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Keywords:

  • magnetic memory;
  • spin-transfer torque;
  • tunnel junctions;
  • spin-reorientation transitions;
  • strain

Abstract

The data writing and thermal stability of information storage are studied theoretically for a magnetic random access memory (MRAM) composed of a magnetic tunnel junction or multilayer exhibiting giant magnetoresistance. The theoretical analysis focuses on the magnetization switching in the “free” layer of a MRAM cell, which is induced by a spin-polarized current imposing a spin-transfer torque (STT) on the magnetization. It is shown that the writing current in such an STT-MRAM reduces dramatically near a spin reorientation transition (SRT) driven by lattice strains and/or surface magnetic anisotropy and even tends to zero under certain conditions. In particular, at the size-driven SRT in the perpendicular-anisotropy CoFeB-MgO tunnel junctions, the critical current densities for magnetization reorientations between the parallel and antiparallel states are expected to fall to low values of about 1.3 × 105 and −3.3 × 104 A cm−2. Remarkably, STT-MRAMs may combine low writing current with very high thermal stability of information storage (retention over 10 years) even at a high density ≈500 Gbit inch−2.