanoparticles 7–10 where the interface between the F and AF phases is easier to control and to characterize. Therefore, it is particularly active in the technological fields involving multilayers or embedded nanoparticles (NPs) in thin films, such as those of magnetic recording heads 11,12 , magnetoresistive random access memories (MRRAM) 13–16 , magnetic sensors 17–19 and high storage capacity magnetic recording media 20 . There are also real potential applications for free NPs when they are in the shape of therapeutic fluids of magnetic hyperthermia or self-pumping magnetic cooling fluids or as supported granular data storage media media among others of course 21–24 .…”

Creation, transport and detection of imprinted magnetic solitons stabilized by spin-polarized current

“…Moreover, experimental observations performed at room temperature, in materials with both perpendicular magnetic anisotropy (PMA) and DMI [11][12][13], together with the topological protection and fast transport [14,15], have pointed out skyrmions as the most prominent magnetic structures to be exploited for building magnetic storage devices, such as the racetrack memories [16]. The magnetic domain wall-based racetrack memory is an established technique [17][18][19][20]. The merit of the skyrmion compared with the domain wall is that the skyrmion is not easy to be pinned by defects or impurities [21].…”