Effects of current on nanoscale ring-shaped magnetic tunnel junctions

Abstract

We report the observation and micromagnetic analysis of current-driven magnetization switching in nanoscale ring-shaped magnetic tunnel junctions. When the electric current density exceeds a critical value of the order of $6\times 10^{6}$A/cm$^2$, the magnetization of the two magnetic rings can be switched back and forth between parallel and antiparallel onion states. Theoretical analysis and micromagnetic simulation show that the dominant mechanism for the observed current-driven switching is the spin torque rather than the current-induced circular Oersted field

Multilevel 3 Bit-per-cell Magnetic Random Access Memory Concepts and Their Associated Control Circuit Architectures

“…A TMR ratio of 100% has been used in the calculation of resistance in Figure 4, which is similar to the ratios currently used in commercial MRAM [37]. Such a treatment for the calculation of the resistance of magnetic tunnel junctions has been shown to compare well to experimental data in ring shaped MTJs and MTJs using artificial ferrimagnets [38,39]. Theoretical calculation of the resistance of GMR structures with multiple states was also shown in the work by Zhang and Levy [34].…”

Minimal switching voltage for magnetization reversals in asymmetric nanorings

“…We consider a typical asymmetric nanoring MTJ which consists of a sandwiched three-layer structure: Co 60 Fe 20 B 20 (3 nm)/ AlO x (0.6 nm)/Co 60 Fe 20 B 20 (2.5 nm) [6,7], which is realistic but schematically shown in Fig. 1(a).…”

“…Previous experiments and micromagnetic simulations indicated that in ferromagnetic rings of micrometer size the current induced circular Amp ere field is the dominant mechanism for switching the vortex states [9], while in those with diameters of less than 100 nm the spin-transfer torque effect predominates in reversal of the onion state [6]. Here we have chosen to investigate nanorings with outer diameter of 200 nm, which were experimentally well studied by Wei et al [7].…”

“…But an important breakthrough has been made recently by demonstrating that the chirality of vortices can be switched by applying a homogeneous magnetic field in asymmetric nanorings, which has an eccentric distance S between the centers of the inner and outer radii [5]. Meanwhile it is found, both by experiments and by micromagnetic simulations [6,7], that the onion states can be switched back and forth simply by applying a spin-polarized current (SPC) in magnetic tunnel junctions (MTJs) due to the spin-transfer torque effect [8], which is a more appealing switching mechanism since SPC is more easily localized than magnetic field, thus preferred by high density storage.…”

“…In fact, it is interesting, both physically and technologically, to see which asymmetric ring can be magnetically switched by a minimal SPC, since SPC as low as possible is always preferred in order to avoid any significant heating effect and thermal noise in magnetic memory devices. By far, the lowest critical current density J C for switching reported is about 6 Â 10 6 A/cm 2 in symmetric nanoring MTJs with diameter of $100 nm [6,7].…”