Cell writing selection when using precessional switching in a magnetic random access memory

Precessional switching can be used to selectively write a cell in a matrix of soft magnetic elements organized following a magnetic random access memory (MRAM) architecture. We model the required addressing strategy using a fully analytical formalism. We describe the magnetization trajectories for field combinations leading to nonswitching, switching, and switching with bounce occurrence, assuming a cell being a lossless macrospin with uniaxial in-plane anisotropy. We find quite simple and rather accurate (±0.7%) analytical equivalents of the so-called dynamical astroïd. The latter had been so far determined solely by numerical integrations of the Landau–Lifchitz equation and subsequent dichotomy. Additional heuristic arguments are used to derive the characteristic time scales of the reversal process, which unravels the physics of the magnetization reversal rate along the magnetization vector trajectory. Our analytical study is a useful guideline to assess which field magnitudes and timings lead to reliable precessional switching in MRAM, where complicated other phenomena render cumbersome the purely numerical calculations. To illustrate this, we show how the addressing window is quantitatively reduced in the presence of random intercell dipolar coupling. A necessary condition for an addressing strategy to be reliable is that the intercell dipolar coupling along the easy axis be lower than 18% of the anisotropy field.